The Incident Object Description Exchange Format v2
draft-ietf-mile-rfc5070-bis-16

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MILE Working Group                                            R. Danyliw
Internet-Draft                                                      CERT
Obsoletes: 5070 (if approved)                           February 1, 2016
Intended status: Standards Track
Expires: August 4, 2016

           The Incident Object Description Exchange Format v2
                     draft-ietf-mile-rfc5070-bis-16

Abstract

   The Incident Object Description Exchange Format (IODEF) defines a
   data representation for sharing information commonly exchanged by
   Computer Security Incident Response Teams (CSIRTs) about computer
   security incidents.  This document describes the information model
   for the IODEF and provides an associated data model specified with
   XML Schema.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on August 4, 2016.

Copyright Notice

   Copyright (c) 2016 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   include Simplified BSD License text as described in Section 4.e of

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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

   This document may contain material from IETF Documents or IETF
   Contributions published or made publicly available before November
   10, 2008.  The person(s) controlling the copyright in some of this
   material may not have granted the IETF Trust the right to allow
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   Without obtaining an adequate license from the person(s) controlling
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   than English.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   4
     1.1.  Changes from 5070 . . . . . . . . . . . . . . . . . . . .   6
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   7
     1.3.  Notations . . . . . . . . . . . . . . . . . . . . . . . .   7
     1.4.  About the IODEF Data Model  . . . . . . . . . . . . . . .   8
     1.5.  About the IODEF Implementation  . . . . . . . . . . . . .   8
   2.  IODEF Data Types  . . . . . . . . . . . . . . . . . . . . . .   9
     2.1.  Integers  . . . . . . . . . . . . . . . . . . . . . . . .   9
     2.2.  Real Numbers  . . . . . . . . . . . . . . . . . . . . . .   9
     2.3.  Characters and Strings  . . . . . . . . . . . . . . . . .   9
     2.4.  Multilingual Strings  . . . . . . . . . . . . . . . . . .   9
     2.5.  Bytes . . . . . . . . . . . . . . . . . . . . . . . . . .  10
     2.6.  Hexadecimal Bytes . . . . . . . . . . . . . . . . . . . .  11
     2.7.  Enumerated Types  . . . . . . . . . . . . . . . . . . . .  11
     2.8.  Date-Time String  . . . . . . . . . . . . . . . . . . . .  11
     2.9.  Timezone String . . . . . . . . . . . . . . . . . . . . .  11
     2.10. Port Lists  . . . . . . . . . . . . . . . . . . . . . . .  11
     2.11. Postal Address  . . . . . . . . . . . . . . . . . . . . .  12
     2.12. Telephone and Fax Numbers . . . . . . . . . . . . . . . .  12
     2.13. Email String  . . . . . . . . . . . . . . . . . . . . . .  12
     2.14. Uniform Resource Locator strings  . . . . . . . . . . . .  12
     2.15. Identifiers and Identifier References . . . . . . . . . .  12
     2.16. Software  . . . . . . . . . . . . . . . . . . . . . . . .  13
       2.16.1.  SoftwareReference Class  . . . . . . . . . . . . . .  13
     2.17. Extension . . . . . . . . . . . . . . . . . . . . . . . .  15
   3.  The IODEF Data Model  . . . . . . . . . . . . . . . . . . . .  18
     3.1.  IODEF-Document Class  . . . . . . . . . . . . . . . . . .  18
     3.2.  Incident Class  . . . . . . . . . . . . . . . . . . . . .  19
     3.3.  Common Attributes . . . . . . . . . . . . . . . . . . . .  23
       3.3.1.  restriction Attribute . . . . . . . . . . . . . . . .  23
       3.3.2.  observable-id Attribute . . . . . . . . . . . . . . .  24

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     3.4.  IncidentID Class  . . . . . . . . . . . . . . . . . . . .  25
     3.5.  AlternativeID Class . . . . . . . . . . . . . . . . . . .  26
     3.6.  RelatedActivity Class . . . . . . . . . . . . . . . . . .  26
     3.7.  ThreatActor Class . . . . . . . . . . . . . . . . . . . .  28
     3.8.  Campaign Class  . . . . . . . . . . . . . . . . . . . . .  29
     3.9.  Contact Class . . . . . . . . . . . . . . . . . . . . . .  29
       3.9.1.  RegistryHandle Class  . . . . . . . . . . . . . . . .  33
       3.9.2.  PostalAddress Class . . . . . . . . . . . . . . . . .  34
       3.9.3.  Email Class . . . . . . . . . . . . . . . . . . . . .  35
       3.9.4.  Telephone Class . . . . . . . . . . . . . . . . . . .  36
     3.10. Discovery Class . . . . . . . . . . . . . . . . . . . . .  37
       3.10.1.  DetectionPattern Class . . . . . . . . . . . . . . .  39
     3.11. Method Class  . . . . . . . . . . . . . . . . . . . . . .  40
       3.11.1.  Reference Class  . . . . . . . . . . . . . . . . . .  41
     3.12. Assessment Class  . . . . . . . . . . . . . . . . . . . .  42
       3.12.1.  SystemImpact Class . . . . . . . . . . . . . . . . .  44
       3.12.2.  BusinessImpact Class . . . . . . . . . . . . . . . .  46
       3.12.3.  TimeImpact Class . . . . . . . . . . . . . . . . . .  48
       3.12.4.  MonetaryImpact Class . . . . . . . . . . . . . . . .  50
       3.12.5.  Confidence Class . . . . . . . . . . . . . . . . . .  51
     3.13. History Class . . . . . . . . . . . . . . . . . . . . . .  52
       3.13.1.  HistoryItem Class  . . . . . . . . . . . . . . . . .  53
     3.14. EventData Class . . . . . . . . . . . . . . . . . . . . .  55
       3.14.1.  Relating the Incident and EventData Classes  . . . .  57
       3.14.2.  Cardinality of EventData . . . . . . . . . . . . . .  57
     3.15. Expectation Class . . . . . . . . . . . . . . . . . . . .  58
     3.16. Flow Class  . . . . . . . . . . . . . . . . . . . . . . .  61
     3.17. System Class  . . . . . . . . . . . . . . . . . . . . . .  62
     3.18. Node Class  . . . . . . . . . . . . . . . . . . . . . . .  65
       3.18.1.  Address Class  . . . . . . . . . . . . . . . . . . .  66
       3.18.2.  NodeRole Class . . . . . . . . . . . . . . . . . . .  68
       3.18.3.  Counter Class  . . . . . . . . . . . . . . . . . . .  71
     3.19. DomainData Class  . . . . . . . . . . . . . . . . . . . .  73
       3.19.1.  Nameservers Class  . . . . . . . . . . . . . . . . .  75
       3.19.2.  DomainContacts Class . . . . . . . . . . . . . . . .  76
     3.20. Service Class . . . . . . . . . . . . . . . . . . . . . .  77
       3.20.1.  ServiceName Class  . . . . . . . . . . . . . . . . .  79
       3.20.2.  ApplicationHeader Class  . . . . . . . . . . . . . .  79
     3.21. EmailData Class . . . . . . . . . . . . . . . . . . . . .  80
     3.22. Record Class  . . . . . . . . . . . . . . . . . . . . . .  81
       3.22.1.  RecordData Class . . . . . . . . . . . . . . . . . .  82
       3.22.2.  RecordPattern Class  . . . . . . . . . . . . . . . .  83
     3.23. WindowsRegistryKeysModified Class . . . . . . . . . . . .  85
       3.23.1.  Key Class  . . . . . . . . . . . . . . . . . . . . .  85
     3.24. CertificateData Class . . . . . . . . . . . . . . . . . .  86
       3.24.1.  Certificate Class  . . . . . . . . . . . . . . . . .  87
     3.25. FileData Class  . . . . . . . . . . . . . . . . . . . . .  87
       3.25.1.  File Class . . . . . . . . . . . . . . . . . . . . .  88

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     3.26. HashData Class  . . . . . . . . . . . . . . . . . . . . .  89
       3.26.1.  Hash Class . . . . . . . . . . . . . . . . . . . . .  91
       3.26.2.  FuzzyHash Class  . . . . . . . . . . . . . . . . . .  92
     3.27. SignatureData Class . . . . . . . . . . . . . . . . . . .  93
     3.28. IndicatorData Class . . . . . . . . . . . . . . . . . . .  93
     3.29. Indicator Class . . . . . . . . . . . . . . . . . . . . .  93
       3.29.1.  IndicatorID Class  . . . . . . . . . . . . . . . . .  96
       3.29.2.  AlternativeIndicatorID Class . . . . . . . . . . . .  96
       3.29.3.  Observable Class . . . . . . . . . . . . . . . . . .  97
       3.29.4.  IndicatorExpression Class  . . . . . . . . . . . . . 103
       3.29.5.  Expressions with IndicatorExpression . . . . . . . . 104
       3.29.6.  ObservableReference Class  . . . . . . . . . . . . . 106
       3.29.7.  IndicatorReference Class . . . . . . . . . . . . . . 106
       3.29.8.  AttackPhase Class  . . . . . . . . . . . . . . . . . 107
   4.  Processing Considerations . . . . . . . . . . . . . . . . . . 108
     4.1.  Encoding  . . . . . . . . . . . . . . . . . . . . . . . . 108
     4.2.  IODEF Namespace . . . . . . . . . . . . . . . . . . . . . 108
     4.3.  Validation  . . . . . . . . . . . . . . . . . . . . . . . 109
     4.4.  Incompatibilities with v1 . . . . . . . . . . . . . . . . 109
   5.  Extending the IODEF . . . . . . . . . . . . . . . . . . . . . 110
     5.1.  Extending the Enumerated Values of Attributes . . . . . . 110
       5.1.1.  Private Extension of Enumerated Values  . . . . . . . 110
       5.1.2.  Public Extension of Enumerated Values . . . . . . . . 111
     5.2.  Extending Classes . . . . . . . . . . . . . . . . . . . . 111
     5.3.  Deconflicting Private Extensions  . . . . . . . . . . . . 113
   6.  Internationalization Issues . . . . . . . . . . . . . . . . . 114
   7.  Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . 115
     7.1.  Minimal Example . . . . . . . . . . . . . . . . . . . . . 115
     7.2.  Indicators from a Campaign  . . . . . . . . . . . . . . . 116
     7.3.  Incident Report . . . . . . . . . . . . . . . . . . . . . 117
   8.  The IODEF Schema  . . . . . . . . . . . . . . . . . . . . . . 117
   9.  Security Considerations . . . . . . . . . . . . . . . . . . . 156
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 157
     10.1.  Namespace and Schema . . . . . . . . . . . . . . . . . . 157
     10.2.  Enumerated Value Registries  . . . . . . . . . . . . . . 157
   11. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 160
   12. References  . . . . . . . . . . . . . . . . . . . . . . . . . 160
     12.1.  Normative References . . . . . . . . . . . . . . . . . . 160
     12.2.  Informative References . . . . . . . . . . . . . . . . . 162
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . 163

1.  Introduction

   Organizations require help from other parties to mitigate malicious
   activity targeting their network and to gain insight into potential
   threats.  This coordination might entail working with an ISP to
   filter attack traffic, contacting a remote site to take down a bot-

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   network, or sharing watch-lists of known malicious IP addresses in a
   consortium.

   The Incident Object Description Exchange Format (IODEF) is a format
   for representing computer security information commonly exchanged
   between Computer Security Incident Response Teams (CSIRTs).  It
   provides an XML representation for conveying:

   o  cyber intelligence to characterize threats;

   o  cyber incident reports to document particular cyber security
      events or relationships between events;

   o  cyber event mitigation to request proactive and reactive
      mitigation approaches to cyber intelligence or incidents; and

   o  cyber information sharing meta-data so that these various classes
      of information can be exchanged among parties.

   The data model encodes information about hosts, networks, and the
   services running on these systems; attack methodology and associated
   forensic evidence; impact of the activity; and limited approaches for
   documenting workflow.

   The overriding purpose of the IODEF is to enhance the operational
   capabilities of CSIRTs.  Community adoption of the IODEF provides an
   improved ability to resolve incidents and convey situational
   awareness by simplifying collaboration and data sharing.  This
   structured format provided by the IODEF allows for:

   o  increased automation in processing of incident data, since the
      resources of security analysts to parse free-form textual
      documents will be reduced;

   o  decreased effort in normalizing similar data (even when highly
      structured) from different sources; and

   o  a common format on which to build interoperable tools for incident
      handling and subsequent analysis, specifically when data comes
      from multiple constituencies.

   Coordinating with other CSIRTs is not strictly a technical problem.
   There are numerous procedural, trust, and legal considerations that
   might prevent an organization from sharing information.  The IODEF
   does not attempt to address them.  However, operational
   implementations of the IODEF will need to consider this broader
   context.

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   Sections 3 and 8 specify the IODEF data model with text and an XML
   schema.  The types used by the data model are covered in Section 2.
   Processing considerations, the handling of extensions, and
   internationalization issues related to the data model are covered in
   Sections 4, 5, and 6, respectively.  Examples are listed in
   Section 7.  Section 1 provides the background for the IODEF, and
   Section 9 documents the security considerations.

1.1.  Changes from 5070

   This document contains changes with respect to its predecessor
   RFC5070.

   o  All of the RFC5070 Errata was implemented.

   o  Imported the xmlns:ds namespace to include digital signature hash
      classes.

   o  The following classes were added to IODEF-Document:
      AdditionalData.

   o  The following class and attribute was added to Incident:
      IndicatorData and @status.

   o  The following classes were added to Incident and EventData:
      GenerationTime and Discovery.

   o  The following classes and attributes were added to the Service
      class: EmailData, DomainData, AssetID, ApplicationHeader @virtual,
      and @ownership.  Service@ip_protocol was renamed to @ip-protocol.

   o  The following classes were added to the Record class: HashData and
      WindowsRegistryKeysModified.

   o  The following classes were added to the RelatedActivity class:
      ThreatActor, Campaign, Confidence, Description, and
      AdditionalData.

   o  The following classes were added to Assessment: IncidentCategory,
      SystemImpact, BusinessImpact, IntendedImpact and MitigatingFactor.

   o  The following classes were added to Node: PostalAddress and
      DomainData.  The following classes were removed from Node: Removed
      NodeName and DateTime.

   o  The following classes were added to the Contact class:
      ContactTitle.

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   o  The following classes were added to Expectation and HistoryItem:
      DefinedCOA.

   o  The following classes were added to Service: ServiceName

   o  The following classes were added to Reference: ReferenceName
      (replaced Name).

   o  The following attributes were added to Counter: type and unit.

   o  Additional enumerated values were added to the following
      attributes: @restriction, {Expectation, HistoryItem}@action,
      NodeRole@category, Incident@purpose, Contact@role,
      AdditionalData@dtype, System@spoofed.

   o  Added option for public extension of enumerated attributes with an
      IANA registry and added @ext-restriction.

   o  Removed Impact class in favor of using SystemImpact and
      IncidentCategory.

   o  iodef:MLStringType uses xml:lang and @translation-id.

   o  Incident/ReportTime and Assessment are longer mandatory.

   o  Incident/GenerateTime is mandatory.

1.2.  Terminology

   The key words "MUST," "MUST NOT," "REQUIRED," "SHALL," "SHALL NOT,"
   "SHOULD," "SHOULD NOT," "RECOMMENDED," "MAY," and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

   Definitions for some of the common computer security-related
   terminology used in this document can be found in Section 2 of
   [refs.requirements].

1.3.  Notations

   The normative IODEF data model is specified with the text in
   Section 3 and the XML schema in Section 8.  To help in the
   understanding of the data elements, Section 3 also depicts the
   underlying information model using Unified Modeling Language (UML).
   This abstract presentation of the IODEF is not normative.

   For clarity in this document, the term "XML document" will be used
   when referring generically to any instance of an XML document.  The
   term "IODEF document" will be used to refer to specific elements and

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   attributes of the IODEF schema.  The terms "class" and "element" will
   be used interchangeably to reference either the corresponding data
   element in the information or data models, respectively.

1.4.  About the IODEF Data Model

   The IODEF data model is a data representation that provides a
   framework for sharing information commonly exchanged by CSIRTs about
   computer security incidents.  A number of considerations were made in
   the design of the data model.

   o  The data model serves as a transport format.  Therefore, its
      specific representation is not the optimal representation for on-
      disk storage, long-term archiving, or in-memory processing.

   o  As there is no precise widely agreed upon definition for an
      incident, the data model does not attempt to dictate one through
      its implementation.  Rather, a broad understanding is assumed in
      the IODEF that is flexible enough to encompass most operators.

   o  Describing an incident for all definitions would require an
      extremely complex data model.  Therefore, the IODEF only intends
      to be a framework to convey commonly exchanged incident
      information.  It ensures that there are ample mechanisms for
      extensibility to support organization-specific information, and
      techniques to reference information kept outside of the explicit
      data model.

   o  The domain of security analysis is not fully standardized and must
      rely on free-form textual descriptions.  The IODEF attempts to
      strike a balance between supporting this free-form content, while
      still allowing automated processing of incident information.

   o  The IODEF is only one of several security relevant data
      representations being standardized.  Attempts were made to ensure
      they were complementary.  The data model of the Intrusion
      Detection Message Exchange Format [RFC4765] influenced the design
      of the IODEF.

   Further discussion of the desirable properties for the IODEF can be
   found in the Requirements for the Format for Incident Information
   Exchange (FINE) [refs.requirements].

1.5.  About the IODEF Implementation

   The IODEF implementation is specified as an Extensible Markup
   Language (XML) [W3C.XML] Schema [W3C.SCHEMA].

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   Implementing the IODEF in XML provides numerous advantages.  Its
   extensibility makes it ideal for specifying a data encoding framework
   that supports various character encodings.  Likewise, the abundance
   of related technologies (e.g., XSL, XPath, XML-Signature) makes for
   simplified manipulation.  However, XML is fundamentally a text
   representation, which makes it inherently inefficient when binary
   data must be embedded or large volumes of data must be exchanged.

2.  IODEF Data Types

   The various data elements of the IODEF data model are typed.  This
   section discusses these data types.  When possible, native Schema
   data types were adopted, but for more complicated formats, regular
   expressions (see Appendix F of [W3C.SCHEMA.DTYPES]) or external
   standards were used.

2.1.  Integers

   An integer is represented by the INTEGER data type.  Integer data
   MUST be encoded in Base 10.

   The INTEGER data type is implemented as an "xs:integer" in
   [W3C.SCHEMA.DTYPES].

2.2.  Real Numbers

   Real (floating-point) attributes are represented by the REAL data
   type.  Real data MUST be encoded in Base 10.

   The REAL data type is implemented as an "xs:float" in
   [W3C.SCHEMA.DTYPES].

2.3.  Characters and Strings

   A single character is represented by the CHARACTER data type.  A
   character string is represented by the STRING data type.  Special
   characters must be encoded using entity references.  See Section 4.1.

   The CHARACTER and STRING data types are implemented as an "xs:string"
   in [W3C.SCHEMA.DTYPES].

2.4.  Multilingual Strings

   A character string that needs to be represented in a language
   different than the default encoding of the document is of the
   ML_STRING data type.

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   ML_STRING data type is implemented as the "iodef:MLStringType" type
   in the schema.  This type extends the "xs:string" to include two
   attributes.  The body of any class that uses this type is the
   multilingual string.

   +------------------------+
   | iodef:MLStringType     |
   +------------------------+
   | xs:string              |
   |                        |
   | ENUM xml:lang          |
   | STRING translation-id  |
   +------------------------+

                   Figure 1: The iodef:MLStringType Type

   The content of the class is a character string of type "xs:string"
   whose language MAY be specified by the xml:lang attribute.

   The attributes of the iodef:MLStringType type are:

   xml:lang
      Optional.  ENUM.  A language identifier per Section 2.12 of
      [W3C.XML] whose values and form are described in [RFC5646].  The
      interpretation of this code is described in Section 6.

   translation-id
      Optional.  STRING.  An identifier to relate other instances of
      this class with the same parent as translations of this text.  The
      scope of this identifier is limited to all of the direct, peer
      child classes of a given parent class.

   Using this class enables representing translations of the same text
   in multiple languages.  Each translation is a distinct instance of
   this class with a common parent.  A group of classes each with a
   translated instance of text is related by setting a common identifier
   in the translation-id attribute.  The language of a given class is
   set by the xml:lang attribute.

2.5.  Bytes

   A binary octet is represented by the BYTE data type.  A sequence of
   binary octets is represented by the BYTE[] data type.  These octets
   are encoded using base64.

   The BYTE data type is implemented as an "xs:base64Binary" in
   [W3C.SCHEMA.DTYPES].

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2.6.  Hexadecimal Bytes

   A binary octet is represented by the HEXBIN (and HEXBIN[]) data type.
   This octet is encoded as a character tuple consisting of two
   hexadecimal digits.

   The HEXBIN data type is implemented as an "xs:hexBinary" in
   [W3C.SCHEMA.DTYPES].

2.7.  Enumerated Types

   Enumerated types are represented by the ENUM data type, and consist
   of an ordered list of acceptable values.  Each value has a
   representative keyword.  Within the IODEF schema, the enumerated type
   keywords are used as attribute values.

   The ENUM data type is implemented as a series of "xs:NMTOKEN" in the
   schema.

2.8.  Date-Time String

   Date-Time strings are represented by the DATETIME data type.  Each
   date-time string identifies a particular instant in time.  Ranges are
   not supported.

   Date-time strings are formatted according to a subset of [ISO8601]
   documented in [RFC3339].

   The DATETIME data type is implemented as an "xs:dateTime" in the
   schema.

2.9.  Timezone String

   A timezone offset from UTC is represented by the TIMEZONE data type.
   It is formatted according to the following regular expression:
   "Z|[\+\-](0[0-9]|1[0-4]):[0-5][0-9]".

   The TIMEZONE data type is implemented as an "xs:string" with a
   regular expression constraint in [W3C.SCHEMA.DTYPES].  This regular
   expression is identical to the timezone representation implemented in
   an "xs:dateTime".

2.10.  Port Lists

   A list of network ports are represented by the PORTLIST data type.  A
   PORTLIST consists of a comma-separated list of numbers and ranges
   (N-M means ports N through M, inclusive).  It is formatted according

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   to the following regular expression: "\d+(\-\d+)?(,\d+(\-\d+)?)*".
   For example, "2,5-15,30,32,40-50,55-60".

   The PORTLIST data type is implemented as an "iodef:PortlistType" in
   the schema.

2.11.  Postal Address

   A postal address is represented by the POSTAL data type.  The format
   of the POSTAL data type is documented in Section 2.23 of [RFC4519] as
   a free-form multi-line string separated by the "$" character.

   The POSTAL data type is implemented as an "iodef:MLStringType" in the
   schema.

2.12.  Telephone and Fax Numbers

   A telephone or fax number is represented by the PHONE data type.  The
   format of the PHONE data type is documented in Section 2.35 of
   [RFC4519].

   The PHONE data type is implemented as an "xs:string" in the schema.

2.13.  Email String

   An email address is represented by the EMAIL data type.  The format
   of the EMAIL data type is documented in Section 3.4.1 [RFC5322].

   The EMAIL data type is implemented as an "xs:string" in the schema.

2.14.  Uniform Resource Locator strings

   A uniform resource locator (URL) is represented by the URL data type.
   The format of the URL data type is documented in [RFC3986].

   The URL data type is implemented as an "xs:anyURI" in the schema.

2.15.  Identifiers and Identifier References

   An identifier unique to the Document is represented by the ID data
   type.  A reference to this identifier is represented by the IDREF
   data type.  The acceptable format of ID and IDREF is documented in
   Section 3.3.8 and 3.3.9 of [W3C.SCHEMA.DTYPES].

   The ID and IDREF data types are implemented as "xs:ID" and "xs:IDREF"
   in the schema.

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2.16.  Software

   The SOFTWARE data type describes a particular version of software.
   This description can be made by using a reference, a URL or with
   free-form text.

   +--------------------+
   | iodef:SoftwareType |
   +--------------------+
   |                    |<>--{0..1}--[ SoftwareReference ]
   |                    |<>--{0..*}--[ URL               ]
   |                    |<>--{0..*}--[ Description       ]
   +--------------------+

                      Figure 2: The SoftwareType Type

   The aggregate classes of the SoftwareType type are:

   SoftwareReference
      Zero or one.  Reference to a software application.  See
      Section 2.16.1.

   URL
      Zero or more.  URL.  A URL associated with the application.

   Description
      Zero or more.  ML_STRING.  A free-form text description of this
      application.

   At least one of these classes MUST be present.

   The iodef:SoftwareType type has no attributes.

2.16.1.  SoftwareReference Class

   The SoftwareReference class is a reference to a particular version of
   software.

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   +----------------------+
   | SoftwareReference    |
   +----------------------+
   | xs:any               |
   |                      |
   | ENUM spec-name       |
   | STRING ext-spec-name |
   | ENUM dtype           |
   | STRING enum-dtype    |
   +----------------------+

                   Figure 3: The SoftwareReference Class

   The element content of this type is varies according to the value of
   the spec-name attribute.  This content is defined as "xs:any" in the
   schema.

   The attributes of the SoftwareReference class are:

   spec-name
      Required.  ENUM.  Identifies the format and semantics of the
      element body of this class.  Formal standards and specifications
      can be referenced as well as free-form description with user-
      provided data-types.  These values are maintained in the
      "SoftwareReference-spec-id" IANA registry per Table 1

      1.  custom.  The element content is free-form and of the data type
          specified by the dtype attribute.  If this value is selected,
          then the dtype attribute MUST be set.

      2.  cpe.  The element content describes a Common Platform
          Enumeration (CPE) entry [fix me. reference].

      3.  swid.  The element content describes a software identification
          (SWID) tag per ISO/IEC 19770-2:2009 [fix me. reference].

      4.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-spec-name
      Optional.  STRING.  A means by which to extend the spec-name
      attribute.  See Section 5.1.1.

   dtype
      Optional.  ENUM.  The data type of the element content.  The
      permitted values for this attribute are shown below.  The default

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      value is "string".  These values are maintained in the
      "SoftwareReference-dtype" IANA registry per Table 1.

      1.  bytes.  The element content is of type HEXBIN.

      2.  integer.  The element content is of type INTEGER.

      3.  real.  The element content is of type REAL.

      4.  string.  The element content is of type STRING.

      5.  xml.  The element content is XML.  See Section 5.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-dtype
      Optional.  STRING.  A means by which to extend the dtype
      attribute.  See Section 5.1.1.

2.17.  Extension

   The EXTENSION data type is an extension mechanism for information not
   otherwise represented in the data model.  The data type of the
   extension is described by the dtype attribute.  For simple
   information, atomic data types (e.g., integers, strings) are
   supported.  Their semantics is further described by the meaning and
   formatid attributes.  This data type can also be used to extend the
   data model (and the associated schema) by encapsulating entire XML
   documents conforming to another schema.  A detailed discussion for
   extending the data model and the schema can be found in Section 5.
   Additional coordination may be required to ensure that a recipient of
   a document using this type can parse and process it.

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   +------------------------+
   | iodef:ExtensionType    |
   +------------------------+
   | xs:any                 |
   |                        |
   | STRING name            |
   | ENUM dtype             |
   | STRING ext-dtype       |
   | STRING meaning         |
   | STRING formatid        |
   | ENUM restriction       |
   | STRING ext-restriction |
   | ID observable-id       |
   +------------------------+

                  Figure 4: The iodef:ExtensionType Type

   The element content of this type is the extension being added to the
   data model.  This content is defined as "xs:any" in the schema.

   The attributes of the iodef:ExtensionType type are:

   name
      Optional.  STRING.  A free-form name of the field or data element.

   dtype
      Required.  ENUM.  The data type of the element content.  The
      default value is "string".  These values are maintained in the
      "ExtensionType-dtype" IANA registry per Table 1.

      1.   boolean.  The element content is of type BOOLEAN.

      2.   byte.  The element content is of type BYTE.

      3.   bytes.  The element content is of type HEXBIN.

      4.   character.  The element content is of type CHARACTER.

      5.   date-time.  The element content is of type DATETIME.

      6.   ntpstamp.  Same as date-time.

      7.   integer.  The element content is of type INTEGER.

      8.   portlist.  The element content is of type PORTLIST.

      9.   real.  The element content is of type REAL.

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      10.  string.  The element content is of type STRING.

      11.  file.  The element content is a base64 encoded binary file
           encoded as a BYTE[] type.

      12.  path.  The element content is a file-system path encoded as a
           STRING type.

      13.  frame.  The element content is a layer-2 frame encoded as a
           HEXBIN type.

      14.  packet.  The element content is a layer-3 packet encoded as a
           HEXBIN type.

      15.  ipv4-packet.  The element content is an IPv4 packet encoded
           as a HEXBIN type.

      16.  ipv6-packet.  The element content is an IPv6 packet encoded
           as a HEXBIN type.

      17.  url.  The element content is of type URL.

      18.  csv.  The element content is a common separated value (CSV)
           list per Section 2 of [RFC4180] encoded as a STRING type.

      19.  winreg.  The element content is a Windows registry key
           encoded as a STRING type.

      20.  xml.  The element content is XML.  See Section 5.

      21.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-dtype
      Optional.  STRING.  A means by which to extend the dtype
      attribute.  See Section 5.1.1.

   meaning
      Optional.  STRING.  A free-form description of the element
      content.

   formatid
      Optional.  STRING.  An identifier referencing the format or
      semantics of the element content.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

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   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.  The IODEF Data Model

   In this section, the individual components of the IODEF data model
   will be discussed in detail.  For each class, the semantics will be
   described and the relationship with other classes will be depicted
   with UML.  When necessary, specific comments will be made about
   corresponding definition in the schema in Section 8

3.1.  IODEF-Document Class

   The IODEF-Document class is the top level class in the IODEF data
   model.  All IODEF documents are an instance of this class.

   +--------------------------+
   | IODEF-Document           |
   +--------------------------+
   | STRING version           |<>--{1..*}--[ Incident       ]
   | ENUM xml:lang            |<>--{0..*}--[ AdditionalData ]
   | STRING format-id         |
   | STRING private-enum-name |
   | STRING private-enum-id   |
   +--------------------------+

                      Figure 5: IODEF-Document Class

   The aggregate classes of the IODEF-Document class are:

   Incident
      One or more.  The information related to a single incident.  See
      Section 3.2.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The attributes of the IODEF-Document class are:

   version
      Required.  STRING.  The IODEF specification version number to
      which this IODEF document conforms.  The value of this attribute
      MUST be "2.00"

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   xml:lang
      Optional.  ENUM.  A language identifier per Section 2.12 of
      [W3C.XML] whose values and form are described in [RFC5646].  The
      interpretation of this code is described in Section 6.

   format-id
      Optional.  STRING.  A free-form string to convey processing
      instructions to the recipient of the document.  Its semantics must
      be negotiated out-of-band.

   private-enum-name
      Optional.  STRING.  A globally unique identifier for the CSIRT
      generating the document to deconflict private extensions used in
      the Document.  The fully qualified domain name associated with the
      CSIRT MUST be used as the identifier.

   private-enum-id
      Optional.  STRING.  An organizationally unique identifier for an
      extension used in the Document.  If this attribute is set, the
      private-enum-name MUST also be set.

3.2.  Incident Class

   Every incident is represented by an instance of the Incident class.
   This class provides a standardized representation for commonly
   exchanged incident data.

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   +-------------------------+
   | Incident                |
   +-------------------------+
   | ENUM purpose            |<>----------[ IncidentID      ]
   | STRING ext-purpose      |<>--{0..1}--[ AlternativeID   ]
   | ENUM status             |<>--{0..*}--[ RelatedActivity ]
   | STRING ext-status       |<>--{0..1}--[ DetectTime      ]
   | ENUM xml:lang           |<>--{0..1}--[ StartTime       ]
   | ENUM restriction        |<>--{0..1}--[ EndTime         ]
   | STRING ext-restriction  |<>--{0..1}--{ RecoveryTime    ]
   | ID observable-id        |<>--{0..1}--[ ReportTime      ]
   |                         |<>----------[ GenerationTime  ]
   |                         |<>--{0..*}--[ Description     ]
   |                         |<>--{0..*}  [ Discovery       ]
   |                         |<>--{0..*}--[ Assessment      ]
   |                         |<>--{0..*}--[ Method          ]
   |                         |<>--{1..*}--[ Contact         ]
   |                         |<>--{0..*}--[ EventData       ]
   |                         |<>--{0..1}--[ IndicatorData   ]
   |                         |<>--{0..1}--[ History         ]
   |                         |<>--{0..*}--[ AdditionalData  ]
   +-------------------------+

                       Figure 6: The Incident Class

   The aggregate classes of the Incident class are:

   IncidentID
      One.  An incident tracking number assigned to this incident by the
      CSIRT that generated the IODEF document.  See Section 3.4.

   AlternativeID
      Zero or one.  The incident tracking numbers used by other CSIRTs
      to refer to the incident described in the document.  See
      Section 3.5.

   RelatedActivity
      Zero or more.  Related activity and attribution of this activity.
      See Section 3.6.

   DetectTime
      Zero or one.  DATETIME.  The time the incident was first detected.

   StartTime
      Zero or one.  DATETIME.  The time the incident started.

   EndTime
      Zero or one.  DATETIME.  The time the incident ended.

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   RecoveryTime
      Zero or one.  DATETIME.  The time the site recovered from the
      incident.

   ReportTime
      Zero or one.  DATETIME.  The time the incident was reported.

   GenerationTime
      One.  DATETIME.  The time the content in this Incident class was
      generated.

   Description
      Zero or more.  ML_STRING.  A free-form textual description of the
      incident.

   Discovery
      Zero or more.  The means by which this incident was detected.  See
      Section 3.10.

   Assessment
      Zero or more.  A characterization of the impact of the incident.
      See Section 3.12.

   Method
      Zero or more.  The techniques used by the intruder in the
      incident.  See Section 3.11.

   Contact
      One or more.  Contact information for the parties involved in the
      incident.  See Section 3.9.

   EventData
      Zero or more.  Description of the events comprising the incident.
      See Section 3.14.

   IndicatorData
      Zero or one.  Description of indicators.  See Section 3.28.

   History
      Zero or one.  A log of significant events or actions that occurred
      during the course of handling the incident.  See Section 3.13.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The attributes of the Incident class are:

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   purpose
      Required.  ENUM.  The purpose attribute represents the reason why
      the IODEF document was created.  It is closely related to the
      Expectation class (Section 3.15).  These values are maintained in
      the "Incident-purpose" IANA registry per Table 1.  This attribute
      is defined as an enumerated list:

      1.  traceback.  The document was sent for trace-back purposes.

      2.  mitigation.  The document was sent to request aid in
          mitigating the described activity.

      3.  reporting.  The document was sent to comply with reporting
          requirements.

      4.  watch.  The document was sent to convey indicators to watch
          for particular activity.

      5.  other.  The document was sent for purposes specified in the
          Expectation class.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-purpose
      Optional.  STRING.  A means by which to extend the purpose
      attribute.  See Section 5.1.1.

   status
      Optional.  ENUM.  The status attribute conveys the state in a
      workflow where the incident is currently found.  These values are
      maintained in the "Incident-status" IANA registry per Table 1.
      This attribute is defined as an enumerated list:

      1.  new.  The document is newly reported and has not been
          actioned.

      2.  in-progress.  The contents of this document are under
          investigation.

      3.  forwarded.  The document has been forwarded to another party
          for handling.

      4.  resolved.  The investigation into the activity in this
          document has concluded.

      5.  future.  The described activity has not yet been detected.

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      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-status
      Optional.  STRING.  A means by which to extend the status
      attribute.  See Section 5.1.1.

   xml:lang
      Optional.  ENUM.  A language identifier per Section 2.12 of
      [W3C.XML] whose values and form are described in [RFC5646].  The
      interpretation of this code is described in Section 6.

   restriction
      Optional.  ENUM.  See Section 3.3.1.  The default value is
      "private".

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.3.  Common Attributes

   There are a number of recurring attributes used by the data model.
   They are documented in this section.

3.3.1.  restriction Attribute

   The restriction attribute indicates the disclosure guidelines to
   which the sender expects the recipient to adhere for the information
   represented in this class and its children.  This guideline provides
   no security since there are no specified technical means to ensure
   that the recipient of the document handles the information as the
   sender requested.

   The value of this attribute is logically inherited by the children of
   this class.  That is to say, the disclosure rules applied to this
   class, also apply to its children.

   It is possible to set a granular disclosure policy, since all of the
   high-level classes (i.e., children of the Incident class) have a
   restriction attribute.  Therefore, a child can override the
   guidelines of a parent class, be it to restrict or relax the
   disclosure rules (e.g., a child has a weaker policy than an ancestor;
   or an ancestor has a weak policy, and the children selectively apply

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   more rigid controls).  The implicit value of the restriction
   attribute for a class that did not specify one can be found in the
   closest ancestor that did specify a value.

   This attribute is defined as an enumerated value with a default value
   of "private".  Note that the default value of the restriction
   attribute is only defined in the context of the Incident class.  In
   other classes where this attribute is used, no default is specified.

   These values are maintained in the "Restriction" IANA registry per
   Table 1.

   1.   public.  The information can be freely distributed without
        restriction.

   2.   partner.  The information may be shared within a closed
        community of peers, partners, or affected parties, but cannot be
        openly published.

   3.   need-to-know.  The information may be shared only within the
        organization with individuals that have a need to know.

   4.   private.  The information may not be shared.

   5.   default.  The information can be shared according to an
        information disclosure policy pre-arranged by the communicating
        parties.

   6.   white.  Same as 'public'.

   7.   green.  Same as 'partner'.

   8.   amber.  Same as 'need-to-know'.

   9.   red.  Same as 'private'.

   10.  ext-value.  A value used to indicate that this attribute is
        extended and the actual value is provided using the
        corresponding ext-* attribute.  See Section 5.1.1.

3.3.2.  observable-id Attribute

   Information included in an incident report may be an observable
   relevant to an indicator.  The observable-id attribute provides a
   unique identifier in the scope of the document for this observable.
   This identifier can then be used to reference the observable with an
   ObservableReference class to define an indicator in the IndicatorData
   class.

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3.4.  IncidentID Class

   The IncidentID class represents an incident tracking number that is
   unique in the context of the CSIRT and identifies the activity
   characterized in an IODEF Document.  This identifier would serve as
   an index into the CSIRT incident handling system.  The combination of
   the name attribute and the string in the element content MUST be a
   globally unique identifier describing the activity.  Documents
   generated by a given CSIRT MUST NOT reuse the same value unless they
   are referencing the same incident.

   +------------------------+
   | IncidentID             |
   +------------------------+
   | STRING                 |
   |                        |
   | STRING name            |
   | STRING instance        |
   | ENUM restriction       |
   | STRING ext-restriction |
   +------------------------+

                      Figure 7: The IncidentID Class

   The content of the class is an incident identifier of type STRING.

   The attributes of the IncidentID class are:

   name
      Required.  STRING.  An identifier describing the CSIRT that
      created the document.  In order to have a globally unique CSIRT
      name, the fully qualified domain name associated with the CSIRT
      MUST be used.

   instance
      Optional.  STRING.  An identifier referencing a subset of the
      named incident.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

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3.5.  AlternativeID Class

   The AlternativeID class lists the incident tracking numbers used by
   CSIRTs, other than the one generating the document, to refer to the
   identical activity described in the IODEF document.  A tracking
   number listed as an AlternativeID references the same incident
   detected by another CSIRT.  The incident tracking numbers of the
   CSIRT that generated the IODEF document must never be considered an
   AlternativeID.

   +------------------------+
   | AlternativeID          |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ IncidentID ]
   | STRING ext-restriction |
   +------------------------+

                     Figure 8: The AlternativeID Class

   The aggregate class of the AlternativeID class is:

   IncidentID
      One or more.  The incident tracking number of another CSIRT.  See
      Section 3.4.

   The attributes of the AlternativeID class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.6.  RelatedActivity Class

   The RelatedActivity class relates the information described in the
   rest of the IODEF document to previously observed incidents or
   activity; and allows attribution to a specific actor or campaign.

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   +------------------------+
   | RelatedActivity        |
   +------------------------+
   | ENUM restriction       |<>--{0..*}--[ IncidentID     ]
   | STRING ext-restriction |<>--{0..*}--[ URL            ]
   |                        |<>--{0..*}--[ ThreatActor    ]
   |                        |<>--{0..*}--[ Campaign       ]
   |                        |<>--{0..1}--[ Confidence     ]
   |                        |<>--{0..*}--[ Description    ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                      Figure 9: RelatedActivity Class

   The aggregate classes of the RelatedActivity class are:

   IncidentID
      Zero or more.  The incident tracking number of a related incident.
      See Section 3.4.

   URL
      Zero or more.  URL.  A URL to activity related to this incident.

   ThreatActor
      Zero or more.  The threat actor to whom the described activity is
      attributed.  See Section 3.7.

   Campaign
      Zero or more.  The campaign of a given threat actor to whom the
      described activity is attributed.  See Section 3.8.

   Confidence
      Zero or one.  An estimate of the confidence in attributing this
      RelatedActivity to the event described in the document.  See
      Section 3.12.5.

   Description
      Zero or more.  ML_STRING.  A description of how these
      relationships were derived.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   RelatedActivity MUST at least have one instance of a child class.

   The attributes of the RelatedActivity class are:

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   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.7.  ThreatActor Class

   The ThreatActor class describes a given actor.

   +------------------------+
   | ThreatActor            |
   +------------------------+
   | ENUM restriction       |<>--{0..*}--[ ThreatActorID  ]
   | STRING ext-restriction |<>--{0..*}--[ URL            ]
   |                        |<>--{0..*}--[ Description    ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                       Figure 10: ThreatActor Class

   The aggregate classes of the ThreatActor class are:

   ThreatActorID
      Zero or more.  STRING.  An identifier for the ThreatActor.

   URL
      Zero or more.  URL.  A URL associated with the ThreatActor.

   Description
      Zero or more.  ML_STRING.  A description of the ThreatActor.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   ThreatActor MUST have at least one instance of a child class.

   The attributes of the ThreatActor class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

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3.8.  Campaign Class

   The Campaign class describes a campaign of attacks by a threat actor.

   +------------------------+
   | Campaign               |
   +------------------------+
   | ENUM restriction       |<>--{0..*}--[ CampaignID     ]
   | STRING ext-restriction |<>--{0..*}--[ Description    ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                         Figure 11: Campaign Class

   The aggregate classes of the Campaign class are:

   CampaignID
      Zero or more.  STRING.  An identifier for the Campaign.

   Description
      Zero or more.  ML_STRING.  A description of the Campaign.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   Campaign MUST have at least one instance of a Campaign or
   Description.

   The attributes of the Campaign class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.9.  Contact Class

   The Contact class describes contact information for organizations and
   personnel involved in the incident.  This class allows for the naming
   of the involved party, specifying contact information for them, and
   identifying their role in the incident.

   People and organizations are treated interchangeably as contacts; one
   can be associated with the other using the recursive definition of
   the class (the Contact class is aggregated into the Contact class).

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   The 'type' attribute disambiguates the type of contact information
   being provided.

   The inheriting definition of Contact provides a way to relate
   information without requiring the explicit use of identifiers in the
   classes or duplication of data.  A complete point of contact is
   derived by a particular traversal from the root Contact class to the
   leaf Contact class.  As such, multiple points of contact might be
   specified in a single instance of a Contact class.  Each child
   Contact class logically inherits contact information from its
   ancestors.

   +------------------------+
   | Contact                |
   +------------------------+
   | ENUM role              |<>--{0..*}--[ ContactName    ]
   | STRING ext-role        |<>--{0..*}--[ ContactTitle   ]
   | ENUM type              |<>--{0..*}--[ Description    ]
   | STRING ext-type        |<>--{0..*}--[ RegistryHandle ]
   | ENUM restriction       |<>--{0..1}--[ PostalAddress  ]
   | STRING ext-restriction |<>--{0..*}--[ Email          ]
   |                        |<>--{0..*}--[ Telephone      ]
   |                        |<>--{0..1}--[ Timezone       ]
   |                        |<>--{0..*}--[ Contact        ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                       Figure 12: The Contact Class

   The aggregate classes of the Contact class are:

   ContactName
      Zero or more.  ML_STRING.  The name of the contact.  The contact
      may either be an organization or a person.  The type attribute
      disambiguates the semantics.

   ContactTitle
      Zero or more.  ML_STRING.  The title for the individual named in
      the ContactName.

   Description
      Zero or more.  ML_STRING.  A free-form description of this
      contact.  In the case of a person, this is often the
      organizational title of the individual.

   RegistryHandle
      Zero or more.  A handle name into the registry of the contact.
      See Section 3.9.1.

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   PostalAddress
      Zero or more.  The postal address of the contact.  See
      Section 3.9.2.

   Email
      Zero or more.  The email address of the contact.  See
      Section 3.9.3.

   Telephone
      Zero or more.  The telephone number of the contact.  See
      Section 3.9.4.

   Timezone
      Zero or one.  TIMEZONE.  The timezone in which the contact resides
      formatted according to Section 2.9.

   Contact
      Zero or more.  A Contact instance contained within another Contact
      instance inherits the values of the parent(s).  This recursive
      definition can be used to group common data pertaining to multiple
      points of contact and is especially useful when listing multiple
      contacts at the same organization.  See Section 3.9.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   At least one of the aggregate classes MUST be present in an instance
   of the Contact class.  This is not enforced in the IODEF schema as
   there is no simple way to accomplish it.

   The attributes of the Contact class are:

   role
      Required.  ENUM.  Indicates the role the contact fulfills.  This
      attribute is defined as an enumerated list.  These values are
      maintained in the "Contact-role" IANA registry per Table 1.

      1.   creator.  The entity that generate the document.

      2.   reporter.  The entity that reported the information.

      3.   admin.  An administrative contact or business owner for an
           asset or organization.

      4.   tech.  An entity responsible for the day-to-day management of
           technical issues for an asset or organization.

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      5.   provider.  An external hosting provider for an asset.

      6.   zone.  An entity with authority over a DNS zone.

      7.   user.  An end-user of an asset or part of an organization.

      8.   billing.  An entity responsible for billing issues for an
           asset or organization.

      9.   legal.  An entity responsible for legal issue related to an
           asset or organization.

      10.  irt.  An entity responsible for handling security issues for
           an asset or organization.

      11.  abuse.  An entity responsible for handling abuse originating
           from an asset or organization.

      12.  cc.  An entity that is to be kept informed about the events
           related to an asset or organization.

      13.  cc-irt.  A CSIRT or information sharing organization
           coordinating activity related to an asset or organization.

      14.  leo.  A law enforcement organization supporting the
           investigation of activity affecting an asset or organization.

      15.  vendor.  The vendor that produces an asset.

      16.  vendor-support.  A vendor that provides services.

      17.  victim.  A victim in the incident.

      18.  victim-notified.  A victim in the incident who has been
           notified.

      19.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-role
      Optional.  STRING.  A means by which to extend the role attribute.
      See Section 5.1.1.

   type
      Required.  ENUM.  Indicates the type of contact being described.
      This attribute is defined as an enumerated list.  These values are
      maintained in the "Contact-type" IANA registry per Table 1.

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      1.  person.  The information for this contact references an
          individual.

      2.  organization.  The information for this contact references an
          organization.

      3.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.9.1.  RegistryHandle Class

   The RegistryHandle class represents a handle into an Internet
   registry or community-specific database.

   +---------------------+
   | RegistryHandle      |
   +---------------------+
   | STRING              |
   |                     |
   | ENUM registry       |
   | STRING ext-registry |
   +---------------------+

                    Figure 13: The RegistryHandle Class

   The content of the class is a handle into a registry of type STRING.

   The attributes of the RegistryHandle class are:

   registry
      Required.  ENUM.  The database to which the handle belongs.  These
      values are maintained in the "RegistryHandle-registry" IANA
      registry per Table 1.  The possible values are:

      1.  internic.  Internet Network Information Center

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      2.  apnic.  Asia Pacific Network Information Center

      3.  arin.  American Registry for Internet Numbers

      4.  lacnic.  Latin-American and Caribbean IP Address Registry

      5.  ripe.  Reseaux IP Europeens

      6.  afrinic.  African Internet Numbers Registry

      7.  local.  A database local to the CSIRT

      8.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-registry
      Optional.  STRING.  A means by which to extend the registry
      attribute.  See Section 5.1.1.

3.9.2.  PostalAddress Class

   The PostalAddress class specifies an postal address and associated
   annotation.

   +--------------------+
   | PostalAddress      |
   +--------------------+
   | ENUM type          |<>----------[ PAddress         ]
   | STRING ext-type    |<>--{0..*}--[ Description      ]
   +--------------------+

                    Figure 14: The PostalAddress Class

   The aggregate classes of the PostalAddress class are:

   PAddress
      One.  POSTAL.  A postal address.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      address.

   The attributes of the PostalAddress class are:

   type

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      Optional.  ENUM.  Categorizes the type of address described in the
      PAddress class.  These values are maintained in the
      "PostalAddress-type" IANA registry per Table 1.

      1.  street.  An address describing a physical location.

      2.  mailing.  An address to which correspondence should be sent.

      3.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.9.3.  Email Class

   The Email class specifies an email address and associated annotation.

   +--------------------+
   | Email              |
   +--------------------+
   | ENUM type          |<>----------[ EmailTo          ]
   | STRING ext-type    |<>--{0..*}--[ Description      ]
   +--------------------+

                        Figure 15: The Email Class

   The aggregate classes of the Email class are:

   EmailTo
      One.  EMAIL.  An email address.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      email address.

   The attributes of the Email class are:

   type
      Optional.  ENUM.  Categorizes the type of email address described
      in the EmailTo class.  These values are maintained in the "Email-
      type" IANA registry per Table 1.

      1.  direct.  A email address of an individual.

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      2.  hotline.  A email address regularly monitored for operational
          purposes.

      3.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.9.4.  Telephone Class

   The Telephone class describes a telephone number and associated
   annotation.

   +--------------------+
   | Telephone          |
   +--------------------+
   | ENUM type          |<>----------[ TelephoneNumber  ]
   | STRING ext-type    |<>--{0..*}--[ Description      ]
   +--------------------+

                      Figure 16: The Telephone Class

   The aggregate classes of the Telephone class are:

   TelephoneNumber
      One.  PHONE.  A telephone number.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      phone number.

   The attributes of the Telephone class are:

   type
      Optional.  ENUM.  Categorizes the type of telephone number
      described in the TelephoneNumber class.  These values are
      maintained in the "Telephone-type" IANA registry per Table 1.

      1.  direct.  A number at an individual.

      2.  mobile.  A number of a mobile phone.

      3.  fax.  A number to a fax machine.

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      4.  hotline.  A number to a regularly monitored operational
          hotline.

      5.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.10.  Discovery Class

   The Discovery class describes how an incident was detected.

   +------------------------+
   | Discovery              |
   +------------------------+
   | ENUM source            |<>--{0..*}--[ Description      ]
   | STRING ext-source      |<>--{0..*}--[ Contact          ]
   | ENUM restriction       |<>--{0..*}--[ DetectionPattern ]
   | STRING ext-restriction |
   +------------------------+

                      Figure 17: The Discovery Class

   The aggregate classes of the Discovery class are:

   Description
      Zero or more.  ML_STRING.  A free-form text description of how
      this incident was detected.

   Contact
      Zero or more.  Contact information for the party that discovered
      the incident.  See Section 3.9.

   DetectionPattern
      Zero or more.  Describes an application-specific configuration
      that detected the incident.  See Section 3.10.1.

   The attributes of the Discovery class are:

   source
      Optional.  ENUM.  Categorizes the techniques used to discover the
      incident.  These values are partially derived from Table 3-1 of
      [NIST800.61rev2].  These values are maintained in the "Discovery-
      source" IANA registry per Table 1.

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      1.   nidps.  Network Intrusion Detection or Prevention system.

      2.   hips.  Host-based Intrusion Prevention system.

      3.   siem.  Security Information and Event Management System.

      4.   av.  Antivirus or and antispam software.

      5.   third-party-monitoring.  Contracted third-party monitoring
           service.

      6.   incident.  The activity was discovered while investigating an
           unrelated incident.

      7.   os-log.  Operating system logs.

      8.   application-log.  Application logs.

      9.   device-log.  Network device logs.

      10.  network-flow.  Network flow analysis.

      11.  passive-dns.  Passive DNS analysis.

      12.  investigation.  Manual investigation initiated based on
           notification of a new vulnerability or exploit.

      13.  audit.  Security audit.

      14.  internal-notification.  A party within the organization
           reported the activity

      15.  external-notification.  A party outside of the organization
           reported the activity.

      16.  leo.  A law enforcement organization notified the victim
           organization.

      17.  partner.  A customer or business partner reported the
           activity to the victim organization.

      18.  actor.  The threat actor directly or indirectly reported this
           activity to the victim organization.

      19.  unknown.  Unknown detection approach.

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      20.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-source
      Optional.  STRING.  A means by which to extend the source
      attribute.  See Section 5.1.1.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.10.1.  DetectionPattern Class

   The DetectionPattern class describes a configuration or signature
   that can be used by an IDS/IPS, SIEM, anti-virus, end-point
   protection, network analysis, malware analysis, or host forensics
   tool to identify a particular phenomenon.  This class requires the
   identification of the target application and allows the configuration
   to be describes in either free-form or machine readable form.

   +------------------------+
   | DetectionPattern       |
   +------------------------+
   | ENUM restriction       |<>----------[ Application            ]
   | STRING ext-restriction |<>--{0..*}--[ Description            ]
   |                        |<>--{0..*}--[ DetectionConfiguration ]
   +------------------------+

                   Figure 18: The DetectionPattern Class

   The aggregate classes of the DetectionPattern class are:

   Application
      One.  SOFTWARE.  The application for which the
      DetectionConfiguration or Description is being provided.

   Description
      Zero or more.  ML_STRING.  A free-form text description of how to
      use the Application or provided DetectionConfiguration.

   DetectionConfiguration
      Zero or more.  STRING.  A machine consumable configuration to find
      a pattern of activity.

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   Either an instance of the Description or DetectionConfiguration class
   MUST be present.

   The attributes of the DetectionPattern class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.11.  Method Class

   The Method class describes the tactics, techniques, procedures or
   underlying issue used by the intruder in the incident.  This class
   consists of both a list of references describing the attack methods
   and weaknesses and a free form description.

   +------------------------+
   | Method                 |
   +------------------------+
   | ENUM restriction       |<>--{0..*}--[ Reference         ]
   | STRING ext-restriction |<>--{0..*}--[ Description       ]
   |                        |<>--{0..*}--[ sci:AttackPattern ]
   |                        |<>--{0..*}--[ sci:Vulnerability ]
   |                        |<>--{0..*}--[ sci:Weakness      ]
   |                        |<>--{0..*}--[ AdditionalData    ]
   +------------------------+

                        Figure 19: The Method Class

   The aggregate classes of the Method class are:

   Reference
      Zero or more.  A reference to a vulnerability, malware sample,
      advisory, or analysis of an attack technique.  See Section 3.11.1.

   Description
      Zero or more.  ML_STRING.  A free-form text description of
      techniques, tactics, or procedures used by the intruder.

   sci:AttackPattern
      Zero or more.  A reference to an pattern of attack or exploitation
      per [RFC-SCI]

   sci:Vulnerability
      Zero or more.  A reference to a vulnerability per [RFC-SCI]

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   sci:Weakness
      Zero or more.  A reference to the exploited weakness per [RFC-SCI]

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   An instance of one of these child MUST be present.

   The attributes of the Method class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.11.1.  Reference Class

   The Reference class is an external reference to relevant information
   such a vulnerability, IDS alert, malware sample, advisory, or attack
   technique.  A reference consists of a name, a URL to this reference,
   and an optional description.

   +-------------------------+
   | Reference               |
   +-------------------------+
   | ID observable-id        |<>--{0..1}--[ enum:ReferenceName ]
   |                         |<>--{0..*}--[ URL                ]
   |                         |<>--{0..*}--[ Description        ]
   +-------------------------+

                      Figure 20: The Reference Class

   The aggregate classes of the Reference class are:

   enum:ReferenceName
      Zero or one.  Reference identifier per [RFC-ENUM].

   URL
      Zero or more.  URL.  A URL associated with the reference.

   Description
      Zero or more.  ML_STRING.  A free-form text description of this
      reference.

   At least one of these classes MUST be present.

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   The attribute of the Reference class is:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.12.  Assessment Class

   The Assessment class describes the repercussions of the incident to
   the victim.

   +-------------------------+
   | Assessment              |
   +-------------------------+
   | ENUM occurrence         |<>--{0..*}--[ IncidentCategory ]
   | ENUM restriction        |<>--{0..*}--[ SystemImpact     ]
   | STRING ext-restriction  |<>--{0..*}--[ BusinessImpact   ]
   | ID observable-id        |<>--{0..*}--[ TimeImpact       ]
   |                         |<>--{0..*}--[ MonetaryImpact   ]
   |                         |<>--{0..*}--[ IntendedImpact   ]
   |                         |<>--{0..*}--[ Counter          ]
   |                         |<>--{0..*}--[ MitigatingFactor ]
   |                         |<>--{0..*}--[ Cause            ]
   |                         |<>--{0..1}--[ Confidence       ]
   |                         |<>--{0..*}--[ AdditionalData   ]
   +-------------------------+

                        Figure 21: Assessment Class

   The aggregate classes of the Assessment class are:

   IncidentCategory
      Zero or more.  ML_STRING.  A free-form text description
      categorizing the type of Incident.

   SystemImpact
      Zero or more.  Technical characterization of the impact of the
      activity on the victim's enterprise.  See Section 3.12.1.

   BusinessImpact
      Zero or more.  Impact of the activity on the business functions of
      the victim organization.  See Section 3.12.2.

   TimeImpact
      Zero or more.  Impact of the activity measured with respect to
      time.  See Section 3.12.3.

   MonetaryImpact

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      Zero or more.  Impact of the activity measured with respect to
      financial loss.  See Section 3.12.4.

   IntendedImpact
      Zero or more.  Intended impact to the victim by the attacker.
      Defined identically to the BusinessImpact defined in
      Section 3.12.2, but describes intent rather than the realized
      impact.

   Counter
      Zero or more.  A counter with which to summarize the magnitude of
      the activity.  See Section 3.18.3.

   MitigatingFactor
      Zero or more.  ML_STRING.  A description of a mitigating factor an
      impact.

   Cause
      Zero or more.  ML_STRING.  A description of the underlying cause
      of the impact.

   Confidence
      Zero or one.  An estimate of confidence in the assessment.  See
      Section 3.12.5.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   A least one instance of the possible five impact classes (i.e.,
   SystemImpact, BusinessImpact, TimeImpact, MonetaryImpact or
   IntendedImpact) MUST be present.

   The attributes of the Assessment class are:

   occurrence
      Optional.  ENUM.  Specifies whether the assessment is describing
      actual or potential outcomes.

      1.  actual.  This assessment describes activity that has occurred.

      2.  potential.  This assessment describes potential activity that
          might occur.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction

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      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.12.1.  SystemImpact Class

   The SystemImpact class describes the technical impact of the incident
   to the systems on the network.

   +-----------------------+
   | SystemImpact          |
   +-----------------------+
   | ENUM severity         |<>--{0..*}--[ Description ]
   | ENUM completion       |
   | ENUM type             |
   | STRING ext-type       |
   +-----------------------+

                       Figure 22: SystemImpact Class

   The aggregate class of the SystemImpact class is:

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      impact to the system.

   The attributes of the SystemImpact class are:

   severity
      Optional.  ENUM.  An estimate of the relative severity of the
      activity.  The permitted values are shown below.  There is no
      default value.

      1.  low.  Low severity

      2.  medium.  Medium severity

      3.  high.  High severity

   completion
      Optional.  ENUM.  An indication whether the described activity was
      successful.  The permitted values are shown below.  There is no
      default value.

      1.  failed.  The attempted activity was not successful.

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      2.  succeeded.  The attempted activity succeeded.

   type
      Required.  ENUM.  Classifies the impact.  The permitted values are
      shown below.  The default value is "unknown".  These values are
      maintained in the "SystemImpact-type" IANA registry per Table 1.

      1.   takeover-account.  Control was taken of a given account
           (e.g., a social media account).

      2.   takeover-service.  Control was taken of a given service.

      3.   takeover-system.  Control was taken of a given system.

      4.   cps-manipulation.  A cyber physical system was manipulated.

      5.   cps-damage.  A cyber physical system was damaged.

      6.   availability-data.  Access to particular data was degraded or
           denied.

      7.   availability-account.  Access to an account was degraded or
           denied.

      8.   availability-service.  Access to a service was degraded or
           denied.

      9.   availability-system.  Access to a system was degraded or
           denied.

      10.  damaged-system.  Hardware on a system was irreparably
           damaged.

      11.  damaged-data.  Data on a system was deleted.

      12.  breach-proprietary.  Sensitive or proprietary information was
           accessed or exfiltrated.

      13.  breach-privacy.  Personally identifiable information was
           accessed or exfiltrated.

      14.  breach-credential.  Credential information was accessed or
           exfiltrated.

      15.  breach-configuration.  System configuration or data inventory
           was access or exfiltrated.

      16.  integrity-data.  Data on the system was modified.

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      17.  integrity-configuration.  Application or system configuration
           was modified.

      18.  integrity-hardware.  Firmware of a hardware component was
           modified.

      19.  traffic-redirection.  Network traffic on the system was
           redirected

      20.  monitoring-traffic.  Network traffic emerging from a host was
           monitored.

      21.  monitoring-host.  System activity (e.g., running processes,
           keystrokes) were monitored.

      22.  policy.  Activity violated the system owner's acceptable use
           policy.

      23.  unknown.  The impact is unknown.

      24.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.12.2.  BusinessImpact Class

   The BusinessImpact class describes and characterizes the degree to
   which the function of the organization was impacted by the Incident.

   +-------------------------+
   | BusinessImpact          |
   +-------------------------+
   | ENUM severity           |<>--{0..*}--[ Description ]
   | STRING ext-severity     |
   | ENUM type               |
   | STRING ext-type         |
   +-------------------------+

                      Figure 23: BusinessImpact Class

   The aggregate class of the BusinessImpact class is:

   Description

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      Zero or more.  ML_STRING.  A free-form text description of the
      impact to the organization.

   The attributes of the BusinessImpact class are:

   xml:lang
      Optional.  ENUM.  A language identifier per Section 2.12 of
      [W3C.XML] whose values and form are described in [RFC5646].  The
      interpretation of this code is described in Section 6.

   translation-id
      Optional.  STRING.  An identifier to relate other instances of
      this class as translations of this text.  See Section 6.

   severity
      Optional.  ENUM.  Characterizes the severity of the incident on
      business functions.  The permitted values are shown below.  They
      were derived from Table 3-2 of [NIST800.61rev2].  The default
      value is "unknown".  These values are maintained in the
      "BusinessImpact-severity" IANA registry per Table 1.

      1.  none.  No effect to the organization's ability to provide all
          services to all users.

      2.  low.  Minimal effect as the organization can still provide all
          critical services to all users but has lost efficiency.

      3.  medium.  The organization has lost the ability to provide a
          critical service to a subset of system users.

      4.  high.  The organization is no longer able to provide some
          critical services to any users.

      5.  unknown.  The impact is not known.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-severity
      Optional.  STRING.  A means by which to extend the severity
      attribute.  See Section 5.1.1.

   type
      Required.  ENUM.  Characterizes the effect this incident had on
      the business.  The permitted values are shown below.  The default
      value is "unknown".  These values are maintained in the
      "BusinessImpact-type" IANA registry per Table 1.

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      1.   breach-proprietary.  Sensitive or proprietary information was
           accessed or exfiltrated.

      2.   breach-privacy.  Personally identifiable information was
           accessed or exfiltrated.

      3.   breach-credential.  Credential information was accessed or
           exfiltrated.

      4.   loss-of-integrity.  Sensitive or proprietary information was
           changed or deleted.

      5.   loss-of-service.  Service delivery was disrupted.

      6.   theft-financial.  Money was stolen.

      7.   theft-service.  Services were misappropriated.

      8.   degraded-reputation.  The reputation of the organization's
           brand was diminished.

      9.   asset-damage.  A cyber-physical system was damaged.

      10.  asset-manipulation.  A cyber-physical system was manipulated.

      11.  legal.  The incident resulted in legal or regulatory action.

      12.  extortion.  The incident resulted in actors extorting the
           victim organization.

      13.  unknown.  The impact is unknown.

      14.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.12.3.  TimeImpact Class

   The TimeImpact class describes the impact of the incident on an
   organization as a function of time.  It provides a way to convey down
   time and recovery time.

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   +---------------------+
   | TimeImpact          |
   +---------------------+
   | REAL                |
   |                     |
   | ENUM severity       |
   | ENUM metric         |
   | STRING ext-metric   |
   | ENUM duration       |
   | STRING ext-duration |
   +---------------------+

                        Figure 24: TimeImpact Class

   The content of the class is a positive, floating point number of type
   REAL specifying a unit of time.  The duration and metric attributes
   will imply the semantics.

   The attributes of the TimeImpact class are:

   severity
      Optional.  ENUM.  An estimate of the relative severity of the
      activity.  The permitted values are shown below.  There is no
      default value.

      1.  low.  Low severity

      2.  medium.  Medium severity

      3.  high.  High severity

   metric
      Required.  ENUM.  Defines the metric in which the time is
      expressed.  The permitted values are shown below.  There is no
      default value.  These values are maintained in the "TimeImpact-
      metric" IANA registry per Table 1.

      1.  labor.  Total staff-time to recovery from the activity (e.g.,
          2 employees working 4 hours each would be 8 hours).

      2.  elapsed.  Elapsed time from the beginning of the recovery to
          its completion (i.e., wall-clock time).

      3.  downtime.  Duration of time for which some provided service(s)
          was not available.

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      4.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-metric
      Optional.  STRING.  A means by which to extend the metric
      attribute.  See Section 5.1.1.

   duration
      Optional.  ENUM.  Defines a unit of time, that when combined with
      the metric attribute, fully describes a metric of impact that will
      be conveyed in the element content.  The permitted values are
      shown below.  The default value is "hour".  These values are
      maintained in the "TimeImpact-duration" IANA registry per Table 1.

      1.  second.  The unit of the element content is seconds.

      2.  minute.  The unit of the element content is minutes.

      3.  hour.  The unit of the element content is hours.

      4.  day.  The unit of the element content is days.

      5.  month.  The unit of the element content is months.

      6.  quarter.  The unit of the element content is quarters.

      7.  year.  The unit of the element content is years.

      8.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-duration
      Optional.  STRING.  A means by which to extend the duration
      attribute.  See Section 5.1.1.

3.12.4.  MonetaryImpact Class

   The MonetaryImpact class describes the financial impact of the
   activity on an organization.  For example, this impact may consider
   losses due to the cost of the investigation or recovery, diminished
   productivity of the staff, or a tarnished reputation that will affect
   future opportunities.

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   +------------------+
   | MonetaryImpact   |
   +------------------+
   | REAL             |
   |                  |
   | ENUM severity    |
   | STRING currency  |
   +------------------+

                      Figure 25: MonetaryImpact Class

   The content of the class is a positive, floating point number of type
   REAL specifying a unit of currency described in the currency
   attribute.

   The attributes of the MonetaryImpact class are:

   severity
      Optional.  ENUM.  An estimate of the relative severity of the
      activity.  The permitted values are shown below.  There is no
      default value.

      1.  low.  Low severity

      2.  medium.  Medium severity

      3.  high.  High severity

   currency
      Optional.  STRING.  Defines the currency in which the monetary
      impact is expressed.  The permitted values are defined in "Codes
      for the representation of currencies and funds" of [ISO4217].
      There is no default value.

3.12.5.  Confidence Class

   The Confidence class represents a best estimate of the validity and
   accuracy of the described impact (see Section 3.12) of the incident
   activity.  This estimate can be expressed as a category or a numeric
   calculation.

   This class if based upon [RFC4765].

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   +------------------+
   | Confidence       |
   +------------------+
   | REAL             |
   |                  |
   | ENUM rating      |
   +------------------+

                        Figure 26: Confidence Class

   The content of the class is a numerical assessment in the confidence
   of the data of type REAL when the value of the rating attribute is
   "numeric".  Otherwise, this element MUST be empty.

   The attribute of the Confidence class is:

   rating
      Required.  ENUM.  A rating of the analytical validity of the
      specified Assessment.  The permitted values are shown below.
      There is no default value.

      1.  low.  Low confidence in the validity.

      2.  medium.  Medium confidence in the validity.

      3.  high.  High confidence in the validity.

      4.  numeric.  The element content contains a number that conveys
          the confidence of the data.  The semantics of this number
          outside the scope of this specification.

      5.  unknown.  The confidence rating value is not known.

3.13.  History Class

   The History class is a log of the significant events or actions
   performed by the involved parties during the course of handling the
   incident.

   The level of detail maintained in this log is left up to the
   discretion of those handling the incident.

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   +------------------------+
   | History                |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ HistoryItem ]
   | STRING ext-restriction |
   +------------------------+

                       Figure 27: The History Class

   The aggregate classes of the History class are:

   HistoryItem
      One or more.  Entry in the history log of significant events or
      actions performed by the involved parties.  See Section 3.13.1.

   The attributes of the History class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.  The default value is
      "default".

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.13.1.  HistoryItem Class

   The HistoryItem class is an entry in the History (Section 3.13) log
   that documents a particular action or event that occurred in the
   course of handling the incident.  The details of the entry are a
   free-form description, but each can be categorized with the type
   attribute.

   +-------------------------+
   | HistoryItem             |
   +-------------------------+
   | ENUM action             |<>----------[ DateTime       ]
   | STRING ext-action       |<>--{0..1}--[ IncidentId     ]
   | ENUM restriction        |<>--{0..1}--[ Contact        ]
   | STRING ext-restriction  |<>--{0..*}--[ Description    ]
   | ID observable-id        |<>--{0..*}--[ DefinedCOA     ]
   |                         |<>--{0..*}--[ AdditionalData ]
   +-------------------------+

                       Figure 28: HistoryItem Class

   The aggregate classes of the HistoryItem class are:

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   DateTime
      One.  DATETIME.  Timestamp of this entry in the history log (e.g.,
      when the action described in the Description was taken).

   IncidentID
      Zero or One.  In a history log created by multiple parties, the
      IncidentID provides a mechanism to specify which CSIRT created a
      particular entry and references this organization's incident
      tracking number.  When a single organization is maintaining the
      log, this class can be ignored.  See Section 3.4.

   Contact
      Zero or One.  Provides contact information for the person that
      performed the action documented in this class.  See Section 3.9.

   Description
      Zero or more.  ML_STRING.  A free-form textual description of the
      action or event.

   DefinedCOA
      Zero or more.  ML_STRING.  A unique identifier meaningful to the
      sender and recipient of this document that references a course of
      action.  This class MUST be present if the action attribute is set
      to "defined-coa".

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   The attributes of the HistoryItem class are:

   action
      Required.  ENUM.  Classifies a performed action or occurrence
      documented in this history log entry.  As activity will likely
      have been instigated either through a previously conveyed
      expectation or internal investigation, this attribute is identical
      to the action attribute of the Expectation class.  The difference
      is only one of tense.  When an action is in this class, it has
      been completed.  See Section 3.15.

   ext-action
      Optional.  STRING.  A means by which to extend the action
      attribute.  See Section 5.1.1.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction

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      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.14.  EventData Class

   The EventData class describes a particular event of the incident for
   a given set of hosts or networks.  This description includes the
   systems from which the activity originated and those targeted, an
   assessment of the techniques used by the intruder, the impact of the
   activity on the organization, and any forensic evidence discovered.

   +-------------------------+
   | EventData               |
   +-------------------------+
   | ENUM restriction        |<>--{0..*}--[ Description    ]
   | STRING ext-restriction  |<>--{0..1}--[ DetectTime     ]
   | ID observable-id        |<>--{0..1}--[ StartTime      ]
   |                         |<>--{0..1}--[ EndTime        ]
   |                         |<>--{0..1}--[ RecoveryTime   ]
   |                         |<>--{0..1}--[ ReportTime     ]
   |                         |<>--{0..*}--[ Contact        ]
   |                         |<>--{0..*}--[ Discovery      ]
   |                         |<>--{0..1}--[ Assessment     ]
   |                         |<>--{0..*}--[ Method         ]
   |                         |<>--{0..*}--[ Flow           ]
   |                         |<>--{0..*}--[ Expectation    ]
   |                         |<>--{0..1}--[ Record         ]
   |                         |<>--{0..*}--[ EventData      ]
   |                         |<>--{0..*}--[ AdditionalData ]
   +-------------------------+

                      Figure 29: The EventData Class

   The aggregate classes of the EventData class are:

   Description
      Zero or more.  ML_STRING.  A free-form textual description of the
      event.

   DetectTime
      Zero or one.  DATETIME.  The time the event was detected.

   StartTime
      Zero or one.  DATETIME.  The time the event started.

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   EndTime
      Zero or one.  DATETIME.  The time the event ended.

   RecoveryTime
      Zero or one.  DATETIME.  The time the site recovered from the
      event.

   ReportTime
      One.  DATETIME.  The time the event was reported.

   Contact
      Zero or more.  Contact information for the parties involved in the
      event.  See Section 3.9.

   Discovery
      Zero or more.  The means by which the event was detected.  See
      Section 3.10.

   Assessment
      Zero or one.  The impact of the event on the target and the
      actions taken.  See Section 3.12.

   Method
      Zero or more.  The technique used by the intruder in the event.
      See Section 3.11.

   Flow
      Zero or more.  A description of the systems or networks involved.
      See Section 3.16.

   Expectation
      Zero or more.  The expected action to be performed by the
      recipient for the described event.  See Section 3.15.

   Record
      Zero or one.  Supportive data (e.g., log files) that provides
      additional information about the event.  See Section 3.22.

   EventData
      Zero or more.  EventData instances contained within another
      EventData instance inherit the values of the parent(s); this
      recursive definition can be used to group common data pertaining
      to multiple events.  When EventData elements are defined
      recursively, only the leaf instances (those EventData instances
      not containing other EventData instances) represent actual events.
      See Section 3.14.

   AdditionalData

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      Zero or more.  EXTENSION.  An extension mechanism for data not
      explicitly represented in the data model.

   At least one of the aggregate classes MUST be present in an instance
   of the EventData class.  This is not enforced in the IODEF schema as
   there is no simple way to accomplish it.

   The attributes of the EventData class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.  The default value is
      "default".

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.14.1.  Relating the Incident and EventData Classes

   There is substantial overlap in the Incident and EventData classes.
   Nevertheless, the semantics of these classes are quite different.
   The Incident class provides summary information about the entire
   incident, while the EventData class provides information about the
   individual events comprising the incident.  In the most common case,
   the EventData class will provide more specific information for the
   general description provided in the Incident class.  However, it may
   also be possible that the overall summarized information about the
   incident conflicts with some individual information in an EventData
   class when there is a substantial composition of various events in
   the incident.  In such a case, the interpretation of the more
   specific EventData MUST supersede the more generic information
   provided in Incident.

3.14.2.  Cardinality of EventData

   The EventData class is container for the properties of an event in an
   incident.  These properties include: the hosts involved, impact of
   the incident activity on the hosts, forensic logs, etc.  With an
   instance of the EventData class, hosts are grouped around these
   common properties.

   The recursive definition of the EventData class (the EventData class
   is aggregated into the EventData class) provides a way to relate
   information without requiring the explicit use of unique attribute
   identifiers in the classes or duplicating information.  Instead, the

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   relative depth (nesting) of a class is used to group (relate)
   information.

   For example, an EventData class might be used to describe two
   machines involved in an incident.  This description can be achieved
   using multiple instances of the Flow class.  It happens that there is
   a common technical contact (i.e., Contact class) for these two
   machines, but the impact (i.e., Assessment class) on them is
   different.  A depiction of the representation for this situation can
   be found in Figure 30.

   +------------------+
   | EventData        |
   +------------------+
   |                  |<>----[ Contact    ]
   |                  |
   |                  |<>----[ EventData  ]<>----[ Flow     ]
   |                  |      [            ]<>----[ Assessment ]
   |                  |
   |                  |<>----[ EventData  ]<>----[ Flow     ]
   |                  |      [            ]<>----[ Assessment ]
   +------------------+

                Figure 30: Recursion in the EventData Class

3.15.  Expectation Class

   The Expectation class conveys to the recipient of the IODEF document
   the actions the sender is requesting.  The scope of the requested
   action is limited to purview of the EventData class in which this
   class is aggregated.

   +-------------------------+
   | Expectation             |
   +-------------------------+
   | ENUM action             |<>--{0..*}--[ Description ]
   | STRING ext-action       |<>--{0..*}--[ DefinedCOA  ]
   | ENUM severity           |<>--{0..1}--[ StartTime   ]
   | ENUM restriction        |<>--{0..1}--[ EndTime     ]
   | STRING ext-restriction  |<>--{0..1}--[ Contact     ]
   | ID observable-id        |
   +-------------------------+

                     Figure 31: The Expectation Class

   The aggregate classes of the Expectation class are:

   Description

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      Zero or more.  ML_STRING.  A free-form description of the desired
      action(s).

   DefinedCOA
      Zero or more.  ML_STRING.  A unique identifier meaningful to the
      sender and recipient of this document that references a course of
      action.  This class MUST be present if the action attribute is set
      to "defined-coa".

   StartTime
      Zero or one.  DATETIME.  The time at which the sender would like
      the action performed.  A timestamp that is earlier than the
      ReportTime specified in the Incident class denotes that the sender
      would like the action performed as soon as possible.  The absence
      of this element indicates no expectations of when the recipient
      would like the action performed.

   EndTime
      Zero or one.  DATETIME.  The time by which the sender expects the
      recipient to complete the action.  If the recipient cannot
      complete the action before EndTime, the recipient MUST NOT carry
      out the action.  Because of transit delays, clock drift, and so
      on, the sender MUST be prepared for the recipient to have carried
      out the action, even if it completes past EndTime.

   Contact
      Zero or one.  The expected actor for the action.  See Section 3.9.

   The attributes of the Expectation class are:

   action
      Optional.  ENUM.  Classifies the type of action requested.  This
      attribute is an enumerated list with a default value of "other".
      These values are maintained in the "Expectation-action" IANA
      registry per Table 1.

      1.   nothing.  No action is requested.  Do nothing with the
           information.

      2.   contact-source-site.  Contact the site(s) identified as the
           source of the activity.

      3.   contact-target-site.  Contact the site(s) identified as the
           target of the activity.

      4.   contact-sender.  Contact the originator of the document.

      5.   investigate.  Investigate the systems(s) listed in the event.

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      6.   block-host.  Block traffic from the machine(s) listed as
           sources the event.

      7.   block-network.  Block traffic from the network(s) lists as
           sources in the event.

      8.   block-port.  Block the port listed as sources in the event.

      9.   rate-limit-host.  Rate-limit the traffic from the machine(s)
           listed as sources in the event.

      10.  rate-limit-network.  Rate-limit the traffic from the
           network(s) lists as sources in the event.

      11.  rate-limit-port.  Rate-limit the port(s) listed as sources in
           the event.

      12.  redirect-traffic.  Redirect traffic from intended recipient
           for further analysis.

      13.  honeypot.  Redirect traffic to a honeypot for further
           analysis.

      14.  upgrade-software.  Upgrade or patch the software or firmware
           on an asset.

      15.  rebuild-asset.  Reinstall the operating system or
           applications on an asset.

      16.  harden-asset.  Change the configuration an asset (e.g.,
           reduce the number of services or user accounts) to reduce the
           attack surface.

      17.  remediate-other.  Remediate the activity in a way other than
           by rate limiting or blocking.

      18.  status-triage.  Conveys receipts and the triaging of an
           incident.

      19.  status-new-info.  Conveys that new information was received
           for this incident.

      20.  watch-and-report.  Watch for the described activity and share
           if seen.

      21.  training.  Train user to identify or mitigate a threat.

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      22.  defined-coa.  Perform a predefined course of action (COA).
           The COA is named in the DefinedCOA class.

      23.  other.  Perform some custom action described in the
           Description class.

      24.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-action
      Optional.  STRING.  A means by which to extend the action
      attribute.  See Section 5.1.1.

   severity
      Optional.  ENUM.  Indicates the desired priority of the action.
      This attribute is an enumerated list with no default value, and
      the semantics of these relative measures are context dependent.

      1.  low.  Low priority

      2.  medium.  Medium priority

      3.  high.  High priority

   restriction
      Optional.  ENUM.  See Section 3.3.1.  The default value is
      "default".

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.16.  Flow Class

   The Flow class groups related the source and target hosts.

   +------------------+
   | Flow             |
   +------------------+
   |                  |<>--{1..*}--[ System   ]
   +------------------+

                         Figure 32: The Flow Class

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   The aggregate class of the Flow class is:

   System
      One or More.  A host or network involved in an event.  See
      Section 3.17.

   The Flow class has no attributes.

3.17.  System Class

   The System class describes a system or network involved in an event.
   The systems or networks represented by this class are categorized
   according to the role they played in the incident through the
   category attribute.  The value of this category attribute dictates
   the semantics of the aggregated classes in the System class.  If the
   category attribute has a value of "source", then the aggregated
   classes denote the machine and service from which the activity is
   originating.  With a category attribute value of "target" or
   "intermediary", then the machine or service is the one targeted in
   the activity.  A value of "sensor" dictates that this System was part
   of an instrumentation to monitor the network.

   +------------------------+
   | System                 |
   +------------------------+
   | ENUM category          |<>----------[ Node            ]
   | STRING ext-category    |<>--{0..*}--[ NodeRole        ]
   | STRING interface       |<>--{0..*}--[ Service         ]
   | ENUM spoofed           |<>--{0..*}--[ OperatingSystem ]
   | ENUM virtual           |<>--{0..*}--[ Counter         ]
   | ENUM ownership         |<>--{0..*}--[ AssetID         ]
   | STRING ext-ownership   |<>--{0..*}--[ Description     ]
   | ENUM restriction       |<>--{0..*}--[ AdditionalData  ]
   | STRING ext-restriction |
   +------------------------+

                        Figure 33: The System Class

   The aggregate classes of the System class are:

   Node
      One.  A host or network involved in the incident.  See
      Section 3.18.

   NodeRole
      Zero or more.  The intended purpose of the system.  See
      Section 3.18.2.

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   Service
      Zero or more.  A network service running on the system.  See
      Section 3.20.

   OperatingSystem
      Zero or more.  SOFTWARE.  The operating system running on the
      system.

   Counter
      Zero or more.  A counter with which to summarize properties of
      this host or network.  See Section 3.18.3.

   AssetID
      Zero or more.  STRING.  An asset identifier for the System.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      System.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   The attributes of the System class are:

   category
      Optional.  ENUM.  Classifies the role the host or network played
      in the incident.  These values are maintained in the "System-
      category" IANA registry per Table 1.  The possible values are:

      1.  source.  The System was the source of the event.

      2.  target.  The System was the target of the event.

      3.  intermediate.  The System was an intermediary in the event.

      4.  sensor.  The System was a sensor monitoring the event.

      5.  infrastructure.  The System was an infrastructure node of
          IODEF document exchange.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-category
      Optional.  STRING.  A means by which to extend the category
      attribute.  See Section 5.1.1.

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   interface
      Optional.  STRING.  Specifies the interface on which the event(s)
      on this System originated.  If the Node class specifies a network
      rather than a host, this attribute has no meaning.

   spoofed
      Optional.  ENUM.  An indication of confidence in whether this
      System was the true target or attacking host.  The permitted
      values for this attribute are shown below.  The default value is
      "unknown".

      1.  unknown.  The accuracy of the category attribute value is
          unknown.

      2.  yes.  The category attribute value is probably incorrect.  In
          the case of a source, the System is likely a decoy; with a
          target, the System was likely not the intended victim.

      3.  no.  The category attribute value is believed to be correct.

   virtual
      Optional.  ENUM.  Indicates whether this System is a virtual or
      physical device.  The default value is "unknown".  The possible
      values are:

      1.  yes.  The System is a virtual device.

      2.  no.  The System is a physical device.

      3.  unknown.  It is not known if the System is virtual.

   ownership
      Optional.  ENUM.  Describes the ownership of this System relative
      to the sender of the IODEF document.  These values are maintained
      in the "System-ownership" IANA registry per Table 1.  The possible
      values are:

      1.  organization.  The System is owned by the organization.

      2.  personal.  The System is owned by employee or affiliate of the
          organization.

      3.  partner.  The System is owned by a partner of the
          organization.

      4.  customer.  The System is owned by a customer of the
          organization.

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      5.  no-relationship.  The System is owned by an entity that has no
          known relationship with the organization.

      6.  unknown.  The ownership of the System is unknown.

      7.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-ownership
      Optional.  STRING.  A means by which to extend the ownership
      attribute.  See Section 5.1.1.

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.18.  Node Class

   The Node class names an asset or network.

   This class was derived from [RFC4765].

   +---------------+
   | Node          |
   +---------------+
   |               |<>--{0..*}--[ DomainData    ]
   |               |<>--{0..*}--[ Address       ]
   |               |<>--{0..1}--[ PostalAddress ]
   |               |<>--{0..*}--[ Location      ]
   |               |<>--{0..*}--[ Counter       ]
   +---------------+

                         Figure 34: The Node Class

   The aggregate classes of the Node class are:

   DomainData
      Zero or more.  The detailed domain (DNS) information associated
      with this Node.  If an Address is not provided, at least one
      DomainData MUST be specified.  See Section 3.19.

   Address

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      Zero or more.  The hardware, network, or application address of
      the Node.  If a DomainData is not provided, at least one Address
      MUST be specified.  See Section 3.18.1.

   PostalAddress
      Zero or one.  POSTAL.  The postal address of the asset.

   Location
      Zero or more.  ML_STRING.  A free-form description of the physical
      location of the Node.  This description may provide a more
      detailed description of where in the PostalAddress this Node is
      found (e.g., room number, rack number, slot number in a chassis).

   Counter
      Zero or more.  A counter with which to summarizes properties of
      this host or network.  See Section 3.18.3.

   The Node class has no attributes.

3.18.1.  Address Class

   The Address class represents a hardware (layer-2), network (layer-3),
   or application (layer-7) address.

   This class was derived from [RFC4765].

   +-------------------------+
   | Address                 |
   +-------------------------+
   | STRING                  |
   |                         |
   | ENUM category           |
   | STRING ext-category     |
   | STRING vlan-name        |
   | INTEGER vlan-num        |
   | ID observable-id        |
   +-------------------------+

                       Figure 35: The Address Class

   The content of the class is an address of type STRING whose semantics
   are determined by the category attribute.

   The attributes of the Address class are:

   category
      Optional.  ENUM.  The type of address represented.  The permitted
      values for this attribute are shown below.  The default value is

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      "ipv6-addr".  These values are maintained in the "Address-
      category" IANA registry per Table 1.

      1.   asn.  Autonomous System Number

      2.   atm.  Asynchronous Transfer Mode (ATM) address

      3.   e-mail.  Electronic mail address (RFC 822)

      4.   ipv4-addr.  IPv4 host address in dotted-decimal notation
           (a.b.c.d)

      5.   ipv4-net.  IPv4 network address in dotted-decimal notation,
           slash, significant bits (i.e., a.b.c.d/nn)

      6.   ipv4-net-mask.  IPv4 network address in dotted-decimal
           notation, slash, network mask in dotted-decimal notation
           (i.e., a.b.c.d/w.x.y.z)

      7.   ipv6-addr.  IPv6 host address

      8.   ipv6-net.  IPv6 network address, slash, significant bits

      9.   ipv6-net-mask.  IPv6 network address, slash, network mask

      10.  mac.  Media Access Control (MAC) address (i.e., a:b:c:d:e:f)

      11.  site-uri.  A URL or URI for a resource.

      12.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-category
      Optional.  STRING.  A means by which to extend the category
      attribute.  See Section 5.1.1.

   vlan-name
      Optional.  STRING.  The name of the Virtual LAN to which the
      address belongs.

   vlan-num
      Optional.  STRING.  The number of the Virtual LAN to which the
      address belongs.

   observable-id
      Optional.  ID.  See Section 3.3.2.

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3.18.2.  NodeRole Class

   The NodeRole class describes the function performed by a particular
   system.

   +-----------------------+
   | NodeRole              |
   +-----------------------+
   | ENUM category         |<>--{0..*}--[ Description ]
   | STRING ext-category   |
   +-----------------------+

                       Figure 36: The NodeRole Class

   The aggregate class of the NodeRole class is:

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      role of the system.

   The attributes of the NodeRole class are:

   xml:lang
      Optional.  ENUM.  A language identifier per Section 2.12 of
      [W3C.XML] whose values and form are described in [RFC5646].  The
      interpretation of this code is described in Section 6.

   translation-id
      Optional.  STRING.  An identifier to relate other instances of
      this class as translations of this text.  See Section 6.

   category
      Required.  ENUM.  Functionality provided by a node.  These values
      are maintained in the "NodeRole-category" IANA registry per
      Table 1.

      1.   client.  Client computer

      2.   client-enterprise.  Client computer on the enterprise network

      3.   client-partner.  Client computer on network of a partner

      4.   client-remote.  Client computer remotely connected to the
           enterprise network

      5.   client-kiosk.  Client computer is serves as a kiosk

      6.   client-mobile.  Client is a mobile device

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      7.   server-internal.  Server with internal services

      8.   server-public.  Server with public services

      9.   www.  WWW server

      10.  mail.  Mail server

      11.  webmail.  Web mail server

      12.  messaging.  Messaging server (e.g., NNTP, IRC, IM)

      13.  streaming.  Streaming-media server

      14.  voice.  Voice server (e.g., SIP, H.323)

      15.  file.  File server (e.g., SMB, CVS, AFS)

      16.  ftp.  FTP server

      17.  p2p.  Peer-to-peer node

      18.  name.  Name server (e.g., DNS, WINS)

      19.  directory.  Directory server (e.g., LDAP, finger, whois)

      20.  credential.  Credential server (e.g., domain controller,
           Kerberos)

      21.  print.  Print server

      22.  application.  Application server

      23.  database.  Database server

      24.  backup.  Backup server

      25.  dhcp.  DHCP server

      26.  assessment.  Assessment server (e.g., vulnerability scanner,
           end-point assessment)

      27.  source-control.  Source code control server

      28.  config-management.  Configuration management server

      29.  monitoring.  Security monitoring server (e.g., IDS)

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      30.  infra.  Infrastructure server (e.g., router, firewall, DHCP)

      31.  infra-firewall.  Firewall

      32.  infra-router.  Router

      33.  infra-switch.  Switch

      34.  camera.  Camera and video system

      35.  proxy.  Proxy server

      36.  remote-access.  Remote access server

      37.  log.  Log server (e.g., syslog)

      38.  virtualization.  Server running virtual machines

      39.  pos.  Point-of-sale device

      40.  scada.  Supervisory control and data acquisition system

      41.  scada-supervisory.  Supervisory system for a SCADA

      42.  sinkhole.  Traffic sinkhole destination

      43.  honeypot.  Honeypot server

      44.  anonymization.  Anonymization server (e.g., Tor node)

      45.  c2-server.  Malicious command and control server

      46.  malware-distribution.  Server that distributes malware

      47.  drop-server.  Server to which exfiltrated content is
           uploaded.

      48.  hop-point.  Intermediary server used to get to a victim.

      49.  reflector.  A system used in a reflector attacker.

      50.  phishing-site.  Site hosting phishing content

      51.  spear-phishing-site.  Site hosting spear-phishing content

      52.  recruiting-site.  Site to recruit

      53.  fraudulent-site.  Fraudulent site.

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      54.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-category
      Optional.  STRING.  A means by which to extend the category
      attribute.  See Section 5.1.1.

3.18.3.  Counter Class

   The Counter class summarize multiple occurrences of some event, or
   conveys counts or rates on various features (e.g., packets, sessions,
   events).

   The value of the counter is the element content with its units
   represented in the type attribute.  A rate for a given feature can be
   expressed by setting the duration attribute.  The complete semantics
   are entirely context dependent based on the class in which the
   Counter is aggregated.

   +---------------------+
   | Counter             |
   +---------------------+
   | REAL                |
   |                     |
   | ENUM type           |
   | STRING ext-type     |
   | ENUM unit           |
   | STRING ext-unit     |
   | STRING meaning      |
   | ENUM duration       |
   | STRING ext-duration |
   +---------------------+

                       Figure 37: The Counter Class

   The content of the class is a counter value of type REAL.

   The attributes of the Counter class are:

   type
      Required.  ENUM.  Specifies the type of counter specified in the
      element content.  These values are maintained in the "Counter-
      type" IANA registry per Table 1.

      1.  count.  The Counter class value is a counter.

      2.  peak.  The Counter class value is a peak value.

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      3.  average.  The Counter class value is an average.

      4.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

   unit
      Required.  ENUM.  Specifies the units of the element content.
      These values are maintained in the "Counter-unit" IANA registry
      per Table 1.

      1.   byte.  Bytes transferred.

      2.   mbit.  Megabits (Mbits) transfered.

      3.   packet.  Packets.

      4.   flow.  Network flow records.

      5.   session.  Sessions.

      6.   alert.  Notifications generated by another system (e.g., IDS
           or SIM).

      7.   message.  Messages (e.g., mail messages).

      8.   event.  Events.

      9.   host.  Hosts.

      10.  site.  Site.

      11.  organization.  Organizations.

      12.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-unit
      Optional.  STRING.  A means by which to extend the unit attribute.
      See Section 5.1.1.

   meaning

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      Optional.  STRING.  A free-form description of the metric
      represented by the Counter.

   duration
      Optional.  ENUM.  If present, the Counter class represents a rate.
      This attribute specifies unit of time over which the rate whose
      units are specified in the unit attribute is being conveyed.  This
      attribute is the the denominator of the rate (where the unit
      attribute specified the nominator).  The possible values of this
      attribute are defined in Section 3.12.3

   ext-duration
      Optional.  STRING.  A means by which to extend the duration
      attribute.  See Section 5.1.1.

3.19.  DomainData Class

   The DomainData class describes a domain name and meta-data associated
   with this domain.

   +--------------------------+
   | DomainData               |
   +--------------------------+
   | ENUM system-status       |<>----------[ Name                 ]
   | STRING ext-system-status |<>--{0..1}--[ DateDomainWasChecked ]
   | ENUM domain-status       |<>--{0..1}--[ RegistrationDate     ]
   | STRING ext-domain-status |<>--{0..1}--[ ExpirationDate       ]
   | ID observable-id         |<>--{0..*}--[ RelatedDNS           ]
   |                          |<>--{0..*}--[ Nameservers          ]
   |                          |<>--{0..1}--[ DomainContacts       ]
   +--------------------------+

                      Figure 38: The DomainData Class

   The aggregate classes of the DomainData class are:

   Name
      One.  STRING.  The domain name of the Node (e.g., fully qualified
      domain name).

   DateDomainWasChecked
      Zero or one.  DATETIME.  A timestamp of when the Name was
      resolved.

   RegistrationDate
      Zero or one.  DATETIME.  A timestamp of when domain listed in Name
      was registered.

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   ExpirationDate
      Zero or one.  DATETIME.  A timestamp of when the domain listed in
      Name is set to expire.

   RelatedDNS
      Zero or more.  EXTENSION.  Additional DNS records associated with
      this domain.

   Nameservers
      Zero or more.  The name servers identified for the domain listed
      in Name.  See Section 3.19.1.

   DomainContacts
      Zero or one.  Contact information for the domain listed in Name
      supplied by the registrar or through a whois query.

   The attributes of the DomainData class are:

   system-status
      Required.  ENUM.  Assesses the domain's involvement in the event.
      These values are maintained in the "DomainData-system-status" IANA
      registry per Table 1.

      1.  spoofed.  This domain was spoofed.

      2.  fraudulent.  This domain was operated with fraudulent
          intentions.

      3.  innocent-hacked.  This domain was compromised by a third
          party.

      4.  innocent-hijacked.  This domain was deliberately hijacked.

      5.  unknown.  No categorization for this domain known.

      6.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-system-status
      Optional.  STRING.  A means by which to extend the system-status
      attribute.  See Section 5.1.1.

   domain-status
      Required.  ENUM.  Categorizes the registry status of the domain at
      the time the document was generated.  These values and their
      associated descriptions are derived from Section 3.2.2 of

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      [RFC3982].  These values are maintained in the "DomainData-domain-
      status" IANA registry per Table 1.

      1.   reservedDelegation.  The domain is permanently inactive.

      2.   assignedAndActive.  The domain is in a normal state.

      3.   assignedAndInactive.  The domain has an assigned registration
           but the delegation is inactive.

      4.   assignedAndOnHold.  The domain is under dispute.

      5.   revoked.  The domain is in the process of being purged from
           the database.

      6.   transferPending.  The domain is pending a change in
           authority.

      7.   registryLock.  The domain is on hold by the registry.

      8.   registrarLock.  Same as "registryLock".

      9.   other.  The domain has a known status but it is not one of
           the redefined enumerated values.

      10.  unknown.  The domain has an unknown status.

      11.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-domain-status
      Optional.  STRING.  A means by which to extend the domain-status
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.19.1.  Nameservers Class

   The Nameservers class describes the name servers associated with a
   given domain.

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   +--------------------+
   | Nameservers        |
   +--------------------+
   |                    |<>----------[ Server  ]
   |                    |<>--{1..*}--[ Address ]
   +--------------------+

                     Figure 39: The Nameservers Class

   The aggregate classes of the Nameservers class are:

   Server
      One.  STRING.  The domain name of the name server.

   Address
      One or more.  The address of the name server.  The value of the
      category attribute MUST be either "ipv4-addr" or "ipv6-addr".  See
      Section 3.18.1.

   The Nameservers class has no attributes.

3.19.2.  DomainContacts Class

   The DomainContacts class describes the contact information for a
   given domain provided either by the registrar or through a whois
   query.

   This contact information can be explicitly described through a
   Contact class or a reference can be provided to a domain with
   identical contact information.  Either a single SameDomainContact
   MUST be present or one or more Contact classes.

   +--------------------+
   | DomainContacts     |
   +--------------------+
   |                    |<>--{0..1}--[ SameDomainContact ]
   |                    |<>--{1..*}--[ Contact ]
   +--------------------+

                    Figure 40: The DomainContacts Class

   The aggregate classes of the DomainContacts class are:

   SameDomainContact
      Zero or one.  STRING.  A domain name already cited in this
      document or through previous exchange that contains the identical
      contact information as the domain name in question.  The domain

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      contact information associated with this domain should be used
      instead of an explicit definition with the Contact class.

   Contact
      One or more.  Contact information for the domain.  See
      Section 3.9.

   The DomainContacts class has no attributes.

3.20.  Service Class

   The Service class describes a network service of a host or network.
   The service is identified by specific port or list of ports, along
   with the application listening on that port.

   When Service occurs as an aggregate class of a System that is a
   source, then this service is the one from which activity of interest
   is originating.  Conversely, when Service occurs as an aggregate
   class of a System that is a target, then that service is the one to
   which activity of interest is directed.

   This class was derived from [RFC4765].

   +-------------------------+
   | Service                 |
   +-------------------------+
   | INTEGER ip-protocol     |<>--{0..1}--[ ServiceName       ]
   | ID observable-id        |<>--{0..1}--[ Port              ]
   |                         |<>--{0..1}--[ Portlist          ]
   |                         |<>--{0..1}--[ ProtoCode         ]
   |                         |<>--{0..1}--[ ProtoType         ]
   |                         |<>--{0..1}--[ ProtoField        ]
   |                         |<>--{0..1}--[ ApplicationHeader ]
   |                         |<>--{0..1}--[ EmailData         ]
   |                         |<>--{0..1}--[ Application       ]
   +-------------------------+

                       Figure 41: The Service Class

   The aggregate classes of the Service class are:

   ServiceName
      Zero or one.  Identifies the the observed service.

   Port
      Zero or one.  INTEGER.  A port number.

   Portlist

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      Zero or one.  PORTLIST.  A list of port numbers formatted
      according to Section 2.10.

   ProtoCode
      Zero or one.  INTEGER.  A transport layer (layer 4) protocol-
      specific code field (e.g., ICMP code field).

   ProtoType
      Zero or one.  INTEGER.  A transport layer (layer 4) protocol
      specific type field (e.g., ICMP type field).

   ProtoField
      Zero or one.  INTEGER.  A transport layer (layer 4) protocol
      specific flag field (e.g., TCP flag field).

   ApplicationHeader
      Zero or one.  A protocol header.  See Section 3.20.2.

   EmailData
      Zero or one.  Headers associated with an email.  See Section 3.21.

   Application
      Zero or one.  SOFTWARE.  The application bound to the specified
      Port or Portlist.

   Either a Port or Portlist class MUST be specified for a given
   instance of a Service class.

   When a given System classes with category="source" and another with
   category="target" are aggregated into a single Flow class, and each
   of these System classes has a Service and Portlist class, an implicit
   relationship between these Portlists exists.  If N ports are listed
   for a System@category="source", and M ports are listed for
   System@category="target", the number of ports in N must be equal to
   M.  Likewise, the ports MUST be listed in an identical sequence such
   that the n-th port in the source corresponds to the n-th port of the
   target.  If N is greater than 1, a given instance of a Flow class
   MUST only have a single instance of a System@category="source" and
   System@category="target".

   The attributes of the Service class are:

   ip-protocol
      Required.  INTEGER.  The IANA assigned IP protocol number per
      [IANA.Protocols].

   observable-id
      Optional.  ID.  See Section 3.3.2.

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3.20.1.  ServiceName Class

   The ServiceName class names an application protocol.  It can be
   described by referencing an IANA registered protocol, a URL or with
   free-form text.

   +--------------------+
   | ServiceName        |
   +--------------------+
   |                    |<>--{0..1}--[ IANAService       ]
   |                    |<>--{0..*}--[ URL               ]
   |                    |<>--{0..*}--[ Description       ]
   +--------------------+

                     Figure 42: The ServiceName Class

   The aggregate classes of the ServiceName class are:

   IANAService
      Zero or one.  STRING.  The name of the service per the "Service
      Name" field of the [IANA.Ports] registry.

   URL
      Zero or more.  URL.  A URL describing the service.

   Description
      Zero or more.  ML_STRING.  A free-form text description of the
      service.

   At least one of these classes MUST be present.

   The ServiceName class has no attributes.

3.20.2.  ApplicationHeader Class

   The ApplicationHeader class allows the representation of arbitrary
   fields from a protocol header and its corresponding value.

   +--------------------------+
   | ApplicationHeader        |
   +--------------------------+
   |                          |<>--{1..*}--[ ApplicationHeaderField ]
   +--------------------------+

                  Figure 43: The ApplicationHeader Class

   The aggregate class of the ApplicationHeader class is:

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   ApplicationHeaderField
      One or more.  EXTENSION.  A field name and value in the header.
      The 'name' attribute of the ApplicationHeader MUST be set with the
      field name.

   The ApplicationHeader class has no attributes.

3.21.  EmailData Class

   The EmailData class describes headers from an email message.  Common
   headers have dedicated classes, but arbitrary headers can also be
   described.

   +-------------------------+
   | EmailData               |
   +-------------------------+
   | ID observable-id        |<>--{0..1}--[ EmailTo          ]
   |                         |<>--{0..1}--[ EmailFrom        ]
   |                         |<>--{0..1}--[ EmailSubject     ]
   |                         |<>--{0..1}--[ EmailX-Mailer    ]
   |                         |<>--{0..*}--[ EmailHeaderField ]
   |                         |<>--{0..*}--[ HashData         ]
   |                         |<>--{0..*}--[ SignatureData    ]
   +-------------------------+

                        Figure 44: EmailData Class

   The aggregate classes of the EmailData class are:

   EmailTo
      Zero or one.  EMAIL.  The value of the "To:" header field
      (Section 3.6.3 of [RFC5322]) in an email.

   EmailFrom
      Zero or one.  EMAIL.  The value of the "From:" header field
      (Section 3.6.2 of [RFC5322]) in an email.

   EmailSubject
      Zero or one.  STRING.  The value of the "Subject:" header field in
      an email.  See Section 3.6.4 of [RFC5322].

   EmailX-Mailer
      Zero or one.  STRING.  The value of the "X-Mailer:" header field
      in an email.

   EmailHeaderField
      Zero or one.  EXTENSION.  The value of an arbitrary header field
      in the email.  The attribute of EmailHeaderField MUST be set as

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      follows: name MUST be the the name of the SMTP header field; and
      dtype="string".

   HashData
      Zero or One.  Hash(es) associated with this email.  See
      Section 3.26.

   SignatureData
      Zero or One.  Signature(s) associated with this email.  See
      Section 3.27.

   The attribute of the EmailData class is:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.22.  Record Class

   The Record class is a container class for log and audit data that
   provides supportive information about the incident.  The source of
   this data will often be the output of monitoring tools.  These logs
   substantiate the activity described in the document.

   +------------------------+
   | Record                 |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ RecordData ]
   | STRING ext-restriction |
   +------------------------+

                          Figure 45: Record Class

   The aggregate classes of the Record class are:

   RecordData
      One or more.  Log or audit data generated by a particular type of
      sensor.  Separate instances of the RecordData class SHOULD be used
      for each sensor type.  See Section 3.22.1.

   The attributes of the Record class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

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3.22.1.  RecordData Class

   The RecordData class groups log or audit data from a given sensor
   (e.g., IDS, firewall log) and provides a way to annotate the output.

   +------------------------+
   | RecordData             |
   +------------------------+
   | ENUM restriction       |<>--{0..1}--[ DateTime               ]
   | STRING ext-restriction |<>--{0..*}--[ Description            ]
   | ID observable-id       |<>--{0..1}--[ Application            ]
   |                        |<>--{0..*}--[ RecordPattern          ]
   |                        |<>--{0..*}--[ RecordItem             ]
   |                        |<>--{0..*}--[ FileData               ]
   |                        |<>--{0..*}--[ CertificateData        ]
   |                        |<>--{0..*}--
   |                        |       [ WindowsRegistryKeysModified ]
   |                        |<>--{0..*}--[ AdditionalData         ]
   +------------------------+

                      Figure 46: The RecordData Class

   The aggregate classes of the RecordData class are:

   DateTime
      Zero or one.  DATETIME.  Timestamp of the RecordItem data.

   Description
      Zero or more.  ML_STRING.  Free-form textual description of the
      provided RecordItem data.  At minimum, this description should
      convey the significance of the provided RecordItem data.

   Application
      Zero or one.  SOFTWARE.  Information about the sensor used to
      generate the RecordItem data.

   RecordPattern
      Zero or more.  A search string to precisely find the relevant data
      in a RecordItem.  See Section 3.22.2.

   RecordItem
      Zero or more.  EXTENSION.  Log, audit, or forensic data to support
      the conclusions made during the course of analyzing the incident.

   FileData
      Zero or one.  The file name and hash of a file indicator.  See
      Section 3.25.

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   WindowsRegistryKeysModified
      Zero or more.  The registry keys that were modified that are
      indicator(s).  See Section 3.23.

   AdditionalData
      Zero or more.  EXTENSION.  An extension mechanism for data not
      explicitly represented in the data model.

   The attributes of the RecordData class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.22.2.  RecordPattern Class

   The RecordPattern class describes where in the content of the
   RecordItem relevant information can be found.  It provides a way to
   reference subsets of information, identified by a pattern, in a large
   log file, audit trail, or forensic data.

   +-----------------------+
   | RecordPattern         |
   +-----------------------+
   | STRING                |
   |                       |
   | ENUM type             |
   | STRING ext-type       |
   | INTEGER offset        |
   | ENUM offsetunit       |
   | STRING ext-offsetunit |
   | INTEGER instance      |
   +-----------------------+

                    Figure 47: The RecordPattern Class

   The content of the class is the specific pattern to search within the
   RecordItem of type STRING.

   The attributes of the RecordPattern class are:

   type

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      Required.  ENUM.  Describes the type of pattern being specified in
      the element content.  The default is "regex".  These values are
      maintained in the "RecordPattern-type" IANA registry per Table 1.

      1.  regex.  regular expression as defined by POSIX Extended
          Regular Expressions (ERE) in Chapter 9 of [IEEE.POSIX].

      2.  binary.  Binhex encoded binary pattern, per the HEXBIN data
          type.

      3.  xpath.  XML Path (XPath) [W3C.XPATH]

      4.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

   offset
      Optional.  INTEGER.  Amount of units (determined by the offsetunit
      attribute) to seek into the RecordItem data before matching the
      pattern.

   offsetunit
      Optional.  ENUM.  Describes the units of the offset attribute.
      The default is "line".  These values are maintained in the
      "RecordPattern-offsetunit" IANA registry per Table 1.

      1.  line.  Offset is a count of lines.

      2.  byte.  Offset is a count of bytes.

      3.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-offsetunit
      Optional.  STRING.  A means by which to extend the offsetunit
      attribute.  See Section 5.1.1.

   instance
      Optional.  INTEGER.  Number of types to apply the specified
      pattern.

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3.23.  WindowsRegistryKeysModified Class

   The WindowsRegistryKeysModified class describes Windows operating
   system registry keys and the operations that were performed on them.
   This class was derived from [RFC5901].

   +-----------------------------+
   | WindowsRegistryKeysModified |
   +-----------------------------+
   | ID observable-id            |<>--{1..*}--[ Key ]
   +-----------------------------+

             Figure 48: The WindowsRegistryKeysModified Class

   The aggregate classes of the WindowsRegistryKeysModified class are:

   Key
      One or more.  The Window registry key.  See Section 3.23.1.

   The attribute of the WindowsRegistryKeysModified class is:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.23.1.  Key Class

   The Key class describes a particular Windows operating system
   registry key name and value pair, and the operation performed on it.

   +---------------------------+
   | Key                       |
   +---------------------------+
   | ENUM registryaction       |<>----------[ KeyName ]
   | STRING ext-registryaction |<>--{0..1}--[ KeyValue ]
   | ID observable-id          |
   +---------------------------+

                         Figure 49: The Key Class

   The aggregate classes of the Key class are:

   KeyName
      One.  STRING.  The name of the Windows operating system registry
      key (e.g.,[HKEY_LOCAL_MACHINE\Software\Test\KeyName])

   KeyValue
      Zero or one.  STRING.  The value of the associated registry key
      encoded as in Microsoft .reg files [KB310516].

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   The attributes of the Key class are:

   registryaction
      Optional.  ENUM.  The type of action taken on the registry key.
      These values are maintained in the "Key-registryaction" IANA
      registry per Table 1.

      1.  add-key.  Registry key added.

      2.  add-value.  Value added to registry key.

      3.  delete-key.  Registry key deleted.

      4.  delete-value.  Value deleted from registry key.

      5.  modify-key.  Registry key modified.

      6.  modify-value.  Value modified for registry key.

      7.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-registryaction
      Optional.  STRING.  A means by which to extend the registryaction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.24.  CertificateData Class

   The CertificateData class describes X.509 certificates.

   +------------------------+
   | CertificateData        |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ Certificate    ]
   | STRING ext-restriction |
   | ID observable-id       |
   +------------------------+

                   Figure 50: The CertificateData Class

   The aggregate classes of the CertificateData class are:

   Certificate
      One or more.  A certificate.  See Section 3.24.1.

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   The attributes of the CertificateData class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.24.1.  Certificate Class

   The Certificate class describes a given X.509 certificate or
   certificate chain.

   +--------------------------+
   | Certificate              |
   +--------------------------+
   | ID observable-id         |<>----------[ ds: X509Data   ]
   |                          |<>--{0..*}--[ Description    ]
   +--------------------------+

                     Figure 51: The Certificate Class

   The aggregate classes of the Certificate class are:

   ds:X509Data
      One.  A given X.509 certificate or chain.  See Section 4.4.4 of
      [W3C.XMLSIG].

   Description
      Zero or more.  ML_STRING.  Free-form textual description
      explaining the context of this certificate.

   The attributes of the Certificate class are:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.25.  FileData Class

   The FileData class describes files of interest identified during the
   analysis of an incident.

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   +------------------------+
   | FileData               |
   +------------------------+
   | ENUM restriction       |<>--{1..*}--[ File      ]
   | STRING ext-restriction |
   | ID observable-id       |
   +------------------------+

                       Figure 52: The FileData Class

   The aggregate classes of the FileData class are:

   File
      One or more.  A description of a file.  See Section 3.25.1.

   The attributes of the FileData class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.25.1.  File Class

   The File class describes a file and its associated meta data.

   +-----------------------+
   | File                  |
   +-----------------------+
   | ID observable-id      |<>--{0..1}--[ FileName           ]
   |                       |<>--{0..1}--[ FileSize           ]
   |                       |<>--{0..1}--[ FileType           ]
   |                       |<>--{0..*}--[ URL                ]
   |                       |<>--{0..1}--[ HashData           ]
   |                       |<>--{0..1}--[ SignatureData      ]
   |                       |<>--{0..1}--[ AssociatedSoftware ]
   |                       |<>--{0..*}--[ FileProperties     ]
   +-----------------------+

                         Figure 53: The File Class

   The aggregate classes of the File class are:

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   FileName
      Zero or One.  STRING.  The name of the file.

   FileSize
      Zero or One.  INTEGER.  The size of the file in bytes.

   FileType
      Zero or One.  STRING.  The type of file per the IANA Media Types
      Registry [IANA.Media].  Valid values correspond to the text in the
      "Template" column (e.g., "application/pdf").

   URL
      Zero or more.  URL.  A URL reference to the file.

   HashData
      Zero or One.  Hash(es) associated with this file.  See
      Section 3.26.

   SignatureData
      Zero or One.  Signature(s) associated with this file.  See
      Section 3.27.

   AssociatedSoftware
      Zero or One.  SOFTWARE.  The software application or operating
      system to which this file belongs.

   FileProperties
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model to describe properties of the file.

   The attributes of the File class are:

   observable-id
      Optional.  ID.  See Section 3.3.2.

3.26.  HashData Class

   The HashData class describes different types of hashes on an given
   object (e.g., file, part of a file, email).

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   +--------------------------+
   | HashData                 |
   +--------------------------+
   | ENUM scope               |<>--{0..1}--[ HashTarget   ]
   |                          |<>--{0..*}--[ Hash         ]
   |                          |<>--{0..*}--[ FuzzyHash    ]
   +--------------------------+

                       Figure 54: The HashData Class

   The aggregate classes of the HashData class are:

   HashTarget
      Zero or One.  ML_STRING.  An identifier that references a subset
      of the object per the @scope attribute.

   Hash
      Zero or more.  The hash generated on the object.  See
      Section 3.26.1.

   FuzzyHash
      Zero or more.  The fuzzy hash of the object.  See Section 3.26.2.

   A single instance of Hash or FuzzyHash MUST be present.

   The attribute of the HashData class is:

   scope
      Required.  ENUM.  Describes the scope of the hash on a type of
      object.  These values are maintained in the "HashData-scope" IANA
      registry per Table 1.

      1.  file-contents.  A hash computed over the entire contents of a
          file.

      2.  file-pe-section.  A hash computed on a given section of a
          Windows Portable Executable (PE) file.  If set to this value,
          the HashTargetId class MUST identify the section being hashed.
          This section is identified by an ordinal number (starting at
          1) corresponding to the the order in which the given section
          header was defined in the Section Table of the PE file header.

      3.  file-pe-iat.  A hash computed on the Import Address
          Table (IAT) of a PE file.  As IAT hashes are often tool
          dependent, if this value is set, the HashTargetId class MUST
          specify the tool used to generate the hash.

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      4.  file-pe-resource.  A hash computed on a given resource in a PE
          file.  If set to this value, the HashTargetId class MUST
          identify the resource being hashed.  This resource is
          identified by an ordinal number (starting at 1) corresponding
          to the oder in which the given resource is declared in the
          Resource Directory of the Data Dictionary in the PE file
          header.

      5.  file-pdf-object.  A hash computed on a given object in a
          Portable Document Format (PDF) file.  If set to this value,
          the HashTargetId class MUST identify the object being hashed.
          This object is identified by its offset in the PDF file.

      6.  email-hash.  A hash computed over the headers and body of an
          email message.

      7.  email-headers-hash.  A hash computed over all of the headers
          of an email message.

      8.  email-body-hash.  A hash computed over the body of an email
          message.

      9.  ext-value.  A value used to indicate that this attribute is
          extended and the actual value is provided using the
          corresponding ext-* attribute.  See Section 5.1.1.

   ext-scope
      Optional.  STRING.  A means by which to extend the scope
      attribute.  See Section 5.1.1.

3.26.1.  Hash Class

   The Hash class describes a specific hash value, algorithm, and an
   application used to generate it.

   +----------------+
   | Hash           |
   +----------------+
   |                |<>----------[ ds:DigestMethod            ]
   |                |<>----------[ ds:DigestValue             ]
   |                |<>--{0..1}--[ ds:CannonicalizationMethod ]
   |                |<>--{0..1}--[ Application                ]
   +----------------+

                         Figure 55: The Hash Class

   The aggregate classes of the Hash class are:

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   ds:DigestMethod
      One.  The hash algorithm used to generate the hash.  See
      Section 4.3.3.5 of [W3C.XMLSIG]

   ds:DigestValue
      One.  The computed hash value.  See Section 4.3.3.6 of
      [W3C.XMLSIG].

   ds:CannonicalizationMethod
      Zero or one.  The canonicalization method used for the has.  See
      Section 4.3.1 of [W3C.XMLSIG].

   Application
      Zero or One.  SOFTWARE.  The application used to calculate the
      hash.

   The HashData class has no attributes.

3.26.2.  FuzzyHash Class

   The FuzzyHash class describes a fuzzy hash (in an extensible way) and
   the application used to generate it.

   +--------------------------+
   | FuzzyHash                |
   +--------------------------+
   |                          |<>--{0..*}--[ AdditionalData ]
   |                          |<>--{0..1}--[ Application    ]
   +--------------------------+

                      Figure 56: The FuzzyHash Class

   The aggregate classes of the FuzzyHash class are:

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   Application
      Zero or One. SOFTWARE.  The application used to calculate the
      hash.

   The FuzzyData class has no attributes.

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3.27.  SignatureData Class

   The SignatureData class describes different signatures on an given
   object.

   +--------------------------+
   | SignatureData            |
   +--------------------------+
   |                          |<>--{1..*}--[ ds:Signature ]
   +--------------------------+

                    Figure 57: The SignatureData Class

   The aggregate class of the SignatureData class is:

   Signature
      One or more.  An given signature.  See Section 4.2 of [W3C.XMLSIG]

   The SignatureData class has no attributes.

3.28.  IndicatorData Class

   The IndicatorData class describes the indicators identified from
   analysis of an incident.

   +--------------------------+
   | IndicatorData            |
   +--------------------------+
   |                          |<>--{1..*}--[ Indicator      ]
   +--------------------------+

                    Figure 58: The IndicatorData Class

   The aggregate class of the IndicatorData class is:

   Indicator
      One or more.  An indicator from the incident.  See Section 3.29.

   The IndicatorData class has no attributes.

3.29.  Indicator Class

   The Indicator class describes a cyber indicator.  An indicator
   consists of observable features and phenomenon that aid in the
   forensic or proactive detection of malicious activity, and associated
   meta-data.  This indicator can be described outright or reference
   observable features and phenomenon described elsewhere in the

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   incident information.  Portions of an incident description can be
   composed to define an indicator, as can the indicators themselves.

   +------------------------+
   | Indicator              |
   +------------------------+
   | ENUM restriction       |<>----------[ IndicatorID            ]
   | STRING ext-restriction |<>--{0..1}--[ AlternativeIndicatorID ]
   |                        |<>--{0..*}--[ Description            ]
   |                        |<>--{0..1}--[ StartTime              ]
   |                        |<>--{0..1}--[ EndTime                ]
   |                        |<>--{0..1}--[ Confidence             ]
   |                        |<>--{0..*}--[ Contact                ]
   |                        |<>--{0..1}--[ Observable             ]
   |                        |<>--{0..1}--[ ObservableReference    ]
   |                        |<>--{0..1}--[ IndicatorExpression    ]
   |                        |<>--{0..1}--[ IndicatorReference     ]
   |                        |<>--{0..*}--[ NodeRole               ]
   |                        |<>--{0..*}--[ AttackPhase            ]
   |                        |<>--{0..*}--[ AdditionalData         ]
   +------------------------+

                      Figure 59: The Indicator Class

   The aggregate classes of the Indicator class are:

   IndicatorID
      One.  An identifier for this indicator.  See Section 3.29.1

   AlternativeIndicatorID
      Zero or one.  An alternative identifier for this indicator.  See
      Section 3.29.2

   Description
      Zero or more.  ML_STRING.  A free-form textual description of the
      indicator.

   StartTime
      Zero or one.  DATETIME.  A timestamp of the start of the time
      period during which this indicator is valid.

   EndTime
      Zero or one.  DATETIME.  A timestamp of the end of the time period
      during which this indicator is valid.

   Confidence
      Zero or one.  An estimate of the confidence in the quality of the
      indicator.  See Section 3.12.5.

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   Contact
      Zero or more.  Contact information for this indicator.  See
      Section 3.9.

   Observable
      Zero or one.  An observable feature or phenomenon of this
      indicator.  See Section 3.29.3.

   ObservableReference
      Zero or one.  A reference to a feature or phenomenon defined
      elsewhere in the document.  See Section 3.29.6.

   IndicatorExpression
      Zero or one.  A composition of observables.  See Section 3.29.4.

   IndicatorReference
      Zero or one.  A reference to an indicator.  See Section 3.29.7.

   NodeRole
      Zero or many.  An indication of the role a system to which this
      indicator is matched might play in an attack.  See Section 3.18.2.

   AttackPhase
      Zero or many.  An indication of which phase in an attack lifecycle
      this indicator might be seen.  See Section 3.29.8.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The Indicator class MUST have exactly one instance of an Observable,
   IndicatorExpression, ObservableReference, or IndicatorReference
   class.

   The StartTime and EndTime classes can be used to define an interval
   during which the indicator is valid.  If both classes are present,
   the indicator is consider valid only during the described interval.
   If neither class is provided, the indicator is considered valid
   during any time interval.  If only a StartTime is provided, the
   indicator is valid anytime after this timestamp.  If only an EndTime
   is provided, the indicator is valid anytime prior to this timestamp.

   The attributes of the Indicator class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction

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      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.29.1.  IndicatorID Class

   The IndicatorID class identifies an indicator with a globally unique
   identifier.  The combination of the name and version attributes, and
   the element content form this identifier.  Indicators generated by
   given CSIRT MUST NOT reuse the same value unless they are referencing
   the same indicator.

   +------------------+
   | IndicatorID      |
   +------------------+
   | ID               |
   |                  |
   | STRING name      |
   | STRING version   |
   +------------------+

                     Figure 60: The IndicatorID Class

   The content of the class is identifier for an indicator of type ID.

   The attributes of the IndicatorID class are:

   name
      Required.  STRING.  An identifier describing the CSIRT that
      created the indicator.  In order to have a globally unique CSIRT
      name, the fully qualified domain name associated with the CSIRT
      MUST be used.  This format is identical to the IncidentID@name
      attribute in Section 3.4.

   version
      Required.  STRING.  A version number of an indicator.

3.29.2.  AlternativeIndicatorID Class

   The AlternativeIndicatorID class lists alternative identifiers for an
   indicator.

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   +-------------------------+
   | AlternativeIndicatorID  |
   +-------------------------+
   | ENUM restriction        |<>--{1..*}--[ IndicatorReference ]
   | STRING ext-restriction  |
   +-------------------------+

                Figure 61: The AlternativeIndicatorID Class

   The aggregate class of the AlternativeIndicatorID class is:

   IndicatorReference
      One or more.  A reference to an indicator.  See Section 3.29.7

   The attributes of the AlternativeIndicatorID class are:

   restriction
      Optional.  ENUM.  See Section 3.3.1.

   ext-restriction
      Optional.  STRING.  A means by which to extend the restriction
      attribute.  See Section 5.1.1.

3.29.3.  Observable Class

   The Observable class describes a feature and phenomenon that can be
   observed or measured for the purposes of detecting malicious
   behavior.

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   +-------------------+
   | Observable        |
   +-------------------+
   |                   |<>--{0..1}--[ Address                     ]
   |                   |<>--{0..1}--[ DomainData                  ]
   |                   |<>--{0..1}--[ Service                     ]
   |                   |<>--{0..1}--[ EmailData                   ]
   |                   |<>--{0..1}--[ Service                     ]
   |                   |<>--{0..1}--[ WindowsRegistryKeysModified ]
   |                   |<>--{0..1}--[ FileData                    ]
   |                   |<>--{0..1}--[ CertificateData             ]
   |                   |<>--{0..1]--[ RegistryHandle              ]
   |                   |<>--{0..1}--[ RecordData                  ]
   |                   |<>--{0..1}--[ EventData                   ]
   |                   |<>--{0..1}--[ Incident                    ]
   |                   |<>--{0..*}--[ Expectation                 ]
   |                   |<>--{0..*}--[ Reference                   ]
   |                   |<>--{0..1}--[ Assessment                  ]
   |                   |<>--{0..1}--[ HistoryItem                 ]
   |                   |<>--{0..1}--[ BulkObservable              ]
   |                   |<>--{0..*}--[ AdditionalData              ]
   +-------------------+

                      Figure 62: The Observable Class

   The aggregate classes of the Observable class are:

   Address
      Zero or One.  An Address observable.  See Section 3.18.1.

   DomainData
      Zero or One.  A DomainData observable.  See Section 3.19.

   Service
      Zero or One.  A Service observable.  See Section 3.20.

   EmailData
      Zero or One.  A EmailData observable.  See Section 3.21.

   WindowsRegistryKeysModified
      Zero or One.  A WindowsRegistryKeysModified observable.  See
      Section 3.23.

   FileData
      Zero or One.  A FileData observable.  See Section 3.25.

   CertificateData
      Zero or One.  A CertificateData observable.  See Section 3.24.

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   RegistryHandle
      Zero or One.  A RegistryHandle observable.  See Section 3.9.1.

   RecordData
      Zero or One.  A RecordData observable.  See Section 3.22.1.

   EventData
      Zero or One.  An EventData observable.  See Section 3.14.

   Incident
      Zero or One.  An Incident observable.  See Section 3.2.

   EventData
      Zero or One.  An EventData observable.  See Section 3.14.

   Expectation
      Zero or One.  An Expectation observable.  See Section 3.15.

   Reference
      Zero or One.  A Reference observable.  See Section 3.11.1.

   Assessment
      Zero or One.  An Assessment observable.  See Section 3.12.

   HistoryItem
      Zero or One.  A HistoryItem observable.  See Section 3.13.1.

   BulkObservable
      Zero or One.  A bulk list of observables.  See Section 3.29.3.1.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The Observable class MUST have exactly one of the possible child
   classes.

   The Observable class has no attributes.

3.29.3.1.  BulkObservable Class

   The BulkObservable class allows the bulk enumeration of single type
   of observables without requiring each one to be encoded individually
   in multiple instances of the same class.  The type attribute
   describes the type observable listed in the child BulkObservableList
   class.  The BulkObservableFormat class optionally provides additional
   meta-data.

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   +---------------------------+
   | BulkObservable            |
   +---------------------------+
   | ENUM type                 |<>--{0..1}--[ BulkObservableFormat ]
   | STRING ext-type           |<>----------[ BulkObservableList   ]
   |                           |<>--{0..*}--[ AdditionalData       ]
   +---------------------------+

                    Figure 63: The BulkObservable Class

   The aggregate classes of the BulkObserable class are:

   BulkObservableFormat
      Zero or one.  Provides additional meta-data about the observables
      enumerated in the BulkObservableList class.  See
      Section 3.29.3.1.1.

   BulkObservableList
      One.  STRING.  A list of observables, one per line.  Each line is
      separated with either a LF character or CR-and-LF characters.  The
      type attribute will specify the which observables will be listed.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The attributes of the BulkObservable class are:

   type
      Optional.  ENUM.  The type of the observable listed in the child
      ObservableList class.  These values are maintained in the
      "BulkObservable-type" IANA registry per Table 1.

      1.   asn.  Autonomous System Number (per the Address@category
           attribute).

      2.   atm.  Asynchronous Transfer Mode (ATM) address (per the
           Address@category attribute).

      3.   e-mail.  Electronic mail address (RFC 822) (per the
           Address@category attribute).

      4.   ipv4-addr.  IPv4 host address in dotted-decimal notation
           (e.g., 192.0.2.1) (per the Address@category attribute).

      5.   ipv4-net.  IPv4 network address in dotted-decimal notation,
           slash, significant bits (e.g., 192.0.2.0/24) (per the
           Address@category attribute).

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      6.   ipv4-net-mask.  IPv4 network address in dotted-decimal
           notation, slash, network mask in dotted-decimal notation
           (i.e., 192.0.2.0/255.255.255.0) (per the Address@category
           attribute).

      7.   ipv6-addr.  IPv6 host address (e.g., 2001:DB8::3) (per the
           Address@category attribute).

      8.   ipv6-net.  IPv6 network address, slash, significant bits
           (e.g., 2001:DB8::/32) (per the Address@category attribute).

      9.   ipv6-net-mask.  IPv6 network address, slash, network mask
           (per the Address@category attribute).

      10.  mac.  Media Access Control (MAC) address (i.e., a:b:c:d:e:f)
           (per the Address@category attribute).

      11.  site-uri.  A URL or URI for a resource (per the
           Address@category attribute).

      12.  fqdn.  Fully qualified domain name.

      13.  domain-name.  A fully qualified domain name or part of a
           name. (e.g., fqdn.example.com, example.com).

      14.  domain-to-ipv4.  A fqdn-to-IPv4 address mapping specified as
           a comma separated list (e.g., "fqdn.example.com, 192.0.2.1").

      15.  domain-to-ipv6.  A fqdn-to-IPv6 address mapping specified as
           a comma separated list (e.g., "fqdn.example.com,
           2001:DB8::3").

      16.  domain-to-ipv4-timestamp.  Same as domain-to-ipv4 but with a
           timestamp (in the DATETIME format) of the resolution (e.g.,
           "fqdn.example.com, 192.0.2.1, 2015-06-11T00:38:31-06:00").

      17.  domain-to-ipv6-timestamp.  Same as domain-to-ipv6 but with a
           timestamp (in the DATETIME format) of the resolution (e.g.,
           "fqdn.example.com, 2001:DB8::3, 2015-06-11T00:38:31-06:00").

      18.  ipv4-port.  An IPv4 address, port and protocol tuple (e.g.,
           192.0.2.1, 80, tcp).  The protocol name corresponds to the
           "Keyword" column in the [IANA.Protocols] registry.

      19.  ipv6-port.  An IPv6 address, port and protocol tuple (e.g.,
           2001:DB8::3, 80, tcp).  The protocol name corresponds to the
           "Keyword" column in the [IANA.Protocols] registry.

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      20.  windows-reg-key.  A Microsoft Windows Registry key.

      21.  file-hash.  A file hash.  The format of this hash is
           described in the Hash class that MUST be present in a sibling
           BulkObservableFormat class.

      22.  email-x-mailer.  An X-Mailer field from an email.

      23.  email-subject.  An email subject line.

      24.  http-user-agent.  A User Agent field from an HTTP request
           header (e.g., "Mozilla/5.0 (Windows NT 6.3; WOW64; rv:38.0)
           Gecko/20100101 Firefox/38.0").

      25.  http-request-uri.  The Request URI from an HTTP request
           header.

      26.  mutex.  The name of a system mutex.

      27.  file-path.  A file path (e.g., "/tmp/local/file",
           "c:\windows\system32\file.sys")

      28.  user-name.  A username.

      29.  ext-value.  A value used to indicate that this attribute is
           extended and the actual value is provided using the
           corresponding ext-* attribute.  See Section 5.1.1.

   ext-type
      Optional.  STRING.  A means by which to extend the type attribute.
      See Section 5.1.1.

3.29.3.1.1.  BulkObservableFormat Class

   The ObservableFormat class specifies meta-data about the format of an
   observable enumerated in a sibling BulkObservableList class.

   +---------------------------+
   | BulkObservableFormat      |
   +---------------------------+
   |                           |<>--{0..1}--[ Hash             ]
   |                           |<>--{0..*}--[ AdditionalData   ]
   +---------------------------+

                 Figure 64: The BulkObservableFormat Class

   The aggregate classes of the BulkObservableFormat class are:

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   Hash
      Zero or one.  Describes the format of a hash.  See Section 3.26.1.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The BulkObservableFormat class has no attributes.

   Either Hash or AdditionalData MUST be present.

3.29.4.  IndicatorExpression Class

   The IndicatorExpression describes an expression composed of observed
   phenomenon or features, or indicators.  Elements of the expression
   can be described directly, reference relevant data from other parts
   of a given IODEF document, or reference previously defined
   indicators.

   All child classes of a given instance of IndicatorExpression form a
   boolean algebraic expression where the operator between them is
   determined by the operator attribute.

   +--------------------------+
   | IndicatorExpression      |
   +--------------------------+
   | ENUM operator            |<>--{0..*}--[ IndicatorExpression  ]
   |                          |<>--{0..*}--[ Observable           ]
   |                          |<>--{0..*}--[ ObservableReference  ]
   |                          |<>--{0..*}--[ IndicatorReference   ]
   |                          |<>--{0..*}--[ AdditionalData       ]
   +--------------------------+

                 Figure 65: The IndicatorExpression Class

   The aggregate classes of the IndicatorExpression class are:

   IndicatorExpression
      Zero or more.  An expression composed of other observables or
      indicators.  See Section 3.29.4.

   Observable
      Zero or more.  A description of an observable.  See
      Section 3.29.3.

   ObservableReference
      Zero or more.  A reference to another observable.  See
      Section 3.29.6.

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   IndicatorReference
      Zero or more.  A reference to another indicator.  See
      Section 3.29.7.

   AdditionalData
      Zero or more.  EXTENSION.  Mechanism by which to extend the data
      model.

   The attribute of the IndicatorExpression class is:

   operator
      Optional.  ENUM.  The operator to be applied between the child
      elements.  The default value is "and".  These values are
      maintained in the "IndicatorExpression-operator" IANA registry per
      Table 1.

      1.  not.  negation operator.

      2.  and.  conjunction operator.

      3.  or.  disjunction operator.

      4.  xor.  exclusive disjunction operator.

3.29.5.  Expressions with IndicatorExpression

   Boolean algebraic expressions can be used specify relationships
   between observables and indicator.  These expressions are constructed
   through the use of the operator attribute and parent-child
   relationships in IndicatorExpressions.  These expressions should be
   parsed as follows:

   1.  The operator specified by the operator attribute is applied
       between each of the child elements of the immediate parent
       IndicatorExpression element.  If no operator attribute is
       specified, it should be assumed to be an AND.

   2.  A nested IndicatorExpression element with a parent
       IndicatorExpression is the equivalent of a parentheses in the
       expression.

   The following four examples illustrate these parsing rules:

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   1     : <IndicatorExpression>
   2 [O1]:    <Observable>..</Observable>
   3 [O2]:    <Observable>..</Observable>
   4     : </IndicatorExpression>

   Equivalent expression: (O1 AND O2)

      Figure 66: Nested elements in an IndicatorExpression without an
                       operator attribute specified

   1     : <IndicatorExpression operator="or">
   2 [O1]:    <Observable>..</Observable>
   3 [O2]:    <Observable>..</Observable>
   4     : </IndicatorExpression>

   Equivalent expression: (O1 OR O2)

   Figure 67: Nested elements in an IndicatorExpression with an operator
                            attribute specified

   1     : <IndicatorExpression operator="or">
   2     :    <IndicatorExpression operator="or">
   2 [O1]:      <Observable>..</Observable>
   3 [O2]:      <Observable>..</Observable>
   4     :    </IndicatorExpression>
   2 [O3]:    <Observable>..</Observable>
   4     : </IndicatorExpression>

   Equivalent expression: ((O1 OR O2) OR O3)

   Figure 68: Nested elements with a recursive IndicatorExpression with
                      an operator attribute specified

   1     : <IndicatorExpression operator="not">
   2     :    <IndicatorExpression operator="and">
   2 [O1]:      <Observable>..</Observable>
   3 [O2]:      <Observable>..</Observable>
   4     :    </IndicatorExpression>
   4     : </IndicatorExpression>

   Equivalent expression: (NOT (O1 AND O2))

   Figure 69: A recursive IndicatorExpression with an operator attribute
                                 specified

   Invalid algebraic expressions while valid XML, MUST not be specified.

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3.29.6.  ObservableReference Class

   The ObservableReference describes a reference to an observable
   feature or phenomenon described elsewhere in the document.

   This class has no content.

   +-------------------------+
   | ObservableReference     |
   +-------------------------+
   | EMPTY                   |
   |                         |
   | IDREF uid-ref           |
   +-------------------------+

                 Figure 70: The ObservableReference Class

   The ObservableReference class has no content.

   The attribute of the ObservableReference class is:

   uid-ref
      Required.  IDREF.  An identifier that serves as a reference to a
      class in the IODEF document.  The referenced class will have this
      identifier set in the observable-id attribute.

3.29.7.  IndicatorReference Class

   The IndicatorReference describes a reference to an indicator.  This
   reference may be to an indicator described in the IODEF document or
   in a previously exchanged IODEF document.

   +--------------------------+
   | IndicatorReference       |
   +--------------------------+
   | EMPTY                    |
   |                          |
   | IDREF uid-ref            |
   | STRING euid-ref          |
   | STRING version           |
   +--------------------------+

                  Figure 71: The IndicatorReference Class

   The IndicatorReference class has no content.

   The attributes of the IndicatorReference class are:

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   uid-ref
      Optional.  IDREF.  An identifier that serves as a reference to an
      Indicator class in the IODEF document.  The referenced Indicator
      class will have this identifier set in the IndicatorID class.

   euid-ref
      Optional.  STRING.  An identifier that references an IndicatorID
      not in this IODEF document.

   version
      Optional.  STRING.  A version number of an indicator.

   Either the uid-ref or the euid-ref attribute MUST be set.

3.29.8.  AttackPhase Class

   The AttackPhase class describes which particular phase of an attack

   +------------------------+
   | AttackPhase            |
   +------------------------+
   |                        |<>--{0..*}--[ AttackPhaseID  ]
   |                        |<>--{0..*}--[ URL            ]
   |                        |<>--{0..*}--[ Description    ]
   |                        |<>--{0..*}--[ AdditionalData ]
   +------------------------+

                       Figure 72: AttackPhase Class

   The aggregate classes of the AttackPhase class are:

   AttackPhaseID
      Zero or more.  STRING.  An identifier for the phase of the attack.

   URL
      Zero or more.  URL.  A URL associated with this phase of the
      attack.

   Description
      Zero or more.  ML_STRING.  A description of the phase of the
      attack.

   AdditionalData
      Zero or more.  EXTENSION.  A mechanism by which to extend the data
      model.

   AttackPhase MUST have at least one instance of a child class.

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   The AttackPhase class has no attributes.

4.  Processing Considerations

   This section defines additional requirements on creating and parsing
   IODEF documents.

4.1.  Encoding

   Every IODEF document MUST begin with an XML declaration, and MUST
   specify the XML version used.  The character encoding MUST also be
   explicitly specified.  UTF-8 [RFC3629] SHOULD be used unless UTF-16
   [RFC2781] is necessary.  Encodings other than UTF-8 and UTF-16 SHOULD
   NOT be used.  The IODEF conforms to all XML data encoding conventions
   and constraints.

   The XML declaration with no character encoding will read as follows:

   <?xml version="1.0" ?>

   When a character encoding is specified, the XML declaration will read
   like the following:

   <?xml version="1.0" encoding="charset" ?>

   Where "charset" is the name of the character encoding as registered
   with the Internet Assigned Numbers Authority (IANA), see [RFC2978].

   The following characters have special meaning in XML and MUST be
   escaped with their entity reference equivalent: "&", "<", ">", "\""
   (double quotation mark), and "'" (apostrophe).  These entity
   references are "&amp;", "&lt;", "&gt;", "&quot;", and "&apos;"
   respectively.

4.2.  IODEF Namespace

   The IODEF schema declares a namespace of
   "urn:ietf:params:xml:ns:iodef-2.0" and registers it per [W3C.XMLNS].
   Each IODEF document MUST include a valid reference to the IODEF
   schema using the "xsi:schemaLocation" attribute.  An example of such
   a declaration would look as follows:

   <IODEF-Document
      version="2.00" lang="en-US"
      xmlns:iodef="urn:ietf:params:xml:ns:iodef-2.0"
      xsi:schemaLocation="urn:ietf:params:xmls:schema:iodef-2.0"

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4.3.  Validation

   The IODEF documents MUST be well-formed XML.  It is RECOMMENDED that
   recipients validate the document against the schema described in
   Section 8.  However, mere conformance to the schema is not sufficient
   for a semantically valid IODEF document.  The text of Section 3
   further describes formatting and constraints; some that cannot be
   readily encoded in the schema.  These MUST must also be considered by
   an IODEF parser.  Furthermore, the enumerated values present in this
   document are a static list that will be incomplete over time as
   select attributes can be extended by a corresponded IANA registry.
   See Table 1.  Hence, the schema to validate a given document MUST be
   dynamically generated from these registry values.

4.4.  Incompatibilities with v1

   Version 2 of the IODEF data model makes a number of changes to
   [RFC5070].  Largely, these changes were additive in nature -- classes
   and enumerated values were added.  The following is a list of
   incompatibilities where the data model has changed between versions:

   o  The IODEF-Document@version attribute is set to "2.0".

   o  The Service@ip_protocol attribute was renamed to @ip-protocol.

   o  The Node/NodeName class was removed in favor of representing
      domain names with Node/DomainData/Name class.  The Node/DataTime
      class was also removed so that the Node/DomainData/
      DateDomainWasChecked class can represent the time at which the
      name to address resolution occurred.

   o  The Node/NodeRole class was moved to System/NodeRole.

   o  The Reference class is now defined by [RFC-ENUM].

   o  Attributes with enumerated values can now also be extended with
      IANA registries.

   o  The data previously represented in the Impact class is now in the
      SystemImpact and IncidentCategory classes.  The Impact class has
      been removed.

   o  The Description class has been redefined to use xml:lang and
      @translation-id.  IODEF-document also uses xml:lang.

   o  The semantics of Counter@type in v1 are now represented in
      Counter@unit.

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   o  The IODEF-Document@formatid attribute has been renamed to @format-
      id.

   o  Incident/ReportTime is no longer mandatory but GenerationTime is.

   o  All derived iodef:MLStringType classes use xml:lang/

   o  The Contact/Fax class is now represented by a generic Contact/
      Telephone class.

   o  The Contact/Telephone, Email and PostalAddress classes were
      redefined from improved internationalization.

5.  Extending the IODEF

   In order to support the changing activity of CSIRTS, the IODEF data
   model will need to evolve along with them.  This section discusses
   how new data elements that have no current representation in the data
   model can be incorporated into the IODEF.  These techniques are
   designed so that adding new data will not require a change to the
   base IODEF schema.  With proven value, well documented extensions can
   be incorporated into future versions of the specification.  However,
   this approach also supports private extensions relevant only to a
   closed consortium.

5.1.  Extending the Enumerated Values of Attributes

   Enumerated values of select attributes can be extended for private
   use through specially marked attributes with the "ext-" prefix.
   Likewise, each extensible attribute has a corresponding IANA registry
   to which to added public extensions.

5.1.1.  Private Extension of Enumerated Values

   The data model supports a means by which to add new enumerated values
   to an attribute without public registration.  For each attribute that
   supports this extension technique, there is a corresponding attribute
   in the same element whose name is identical but with a prefix of
   "ext-".  This special attribute is referred to as the extension
   attribute, and the attribute being extended is referred to as an
   extensible attribute.  For example, an extensible attribute named
   "foo" will have a corresponding extension attribute named "ext-foo".
   An element may have many extensible, and therefore many extension,
   attributes.

   In addition to a corresponding extension attribute, each extensible
   attribute has "ext-value" as one its possible enumerated values.
   This particular value serves as an escape sequence to the implementor

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   to signal that the extension attribute value should be read.
   Otherwise, this value and has no valid meaning.

   In order to add a new enumerated value to an extensible attribute,
   the value of this attribute MUST be set to "ext-value", and the new
   desired value MUST be set in the corresponding extension attribute.
   For example, an extended instance of the type attribute of the
   SystemImpact class would look as follows:

    <SystemImpact type="ext-value" ext-type="new-attack-type">

   A given extension attribute MUST NOT be set unless the corresponding
   extensible attribute has been set to "ext-value".

5.1.2.  Public Extension of Enumerated Values

   Select enumerated value of the attributes defined in the data model
   can be extended by adding entries to the corresponding IANA registry.
   Table 1 enumerates these registries.  Section 4.3 discusses the XML
   Validation implications of these types of extensions.

5.2.  Extending Classes

   The classes of the EXTENSION type can extend the data model.  These
   container classes, collectively referred to as the extensible
   classes, are implemented with the iodef:ExtensionType data type in
   the schema.  They provide the ability to have new atomic or XML-
   encoded data elements in all of the top-level classes of the Incident
   class and a few of the more complicated subordinate classes.  As
   there are multiple instances of the extensible classes in the data
   model, there is discretion on where to add a new data element.  It is
   RECOMMENDED that the extension be placed in the most closely related
   class to the new information.

   Extensions using the atomic data types (i.e., all values of the dtype
   attributes other than "xml") MUST:

   1.  Set the element content of extensible class to the desired value,
       and

   2.  Set the dtype attribute to correspond to the data type of the
       element content.

   The following guidelines exist for extensions using XML:

   1.  The element content of the extensible class MUST be set to the
       desired value and the dtype attribute MUST be set to "xml".

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   2.  The extension schema MUST declare a separate namespace.  It is
       RECOMMENDED that these extensions have the prefix "iodef-".  This
       recommendation makes readability of the document easier by
       allowing the reader to infer which namespaces relate to IODEF by
       inspection.

   3.  It is RECOMMENDED that extension schemas follow the naming
       convention of the IODEF data model.  This makes reading an
       extended IODEF document look like any other IODEF document.  The
       names of all elements are capitalized.  For elements with
       composed names, a capital letter is used for each word.
       Attribute names are lower case.  Attributes with composed names
       are separated by a hyphen.

   4.  Parsers that encounter an unrecognized element in a namespace
       that they do support MUST reject the document as a syntax error.

   5.  There are security and performance implications in requiring
       implementations to dynamically download schemas at run time.
       Thus, implementations SHOULD NOT download schemas at runtime,
       unless implementations take appropriate precautions and are
       prepared for potentially significant network, processing, and
       time-out demands.

   6.  Some users of the IODEF may have private schema definitions that
       might not be available on the Internet.  In this situation, if a
       IODEF document leaks out of the private use space, references to
       some of those document schemas may not be resolvable.  This has
       two implications.  First, references to private schemas may never
       resolve.  As such, in addition to the suggestion that
       implementations do not download schemas at runtime mentioned
       above, recipients MUST be prepared for a schema definition in an
       IODEF document never to resolve.

   The following schema and XML document excerpt provide a template for
   an extension schema and its use in the IODEF document.

   This example schema defines a namespace of "iodef-extension1" and a
   single element named "newdata".

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     <xs:schema
        targetNamespace="iodef-extension1.xsd"
        xmlns:iodef-extension1="iodef-extension1.xsd"
        xmlns:xs="http://www.w3.org/2001/XMLSchema">
        attributeFormDefault="unqualified"
        elementFormDefault="qualified">
      <xs:import
           namespace="urn:ietf:params:xml:ns:iodef-1.0"
           schemaLocation=" urn:ietf:params:xml:schema:iodef-1.0"/>

        <xs:element name="newdata" type="xs:string" />
     </xs:schema>

   The following XML excerpt demonstrates the use of the above schema as
   an extension to the IODEF.

        <IODEF-Document
             version="2.00" lang="en-US"
             xmlns="urn:ietf:params:xml:ns:iodef-1.0"
             xmlns:iodef=" urn:ietf:params:xml:ns:iodef-1.0"
             xmlns:iodef-extension1="iodef-extension1.xsd"
             xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
             xsi:schemaLocation="iodef-extension1.xsd">
            <Incident purpose="reporting">
            ...
              <AdditionalData dtype="xml" meaning="xml">
                <iodef-extension1:newdata>
                 Field that could not be represented elsewhere
                </iodef-extension1:newdata>
              </AdditionalData>
            </Incident>
      </IODEF-Document

5.3.  Deconflicting Private Extensions

   Private extensions used in a document can be labeled to attribute
   their original specifier using the private-enum-name and private-
   enum-id attributes.  This allows a recipient of a document to
   disambiguate private extensions.  Only a single private extension can
   be identified in a given IODEF-Document.

   If a CSIRT has only a single private extension, then only the
   private-enum-name attribute needs to be specified.  Additional,
   multiple distinct private extensions or versioning of a single
   extension can be accomplished by also setting the corresponding
   private-num-id attribute.

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   The following XML excerpt demonstrates the specification of a private
   extension from "example.com" with an identifier of "13".

        <IODEF-Document
             version="2.00" lang="en-US"
             private-enum-name="example.com"
             private-enum-id="13"
            ...
      </IODEF-Document>

   If an unrecognized private extension is encountered in processing,
   the recipient MAY reject the entire document as a syntax error.

6.  Internationalization Issues

   Internationalization and localization is of specific concern to the
   IODEF, since it is only through collaboration, often across language
   barriers, that certain incidents be resolved and threat information
   shared.  The IODEF supports this goal by depending on XML constructs,
   and through explicit design choices in the data model.

   Since IODEF is implemented as an XML Schema, it implicitly supports
   all the different character encodings, such as UTF-8 and UTF-16,
   possible with XML.  Additionally, each IODEF document MUST specify
   the language in which their contents are encoded.  The language can
   be specified with the attribute "xml:lang" (per Section 2.12 of
   [W3C.XML]) in the top-level element (i.e., IODEF-Document) and
   letting all other elements inherit that definition.  All IODEF
   classes with a free-form text definition (i.e., all those defined of
   type iodef:MLStringType) can also specify a language different from
   the rest of the document.  The valid language codes for the
   "xml:lang" attribute are described in [RFC5646].

   The data model supports multiple translations of free-form text.  For
   classes where free-text is used for descriptive purposes (e.g.,
   classes of the iodef:MLStringType type such as the Description
   class), the given class always has a one-to-many cardinality to its
   parent.  The intent is to allow the identical text to be encoded in
   different instances of the same class, but each being in a different
   language.  This approach allows an IODEF document author to send
   recipients speaking different languages an identical document.  The
   IODEF parser SHOULD extract the appropriate language relevant to the
   recipient.

   Related instances of a given iodef:MLStringType class that are
   translations of each other are identified by a common identifier set
   in the translation-id attribute.  The example below shows three
   instances of a Description class expressed in three difference

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   languages.  The relationship between these three instances of the
   Description class is conveyed by the common value of "1" in the
   translation-id attribute.

   <IODEF-Document version="2.00" xml:lang="en" ...
     <Incident purpose="reporting">
       ...
       <Description translation-id="1"
                    xml:lang="en">English</Description>
       <Description translation-id="1"
                    xml:lang="de">Englisch</Description>
       <Description translation-id="1"
                    xml:lang="fr">Anglais</Description>

   While the intent of the data model is to provide internationalization
   and localization, the intent is not to do so at the detriment of
   interoperability.  While the IODEF does support different languages,
   the data model also relies heavily on standardized enumerated
   attributes that can crudely approximate the contents of the document.
   With this approach, a CSIRT should be able to make some sense of an
   IODEF document it receives even if the text based data elements are
   written in a language unfamiliar to the analyst.

7.  Examples

   This section provides examples of IODEF documents.  These examples do
   not necessarily represent the only way to encode particular
   information.

7.1.  Minimal Example

   A document containing only the mandatory elements and attributes.

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   <?xml version="1.0" encoding="UTF-8"?>
   <!-- Minimum IODEF document -->
   <IODEF-Document version="2.00" xml:lang="en"
      xmlns="urn:ietf:params:xml:ns:iodef-2.0"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation=
   "http://www.iana.org/assignments/xmlregistry/schema/
   iodef-2.0.xsd">
     <Incident purpose="reporting" restriction="private">
       <IncidentID name="csirt.example.com">492382</IncidentID>
       <GenerationTime>2015-07-18T09:00:00-05:00</GenerationTime>
       <Contact type="organization" role="creator">
         <Email>contact@csirt.example.com</Email>
       </Contact>
       <!-- Add more fields to make the document useful -->
     </Incident>
   </IODEF-Document>

7.2.  Indicators from a Campaign

   An example of C2 domains from a given campaign.

   <?xml version="1.0" encoding="UTF-8"?>
   <!-- A list of C2 domains associated with a campaign -->
   <IODEF-Document version="2.00" xml:lang="en"
      xmlns="urn:ietf:params:xml:ns:iodef-2.0"
      xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
      xsi:schemaLocation=
      "http://www.iana.org/assignments/xml-registry/schema/
       iodef-2.0.xsd">
     <Incident purpose="watch" restriction="green">
       <IncidentID name="csirt.example.com">897923</IncidentID>
         <RelatedActivity>
           <ThreatActor>
             <ThreatActorID>
             TA-12-AGGRESSIVE-BUTTERFLY
             </ThreatActorID>
             <Description>Aggressive Butterfly</Description>
           </ThreatActor>
           <Campaign>
             <CampaignID>C-2015-59405</CampaignID>
             <Description>Orange Giraffe</Description>
           </Campaign>
         </RelatedActivity>
         <GenerationTime>2015-10-02T11:18:00-05:00</GenerationTime>
         <Description>Summarizes the Indicators of Compromise
           for the Orange Giraffe campaign of the Aggressive

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           Butterfly crime gang.
         </Description>
         <Assessment>
           <BusinessImpact type="breach-proprietary"/>
         </Assessment>
         <Contact type="organization" role="creator">
           <ContactName>CSIRT for example.com</ContactName>
           <Email>contact@csirt.example.com</Email>
         </Contact>
         <IndicatorData>
           <Indicator>
             <IndicatorID name="csirt.example.com" version="1">
             G90823490
             </IndicatorID>
             <Description>C2 domains</Description>
             <StartTime>2014-12-02T11:18:00-05:00</StartTime>
             <Observable>
               <BulkObservable type="fqdn">
               <BulkObservableList>
                 kj290023j09r34.example.com
                 09ijk23jfj0k8.example.net
                 klknjwfjiowjefr923.example.org
                 oimireik79msd.example.org
               </BulkObservableList>
             </BulkObservable>
           </Observable>
         </Indicator>
       </IndicatorData>
     </Incident>
   </IODEF-Document>

7.3.  Incident Report

   An example of an incident report.

   ... TODO ...

8.  The IODEF Schema

  <?xml version="1.0"?>
  <xs:schema xmlns="urn:ietf:params:xml:ns:iodef-2.0"
             xmlns:iodef="urn:ietf:params:xml:ns:iodef-2.0"
             xmlns:enum="urn:ietf:params:xml:ns:iodef-enum-1.0"
             xmlns:sci="urn:ietf:params:xml:ns:iodef-sci-1.0"
             xmlns:xs="http://www.w3.org/2001/XMLSchema"
             xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
             targetNamespace="urn:ietf:params:xml:ns:iodef-2.0"

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             elementFormDefault="qualified"
             attributeFormDefault="unqualified">
    <xs:import namespace="http://www.w3.org/2000/09/xmldsig#"
               schemaLocation="http://www.w3.org/TR/2002/
  REC-xmldsig-core-20020212/xmldsig-core-schema.xsd"/>
    <xs:import namespace="urn:ietf:params:xml:ns:iodef-enum-1.0"
               schemaLocation="http://www.iana.org/assignments/
  xml-registry/schema/iodef-enum-1.0.xsd"/>
    <xs:import namespace="urn:ietf:params:xml:ns:iodef-sci-1.0"
               schemaLocation="http://www.iana.org/assignments/
  xml-registry/schema/iodef-sci-1.0.xsd"/>
    <xs:import namespace="http://www.w3.org/XML/1998/namespace"
               schemaLocation="http://www.w3c.org/2001/xml.xsd"/>
    <xs:annotation>
      <xs:documentation>
         Incident Object Description Exchange Format v2.0, RFC5070bis
      </xs:documentation>
    </xs:annotation>
    <!--
     ===================================================================
     == IODEF-Document class                                          ==
     ===================================================================
    -->
    <xs:element name="IODEF-Document">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Incident" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="version" type="xs:string" fixed="2.00"/>
        <xs:attribute ref="xml:lang"/>
        <xs:attribute name="format-id" type="xs:string" use="optional"/>
        <xs:attribute name="private-enum-name"
                      type="xs:string" use="optional"/>
        <xs:attribute name="private-enum-id"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     == Incident class                                                ==
     ===================================================================
    -->
    <xs:element name="Incident">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IncidentID"/>

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          <xs:element ref="iodef:AlternativeID" minOccurs="0"/>
          <xs:element ref="iodef:RelatedActivity"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DetectTime" minOccurs="0"/>
          <xs:element ref="iodef:StartTime" minOccurs="0"/>
          <xs:element ref="iodef:EndTime" minOccurs="0"/>
          <xs:element ref="iodef:RecoveryTime" minOccurs="0"/>
          <xs:element ref="iodef:ReportTime" minOccurs="0"/>
          <xs:element ref="iodef:GenerationTime"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Discovery"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Assessment"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Method"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Contact" maxOccurs="unbounded"/>
          <xs:element ref="iodef:EventData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:IndicatorData" minOccurs="0"/>
          <xs:element ref="iodef:History" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="purpose"
                      type="incident-purpose-type" use="required"/>
        <xs:attribute name="ext-purpose"
                      type="xs:string" use="optional"/>
        <xs:attribute name="status" type="incident-status-type"/>
        <xs:attribute name="ext-status"
                      type="xs:string" use="optional"/>
        <xs:attribute ref="xml:lang"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" default="private"
                      use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="incident-purpose-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="traceback"/>
        <xs:enumeration value="mitigation"/>
        <xs:enumeration value="reporting"/>
        <xs:enumeration value="watch"/>
        <xs:enumeration value="other"/>

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        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="incident-status-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="new"/>
        <xs:enumeration value="in-progress"/>
        <xs:enumeration value="forwarded"/>
        <xs:enumeration value="resolved"/>
        <xs:enumeration value="future"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <!--
     ===================================================================
     ==  IncidentID class                                             ==
     ===================================================================
    -->
    <xs:element name="IncidentID" type="iodef:IncidentIDType"/>
    <xs:complexType name="IncidentIDType">
      <xs:simpleContent>
        <xs:extension base="xs:string">
          <xs:attribute name="name" type="xs:string" use="required"/>
          <xs:attribute name="instance"
                        type="xs:string" use="optional"/>
          <xs:attribute name="restriction"
                        type="iodef:restriction-type" use="optional"/>
          <xs:attribute name="ext-restriction"
                        type="xs:string" use="optional"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
    <!--
     ==================================================================
     ==  AlternativeID class                                         ==
     ==================================================================
    -->
    <xs:element name="AlternativeID">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IncidentID" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>

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    <!--
     ===================================================================
     ==  RelatedActivity class                                        ==
     ===================================================================
    -->
    <xs:element name="RelatedActivity">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IncidentID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:ThreatActor"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Campaign"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Confidence" minOccurs="0"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="ThreatActor">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:ThreatActorID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:URL" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="ThreatActorID" type="xs:string"/>
    <xs:element name="Campaign">
      <xs:complexType>

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        <xs:sequence>
          <xs:element ref="iodef:CampaignID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="CampaignID" type="xs:string"/>
    <!--
     ===================================================================
     ==   Contact class                                               ==
     ===================================================================
    -->
    <xs:element name="Contact">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:ContactName"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:ContactTitle"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:RegistryHandle"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:PostalAddress"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Email"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Telephone"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Timezone" minOccurs="0"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="role"
                      type="contact-role-type" use="required"/>
        <xs:attribute name="ext-role"
                      type="xs:string" use="optional"/>
        <xs:attribute name="type"

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                      type="contact-type-type" use="required"/>
        <xs:attribute name="ext-type"
                      type="xs:string" use="optional"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="contact-role-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="creator"/>
        <xs:enumeration value="reporter"/>
        <xs:enumeration value="admin"/>
        <xs:enumeration value="tech"/>
        <xs:enumeration value="provider"/>
        <xs:enumeration value="zone"/>
        <xs:enumeration value="user"/>
        <xs:enumeration value="billing"/>
        <xs:enumeration value="legal"/>
        <xs:enumeration value="abuse"/>
        <xs:enumeration value="irt"/>
        <xs:enumeration value="cc"/>
        <xs:enumeration value="cc-irt"/>
        <xs:enumeration value="leo"/>
        <xs:enumeration value="vendor"/>
        <xs:enumeration value="vendor-services"/>
        <xs:enumeration value="victim"/>
        <xs:enumeration value="victim-notified"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="contact-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="person"/>
        <xs:enumeration value="organization"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="ContactName" type="iodef:MLStringType"/>
    <xs:element name="ContactTitle" type="iodef:MLStringType"/>
    <xs:element name="RegistryHandle">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:string">
            <xs:attribute name="registry"
                          type="registryhandle-registry-type"/>
            <xs:attribute name="ext-registry"

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                          type="xs:string" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="registryhandle-registry-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="internic"/>
        <xs:enumeration value="apnic"/>
        <xs:enumeration value="arin"/>
        <xs:enumeration value="lacnic"/>
        <xs:enumeration value="ripe"/>
        <xs:enumeration value="afrinic"/>
        <xs:enumeration value="local"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="PostalAddress">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:PAddress"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="type"
                      type="postaladdress-type-type" use="optional"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="PAddress" type="iodef:MLStringType"/>
    <xs:simpleType name="postaladdress-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="street"/>
        <xs:enumeration value="mailing"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="Telephone">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:TelephoneNumber"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="type"
                      type="telephone-type-type" use="optional"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>

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    </xs:element>
    <xs:element name="TelephoneNumber" type="xs:string"/>
    <xs:simpleType name="telephone-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="direct"/>
        <xs:enumeration value="mobile"/>
        <xs:enumeration value="fax"/>
        <xs:enumeration value="hotline"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="Email">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:EmailTo"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="type"
                      type="email-type-type" use="optional"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="email-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="direct"/>
        <xs:enumeration value="hotline"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <!--
     ===================================================================
     ==  Time-based classes                                           ==
     ===================================================================
    -->
    <xs:element name="DateTime" type="xs:dateTime"/>
    <xs:element name="ReportTime" type="xs:dateTime"/>
    <xs:element name="DetectTime" type="xs:dateTime"/>
    <xs:element name="StartTime" type="xs:dateTime"/>
    <xs:element name="EndTime" type="xs:dateTime"/>
    <xs:element name="RecoveryTime" type="xs:dateTime"/>
    <xs:element name="GenerationTime" type="xs:dateTime"/>
    <xs:element name="Timezone" type="iodef:TimezoneType"/>
    <!--
     ===================================================================
     ==  History class                                                ==
     ===================================================================
    -->

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    <xs:element name="History">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:HistoryItem" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="HistoryItem">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:DateTime"/>
          <xs:element ref="iodef:IncidentID" minOccurs="0"/>
          <xs:element ref="iodef:Contact" minOccurs="0"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DefinedCOA"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="action"
                      type="iodef:action-type" use="required"/>
        <xs:attribute name="ext-action"
                      type="xs:string" use="optional"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="DefinedCOA" type="iodef:MLStringType"/>
    <!--
     ===================================================================
     ==  Expectation class                                            ==
     ===================================================================
    -->
    <xs:element name="Expectation">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DefinedCOA"
                      minOccurs="0" maxOccurs="unbounded"/>

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          <xs:element ref="iodef:StartTime" minOccurs="0"/>
          <xs:element ref="iodef:EndTime" minOccurs="0"/>
          <xs:element ref="iodef:Contact" minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="action"
                      type="iodef:action-type" default="other"/>
        <xs:attribute name="ext-action"
                      type="xs:string" use="optional"/>
        <xs:attribute name="severity" type="iodef:severity-type"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     ==  Discovery class                                              ==
     ===================================================================
    -->
    <xs:element name="Discovery">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DetectionPattern"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="source"
                      type="discovery-source-type" use="optional"
                      default="unknown"/>
        <xs:attribute name="ext-source"
                      type="xs:string" use="optional"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="discovery-source-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="nidps"/>
        <xs:enumeration value="hips"/>
        <xs:enumeration value="siem"/>
        <xs:enumeration value="av"/>

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        <xs:enumeration value="third-party-monitoring"/>
        <xs:enumeration value="incident"/>
        <xs:enumeration value="os-log"/>
        <xs:enumeration value="application-log"/>
        <xs:enumeration value="device-log"/>
        <xs:enumeration value="network-flow"/>
        <xs:enumeration value="passive-dns"/>
        <xs:enumeration value="investigation"/>
        <xs:enumeration value="audit"/>
        <xs:enumeration value="internal-notification"/>
        <xs:enumeration value="external-notification"/>
        <xs:enumeration value="leo"/>
        <xs:enumeration value="partner"/>
        <xs:enumeration value="actor"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="DetectionPattern">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Application"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element name="DetectionConfiguration"
                      type="xs:string"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     ==  Method class                                                 ==
     ===================================================================
    -->
    <xs:element name="Method">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Reference"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="sci:AttackPattern"
                      minOccurs="0" maxOccurs="unbounded"/>

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          <xs:element ref="sci:Vulnerability"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="sci:Weakness"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     ==  Reference class                                              ==
     ===================================================================
    -->
    <xs:element name="Reference">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="enum:ReferenceName" minOccurs="0"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     ==  Assessment class                                             ==
     ===================================================================
    -->
    <xs:element name="Assessment">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IncidentCategory"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:choice maxOccurs="unbounded">
            <xs:element ref="iodef:SystemImpact"/>
            <xs:element ref="iodef:BusinessImpact"/>
            <xs:element ref="iodef:TimeImpact"/>
            <xs:element ref="iodef:MonetaryImpact"/>
            <xs:element ref="iodef:IntendedImpact"/>
          </xs:choice>
          <xs:element ref="iodef:Counter"

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                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:MitigatingFactor"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Cause"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Confidence" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="occurrence">
          <xs:simpleType>
            <xs:restriction base="xs:NMTOKEN">
              <xs:enumeration value="actual"/>
              <xs:enumeration value="potential"/>
            </xs:restriction>
          </xs:simpleType>
        </xs:attribute>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="IncidentCategory" type="iodef:MLStringType"/>
    <xs:element name="BusinessImpact" type="iodef:BusinessImpactType"/>
    <xs:element name="IntendedImpact" type="iodef:BusinessImpactType"/>
    <xs:element name="MitigatingFactor" type="iodef:MLStringType"/>
    <xs:element name="Cause" type="iodef:MLStringType"/>
    <xs:element name="SystemImpact">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="severity"
                      type="iodef:severity-type" use="optional"/>
        <xs:attribute name="completion"
                      type="iodef:systemimpact-completion-type"
                      use="optional"/>
        <xs:attribute name="type"
                      type="systemimpact-type-type"
                      use="optional" default="unknown"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="systemimpact-completion-type">
      <xs:restriction base="xs:NMTOKEN">

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        <xs:enumeration value="failed"/>
        <xs:enumeration value="succeeded"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="systemimpact-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="takeover-account"/>
        <xs:enumeration value="takeover-service"/>
        <xs:enumeration value="takeover-system"/>
        <xs:enumeration value="cps-manipulation"/>
        <xs:enumeration value="cps-damage"/>
        <xs:enumeration value="availability-data"/>
        <xs:enumeration value="availability-account"/>
        <xs:enumeration value="availability-service"/>
        <xs:enumeration value="availability-system"/>
        <xs:enumeration value="damaged-system"/>
        <xs:enumeration value="damaged-data"/>
        <xs:enumeration value="breach-proprietary"/>
        <xs:enumeration value="breach-privacy"/>
        <xs:enumeration value="breach-credential"/>
        <xs:enumeration value="breach-configuration"/>
        <xs:enumeration value="integrity-data"/>
        <xs:enumeration value="integrity-configuration"/>
        <xs:enumeration value="integrity-hardware"/>
        <xs:enumeration value="traffic-redirection"/>
        <xs:enumeration value="monitoring-traffic"/>
        <xs:enumeration value="monitoring-host"/>
        <xs:enumeration value="policy"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:complexType name="BusinessImpactType">
      <xs:sequence>
        <xs:element ref="iodef:Description"
                    minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
      <xs:attribute name="severity"
                    type="businessimpact-severity-type" use="optional"/>
      <xs:attribute name="ext-severity"
                    type="xs:string" use="optional"/>
      <xs:attribute name="type"
                    type="businessimpact-type-type"
                    use="optional" default="unknown"/>
      <xs:attribute name="ext-type" type="xs:string" use="optional"/>
    </xs:complexType>
    <xs:simpleType name="businessimpact-severity-type">
      <xs:restriction base="xs:NMTOKEN">

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        <xs:enumeration value="none"/>
        <xs:enumeration value="low"/>
        <xs:enumeration value="medium"/>
        <xs:enumeration value="high"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="businessimpact-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="breach-proprietary"/>
        <xs:enumeration value="breach-privacy"/>
        <xs:enumeration value="breach-credential"/>
        <xs:enumeration value="loss-of-integrity"/>
        <xs:enumeration value="loss-of-service"/>
        <xs:enumeration value="theft-financial"/>
        <xs:enumeration value="theft-service"/>
        <xs:enumeration value="degraded-reputation"/>
        <xs:enumeration value="asset-damage"/>
        <xs:enumeration value="asset-manipulation"/>
        <xs:enumeration value="legal"/>
        <xs:enumeration value="extortion"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="TimeImpact">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="iodef:PositiveFloatType">
            <xs:attribute name="severity" type="iodef:severity-type"/>
            <xs:attribute name="metric"
                          type="timeimpact-metric-type" use="required"/>
            <xs:attribute name="ext-metric"
                          type="xs:string" use="optional"/>
            <xs:attribute name="duration" type="iodef:duration-type"/>
            <xs:attribute name="ext-duration"
                          type="xs:string" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="timeimpact-metric-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="labor"/>
        <xs:enumeration value="elapsed"/>
        <xs:enumeration value="downtime"/>
        <xs:enumeration value="ext-value"/>

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      </xs:restriction>
    </xs:simpleType>
    <xs:element name="MonetaryImpact">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="iodef:PositiveFloatType">
            <xs:attribute name="severity" type="iodef:severity-type"/>
            <xs:attribute name="currency" type="xs:string"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:element name="Confidence">
      <xs:complexType>
        <xs:attribute name="rating"
                      type="confidence-rating-type" use="required"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="confidence-rating-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="low"/>
        <xs:enumeration value="medium"/>
        <xs:enumeration value="high"/>
        <xs:enumeration value="numeric"/>
        <xs:enumeration value="unknown"/>
      </xs:restriction>
    </xs:simpleType>
    <!--
     ===================================================================
     == EventData class                                               ==
     ===================================================================
    -->
    <xs:element name="EventData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DetectTime" minOccurs="0"/>
          <xs:element ref="iodef:StartTime" minOccurs="0"/>
          <xs:element ref="iodef:EndTime" minOccurs="0"/>
          <xs:element ref="iodef:RecoveryTime" minOccurs="0"/>
          <xs:element ref="iodef:ReportTime" minOccurs="0"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Discovery"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Assessment" minOccurs="0"/>
          <xs:element ref="iodef:Method"

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                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Flow"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Expectation"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Record" minOccurs="0"/>
          <xs:element ref="iodef:EventData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     ==  Flow class                                                   ==
     ===================================================================
    -->
    <xs:element name="Flow">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:System" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     ==  System class                                                 ==
     ===================================================================
    -->
    <xs:element name="System">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Node"/>
          <xs:element ref="iodef:NodeRole"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Service"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:OperatingSystem"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Counter"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element name="AssetID"

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                      type="xs:string"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="category" type="system-category-type"/>
        <xs:attribute name="ext-category"
                      type="xs:string" use="optional"/>
        <xs:attribute name="interface" type="xs:string"/>
        <xs:attribute name="spoofed"
                      type="yes-no-unknown-type" default="unknown"/>
        <xs:attribute name="virtual"
                      type="yes-no-unknown-type" use="optional"
                      default="unknown"/>
        <xs:attribute name="ownership" type="system-ownership-type"
                      use="optional"/>
        <xs:attribute name="ext-ownership"
                      type="xs:string" use="optional"/>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="OperatingSystem" type="iodef:SoftwareType"/>
    <xs:simpleType name="system-category-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="source"/>
        <xs:enumeration value="target"/>
        <xs:enumeration value="intermediate"/>
        <xs:enumeration value="sensor"/>
        <xs:enumeration value="infrastructure"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="system-ownership-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="organization"/>
        <xs:enumeration value="personal"/>
        <xs:enumeration value="partner"/>
        <xs:enumeration value="customer"/>
        <xs:enumeration value="no-relationship"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>

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    <!--
     ==================================================================
     == Node class                                                   ==
     ==================================================================
    -->
    <xs:element name="Node">
      <xs:complexType>
        <xs:sequence>
          <xs:choice maxOccurs="unbounded">
            <xs:element ref="iodef:DomainData"
                        minOccurs="0" maxOccurs="unbounded"/>
            <xs:element ref="iodef:Address"
                        minOccurs="0" maxOccurs="unbounded"/>
          </xs:choice>
          <xs:element ref="iodef:PostalAddress" minOccurs="0"/>
          <xs:element ref="iodef:Location"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Counter"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="Address">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:string">
            <xs:attribute name="category"
                          type="address-category-type"
                          default="ipv6-addr"/>
            <xs:attribute name="ext-category"
                          type="xs:string" use="optional"/>
            <xs:attribute name="vlan-name" type="xs:string"/>
            <xs:attribute name="vlan-num" type="xs:integer"/>
            <xs:attribute name="observable-id"
                          type="xs:ID" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="address-category-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="asn"/>
        <xs:enumeration value="atm"/>
        <xs:enumeration value="e-mail"/>
        <xs:enumeration value="mac"/>
        <xs:enumeration value="ipv4-addr"/>
        <xs:enumeration value="ipv4-net"/>
        <xs:enumeration value="ipv4-net-mask"/>

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        <xs:enumeration value="ipv6-addr"/>
        <xs:enumeration value="ipv6-net"/>
        <xs:enumeration value="ipv6-net-mask"/>
        <xs:enumeration value="site-uri"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="Location" type="iodef:MLStringType"/>
    <xs:element name="NodeRole">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="category"
                      type="noderole-category-type" use="required"/>
        <xs:attribute name="ext-category"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="noderole-category-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="client"/>
        <xs:enumeration value="client-enterprise"/>
        <xs:enumeration value="client-partner"/>
        <xs:enumeration value="client-remote"/>
        <xs:enumeration value="client-kiosk"/>
        <xs:enumeration value="client-mobile"/>
        <xs:enumeration value="server-internal"/>
        <xs:enumeration value="server-public"/>
        <xs:enumeration value="www"/>
        <xs:enumeration value="mail"/>
        <xs:enumeration value="webmail"/>
        <xs:enumeration value="messaging"/>
        <xs:enumeration value="streaming"/>
        <xs:enumeration value="voice"/>
        <xs:enumeration value="file"/>
        <xs:enumeration value="ftp"/>
        <xs:enumeration value="p2p"/>
        <xs:enumeration value="name"/>
        <xs:enumeration value="directory"/>
        <xs:enumeration value="credential"/>
        <xs:enumeration value="print"/>
        <xs:enumeration value="application"/>
        <xs:enumeration value="database"/>
        <xs:enumeration value="backup"/>
        <xs:enumeration value="dhcp"/>
        <xs:enumeration value="assessment"/>

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        <xs:enumeration value="source-control"/>
        <xs:enumeration value="config-management"/>
        <xs:enumeration value="monitoring"/>
        <xs:enumeration value="infra"/>
        <xs:enumeration value="infra-firewall"/>
        <xs:enumeration value="infra-router"/>
        <xs:enumeration value="infra-switch"/>
        <xs:enumeration value="camera"/>
        <xs:enumeration value="proxy"/>
        <xs:enumeration value="remote-access"/>
        <xs:enumeration value="log"/>
        <xs:enumeration value="virtualization"/>
        <xs:enumeration value="pos"/>
        <xs:enumeration value="scada"/>
        <xs:enumeration value="scada-supervisory"/>
        <xs:enumeration value="sinkhole"/>
        <xs:enumeration value="honeypot"/>
        <xs:enumeration value="anonymization"/>
        <xs:enumeration value="c2-server"/>
        <xs:enumeration value="malware-distribution"/>
        <xs:enumeration value="drop-server"/>
        <xs:enumeration value="hop-point"/>
        <xs:enumeration value="reflector"/>
        <xs:enumeration value="phishing-site"/>
        <xs:enumeration value="spear-phishing-site"/>
        <xs:enumeration value="recruiting-site"/>
        <xs:enumeration value="fraudulent-site"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <!--
     ===================================================================
     ==  Service Class                                                ==
     ===================================================================
    -->
    <xs:element name="Service">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:ServiceName" minOccurs="0"/>
          <xs:choice minOccurs="0">
            <xs:element ref="iodef:Port"/>
            <xs:element ref="iodef:Portlist"/>
          </xs:choice>
          <xs:element ref="iodef:ProtoType" minOccurs="0"/>
          <xs:element ref="iodef:ProtoCode" minOccurs="0"/>
          <xs:element ref="iodef:ProtoField" minOccurs="0"/>
          <xs:element ref="iodef:ApplicationHeader" minOccurs="0"/>
          <xs:element ref="iodef:EmailData" minOccurs="0"/>

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          <xs:element ref="iodef:Application" minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="ip-protocol"
                      type="xs:integer" use="required"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Port" type="xs:integer"/>
    <xs:element name="Portlist" type="iodef:PortlistType"/>
    <xs:element name="ProtoType" type="xs:integer"/>
    <xs:element name="ProtoCode" type="xs:integer"/>
    <xs:element name="ProtoField" type="xs:integer"/>
    <xs:element name="ApplicationHeader">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:ApplicationHeaderField"
                      maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="ApplicationHeaderField"
                type="iodef:ExtensionType"/>
    <xs:element name="ServiceName">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IANAService"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="IANAService" type="xs:string"/>
    <xs:element name="Application" type="iodef:SoftwareType"/>
    <!--
     ===================================================================
     ==  Counter class                                                ==
     ===================================================================
    -->
    <xs:element name="Counter">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:float">
            <xs:attribute name="type"
                          type="counter-type-type" use="required"/>
            <xs:attribute name="ext-type"
                          type="xs:string" use="optional"/>

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            <xs:attribute name="unit"
                          type="counter-unit-type" use="required"/>
            <xs:attribute name="ext-unit"
                          type="xs:string" use="optional"/>
            <xs:attribute name="meaning"
                          type="xs:string" use="optional"/>
            <xs:attribute name="duration" type="iodef:duration-type"/>
            <xs:attribute name="ext-duration"
                          type="xs:string" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="counter-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="counter"/>
        <xs:enumeration value="rate"/>
        <xs:enumeration value="average"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="counter-unit-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="byte"/>
        <xs:enumeration value="mbit"/>
        <xs:enumeration value="packet"/>
        <xs:enumeration value="flow"/>
        <xs:enumeration value="session"/>
        <xs:enumeration value="event"/>
        <xs:enumeration value="alert"/>
        <xs:enumeration value="message"/>
        <xs:enumeration value="host"/>
        <xs:enumeration value="site"/>
        <xs:enumeration value="organization"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <!--
     ===================================================================
     ==  EmailData class                                              ==
     ===================================================================
    -->
    <xs:element name="EmailData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:EmailTo" minOccurs="0"/>
          <xs:element ref="iodef:EmailFrom" minOccurs="0"/>
          <xs:element ref="iodef:EmailSubject" minOccurs="0"/>

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          <xs:element ref="iodef:EmailX-Mailer" minOccurs="0"/>
          <xs:element ref="iodef:EmailHeaderField" minOccurs="0"/>
          <xs:element ref="iodef:HashData" minOccurs="0"/>
          <xs:element ref="SignatureData" minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="EmailTo" type="xs:string"/>
    <xs:element name="EmailFrom" type="xs:string"/>
    <xs:element name="EmailSubject" type="xs:string"/>
    <xs:element name="EmailX-Mailer" type="xs:string"/>
    <xs:element name="EmailHeaderField" type="iodef:ExtensionType"/>
    <!--
     ===================================================================
     ==   DomainData class                                            ==
     ===================================================================
    -->
    <xs:element name="DomainData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Name" maxOccurs="1"/>
          <xs:element ref="iodef:DateDomainWasChecked"
                      minOccurs="0" maxOccurs="1"/>
          <xs:element ref="iodef:RegistrationDate"
                      minOccurs="0" maxOccurs="1"/>
          <xs:element ref="iodef:ExpirationDate"
                      minOccurs="0" maxOccurs="1"/>
          <xs:element ref="iodef:RelatedDNS"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Nameservers"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:DomainContacts"
                      minOccurs="0" maxOccurs="1"/>
        </xs:sequence>
        <xs:attribute name="system-status"
                      type="domaindata-system-status-type"/>
        <xs:attribute name="ext-system-status"
                      type="xs:string" use="optional"/>
        <xs:attribute name="domain-status"
                      type="domaindata-domain-status-type"/>
        <xs:attribute name="ext-domain-status"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Name" type="xs:string"/>
    <xs:element name="DateDomainWasChecked" type="xs:dateTime"/>

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    <xs:element name="RegistrationDate" type="xs:dateTime"/>
    <xs:element name="ExpirationDate" type="xs:dateTime"/>
    <xs:simpleType name="domaindata-system-status-type">
      <xs:restriction base="xs:string">
        <xs:enumeration value="spoofed"/>
        <xs:enumeration value="fraudulent"/>
        <xs:enumeration value="innocent-hacked"/>
        <xs:enumeration value="innocent-hijacked"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="domaindata-domain-status-type">
      <xs:restriction base="xs:string">
        <xs:enumeration value="reservedDelegation"/>
        <xs:enumeration value="assignedAndActive"/>
        <xs:enumeration value="assignedAndInactive"/>
        <xs:enumeration value="assignedAndOnHold"/>
        <xs:enumeration value="revoked"/>
        <xs:enumeration value="transferPending"/>
        <xs:enumeration value="registryLock"/>
        <xs:enumeration value="registrarLock"/>
        <xs:enumeration value="other"/>
        <xs:enumeration value="unknown"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="RelatedDNS" type="iodef:ExtensionType"/>
    <xs:element name="Nameservers">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Server"/>
          <xs:element ref="iodef:Address" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="Server" type="xs:string"/>
    <xs:element name="DomainContacts">
      <xs:complexType>
        <xs:choice>
          <xs:element ref="iodef:SameDomainContact"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="1" maxOccurs="unbounded"/>
        </xs:choice>
      </xs:complexType>
    </xs:element>
    <xs:element name="SameDomainContact" type="xs:string"/>
    <!--

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     ===================================================================
     ==  Record class                                                 ==
     ===================================================================
    -->
    <xs:element name="Record">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:RecordData" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="RecordData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:DateTime" minOccurs="0"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Application" minOccurs="0"/>
          <xs:element ref="iodef:RecordPattern"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:RecordItem" maxOccurs="unbounded"/>
          <xs:element ref="iodef:FileData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:WindowsRegistryKeysModified"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:CertificateData"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="RecordPattern">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:string">
            <xs:attribute name="type"
                          type="recordpattern-type-type"
                          use="required"/>

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            <xs:attribute name="ext-type"
                          type="xs:string" use="optional"/>
            <xs:attribute name="offset"
                          type="xs:integer" use="optional"/>
            <xs:attribute name="offsetunit"
                          type="recordpattern-offsetunit-type"
                          use="optional" default="line"/>
            <xs:attribute name="ext-offsetunit"
                          type="xs:string" use="optional"/>
            <xs:attribute name="instance"
                          type="xs:integer" use="optional"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="recordpattern-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="regex"/>
        <xs:enumeration value="binary"/>
        <xs:enumeration value="xpath"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="recordpattern-offsetunit-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="line"/>
        <xs:enumeration value="byte"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="RecordItem" type="iodef:ExtensionType"/>
    <!--
     ===================================================================
     ==  WindowsRegistryKeysModified Class                            ==
     ===================================================================
    -->
    <xs:element name="WindowsRegistryKeysModified">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Key" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Key">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:KeyName"/>

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          <xs:element ref="iodef:Value" minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="registryaction"
                      type="key-registryaction-type"/>
        <xs:attribute name="ext-registryaction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="KeyName" type="xs:string"/>
    <xs:element name="Value" type="xs:string"/>
    <xs:simpleType name="key-registryaction-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="add-key"/>
        <xs:enumeration value="add-value"/>
        <xs:enumeration value="delete-key"/>
        <xs:enumeration value="delete-value"/>
        <xs:enumeration value="modify-key"/>
        <xs:enumeration value="modify-value"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <!--
    ====================================================================
    ==  FileData Class                                                ==
    ====================================================================
    -->
    <xs:element name="FileData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:File"
                      minOccurs="1" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="File">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:FileName" minOccurs="0"/>
          <xs:element ref="iodef:FileSize" minOccurs="0"/>
          <xs:element ref="FileType" minOccurs="0"/>
          <xs:element ref="iodef:URL"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:HashData" minOccurs="0"/>

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          <xs:element ref="iodef:SignatureData" minOccurs="0"/>
          <xs:element ref="iodef:AssociatedSoftware" minOccurs="0"/>
          <xs:element ref="iodef:FileProperties"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="FileName" type="xs:string"/>
    <xs:element name="FileSize" type="xs:integer"/>
    <xs:element name="FileType" type="xs:integer"/>
    <xs:element name="AssociatedSoftware" type="iodef:SoftwareType"/>
    <xs:element name="FileProperties" type="iodef:ExtensionType"/>
    <!--
    ====================================================================
    ==  HashData Class                                                ==
    ====================================================================
    -->
    <xs:element name="HashData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:HashTarget" minOccurs="0"/>
          <xs:element ref="iodef:Hash"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:FuzzyHash"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="scope"
                      type="hashdata-scope-type" use="required"/>
        <xs:attribute name="ext-scope" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="HashTarget" type="iodef:MLStringType"/>
    <xs:simpleType name="hashdata-scope-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="file-contents"/>
        <xs:enumeration value="file-pe-section"/>
        <xs:enumeration value="file-pe-iat"/>
        <xs:enumeration value="file-pe-resource"/>
        <xs:enumeration value="file-pdf-object"/>
        <xs:enumeration value="email-hash"/>
        <xs:enumeration value="email-headers-hash"/>
        <xs:enumeration value="email-body-hash"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="Hash">
      <xs:complexType>

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        <xs:sequence>
          <xs:element ref="ds:DigestMethod"/>
          <xs:element ref="ds:DigestValue"/>
          <xs:element ref="ds:CanonicalizationMethod"/>
          <xs:element ref="iodef:Application" minOccurs="0"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="FuzzyHash">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:AdditionalData"/>
          <xs:element ref="iodef:Application" minOccurs="0"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     ==  SignatureData Class                                          ==
     ===================================================================
    -->
    <xs:element name="SignatureData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="ds:Signature" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     ==  CertificateData                                              ==
     ===================================================================
    -->
    <xs:element name="CertificateData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Certificate" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Certificate">
      <xs:complexType>
        <xs:sequence>

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          <xs:element ref="ds:X509Data"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
      </xs:complexType>
    </xs:element>
    <!--
     ===================================================================
     == IndicatorData Class                                           ==
     ===================================================================
    -->
    <xs:element name="IndicatorData">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Indicator"
                      minOccurs="1" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="Indicator">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IndicatorID"/>
          <xs:element ref="iodef:AlternativeIndicatorID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:StartTime" minOccurs="0"/>
          <xs:element ref="iodef:EndTime" minOccurs="0"/>
          <xs:element ref="iodef:Confidence" minOccurs="0"/>
          <xs:element ref="iodef:Contact"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:choice>
            <xs:element ref="iodef:Observable"/>
            <xs:element ref="iodef:ObservableReference"/>
            <xs:element ref="iodef:IndicatorExpression"/>
            <xs:element ref="iodef:IndicatorReference"/>
          </xs:choice>
          <xs:element ref="iodef:NodeRole"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AttackPhase"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>

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        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="IndicatorID">
      <xs:complexType>
        <xs:simpleContent>
          <xs:extension base="xs:ID">
            <xs:attribute name="name" type="xs:string" use="required"/>
            <xs:attribute name="version"
                          type="xs:string" use="required"/>
          </xs:extension>
        </xs:simpleContent>
      </xs:complexType>
    </xs:element>
    <xs:element name="AlternativeIndicatorID">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:IndicatorID" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="Observable">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Address" minOccurs="0"/>
          <xs:element ref="iodef:DomainData" minOccurs="0"/>
          <xs:element ref="iodef:EmailData" minOccurs="0"/>
          <xs:element ref="iodef:WindowsRegistryKeysModified"
                           minOccurs="0"/>
          <xs:element ref="iodef:FileData" minOccurs="0"/>
          <xs:element ref="iodef:CertificateData" minOccurs="0"/>
          <xs:element ref="iodef:RegistryHandle" minOccurs="0"/>
          <xs:element ref="iodef:RecordData" minOccurs="0"/>
          <xs:element ref="iodef:EventData" minOccurs="0"/>
          <xs:element ref="iodef:Incident" minOccurs="0"/>
          <xs:element ref="iodef:Expectation" minOccurs="0"
                      maxOccurs="unbounded"/>
          <xs:element ref="Reference"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Assessment" minOccurs="0"/>
          <xs:element ref="iodef:HistoryItem" minOccurs="0"/>
          <xs:element ref="iodef:BulkObservable" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData" minOccurs="0"/>

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        </xs:sequence>
        <xs:attribute name="restriction"
                      type="iodef:restriction-type" use="optional"/>
        <xs:attribute name="ext-restriction"
                      type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="BulkObservable">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:BulkObservableFormat" minOccurs="0"/>
          <xs:element name="BulkObservableList"
                      type="xs:string" minOccurs="0"/>
        </xs:sequence>
        <xs:attribute name="type"
                      type="observable-type-type" use="required"/>
        <xs:attribute name="ext-type" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="observable-type-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="asn"/>
        <xs:enumeration value="atm"/>
        <xs:enumeration value="e-mail"/>
        <xs:enumeration value="ipv4-addr"/>
        <xs:enumeration value="ipv4-net"/>
        <xs:enumeration value="ipv4-net-mask"/>
        <xs:enumeration value="ipv6-addr"/>
        <xs:enumeration value="ipv6-net"/>
        <xs:enumeration value="ipv6-net-mask"/>
        <xs:enumeration value="mac"/>
        <xs:enumeration value="site-uri"/>
        <xs:enumeration value="fqdn"/>
        <xs:enumeration value="doman-name"/>
        <xs:enumeration value="domain-to-ipv4"/>
        <xs:enumeration value="domain-to-ipv6"/>
        <xs:enumeration value="domain-to-ipv4-timestamp"/>
        <xs:enumeration value="domain-to-ipv6-timestamp"/>
        <xs:enumeration value="ipv4-port"/>
        <xs:enumeration value="ipv6-port"/>
        <xs:enumeration value="windows-reg-key"/>
        <xs:enumeration value="file-hash"/>
        <xs:enumeration value="email-x-mailer"/>
        <xs:enumeration value="email-subject"/>
        <xs:enumeration value="http-user-agent"/>
        <xs:enumeration value="http-request-uri"/>
        <xs:enumeration value="mutex"/>
        <xs:enumeration value="file-path"/>

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        <xs:enumeration value="user-name"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="BulkObservableFormat">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:Hash" minOccurs="0"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="IndicatorExpression">
      <xs:complexType>
        <xs:sequence>
          <xs:choice>
            <xs:element ref="iodef:IndicatorExpression" minOccurs="0"/>
            <xs:element ref="iodef:Observable" minOccurs="0"/>
            <xs:element ref="iodef:ObservableReference" minOccurs="0"/>
            <xs:element ref="iodef:IndicatorReference" minOccurs="0"/>
          </xs:choice>
          <xs:element ref="iodef:AlternativeIndicatorID"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="operator"
                      type="indicatorexpression-operator-type"
                      use="optional" default="and"/>
      </xs:complexType>
    </xs:element>
    <xs:simpleType name="indicatorexpression-operator-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="not"/>
        <xs:enumeration value="and"/>
        <xs:enumeration value="or"/>
        <xs:enumeration value="xor"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:element name="ObservableReference">
      <xs:complexType>
        <xs:attribute name="uid-ref" type="xs:IDREF" use="required"/>
      </xs:complexType>
    </xs:element>
    <xs:element name="IndicatorReference">
      <xs:complexType>
        <xs:attribute name="uid-ref" type="xs:IDREF" use="optional"/>
        <xs:attribute name="euid-ref" type="xs:string" use="optional"/>
        <xs:attribute name="version" type="xs:string" use="optional"/>
      </xs:complexType>

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    </xs:element>
    <xs:element name="AttackPhase">
      <xs:complexType>
        <xs:sequence>
          <xs:element ref="iodef:AttackPhaseID"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:URL" maxOccurs="unbounded"/>
          <xs:element ref="iodef:Description"
                      minOccurs="0" maxOccurs="unbounded"/>
          <xs:element ref="iodef:AdditionalData"
                      minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
      </xs:complexType>
    </xs:element>
    <xs:element name="AttackPhaseID" type="xs:string"/>
    <!--
     ===================================================================
     == Miscellaneous Classes                                         ==
     ===================================================================
    -->
    <xs:element name="AdditionalData" type="iodef:ExtensionType"/>
    <xs:element name="Description" type="iodef:MLStringType"/>
    <xs:element name="URL" type="xs:anyURI"/>
    <!--
     ===================================================================
     == IODEF Data Types                                              ==
     ===================================================================
    -->
    <xs:simpleType name="PositiveFloatType">
      <xs:restriction base="xs:float">
        <xs:minExclusive value="0"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:complexType name="MLStringType">
      <xs:simpleContent>
        <xs:extension base="xs:string">
          <xs:attribute name="translation-id"
                        type="xs:string" use="optional"/>
          <xs:attribute ref="xml:lang"/>
        </xs:extension>
      </xs:simpleContent>
    </xs:complexType>
    <xs:simpleType name="PortlistType">
      <xs:restriction base="xs:string">
        <xs:pattern value="\d+(\-\d+)?(,\d+(\-\d+)?)*"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="TimezoneType">

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      <xs:restriction base="xs:string">
        <xs:pattern value="Z|[\+\-](0[0-9]|1[0-4]):[0-5][0-9]"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:complexType name="ExtensionType" mixed="true">
      <xs:sequence>
        <xs:any namespace="##any" processContents="lax"
                minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>

      <xs:attribute name="name" type="xs:string" use="optional"/>
      <xs:attribute name="dtype"
                    type="iodef:dtype-type" use="required"/>
      <xs:attribute name="ext-dtype" type="xs:string" use="optional"/>
      <xs:attribute name="meaning" type="xs:string" use="optional"/>
      <xs:attribute name="formatid" type="xs:string" use="optional"/>
      <xs:attribute name="restriction"
                    type="iodef:restriction-type" use="optional"/>
      <xs:attribute name="ext-restriction"
                    type="xs:string" use="optional"/>
      <xs:attribute name="observable-id" type="xs:ID" use="optional"/>
    </xs:complexType>
    <xs:complexType name="SoftwareType">
      <xs:sequence>
        <xs:element ref="iodef:SoftwareReference" minOccurs="0"/>
        <xs:element ref="iodef:URL"
                    minOccurs="0" maxOccurs="unbounded"/>
        <xs:element ref="iodef:Description"
                    minOccurs="0" maxOccurs="unbounded"/>
      </xs:sequence>
    </xs:complexType>
    <xs:element name="SoftwareReference">
      <xs:complexType>
        <xs:sequence>
          <xs:any namespace="##any" processContents="lax"
                  minOccurs="0" maxOccurs="unbounded"/>
        </xs:sequence>
        <xs:attribute name="spec-name"
                      type="softwarereference-spec-name-type"
                      use="required"/>
        <xs:attribute name="ext-spec-name"
                      type="xs:string" use="optional"/>
        <xs:attribute name="dtype"
                      type="softwarereference-dtype-type"
                      use="optional"/>
        <xs:attribute name="ext-dtype" type="xs:string" use="optional"/>
      </xs:complexType>
    </xs:element>

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    <xs:simpleType name="softwarereference-spec-name-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="custom"/>
        <xs:enumeration value="cpe"/>
        <xs:enumeration value="swid"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="softwarereference-dtype-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="bytes"/>
        <xs:enumeration value="integer"/>
        <xs:enumeration value="real"/>
        <xs:enumeration value="string"/>
        <xs:enumeration value="xml"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <!--
     ===================================================================
     == Global attribute type declarations                            ==
     ===================================================================
    -->
    <xs:simpleType name="yes-no-unknown-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="yes"/>
        <xs:enumeration value="no"/>
        <xs:enumeration value="unknown"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="restriction-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="default"/>
        <xs:enumeration value="public"/>
        <xs:enumeration value="partner"/>
        <xs:enumeration value="need-to-know"/>
        <xs:enumeration value="private"/>
        <xs:enumeration value="white"/>
        <xs:enumeration value="green"/>
        <xs:enumeration value="amber"/>
        <xs:enumeration value="red"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="severity-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="low"/>
        <xs:enumeration value="medium"/>

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        <xs:enumeration value="high"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="duration-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="second"/>
        <xs:enumeration value="minute"/>
        <xs:enumeration value="hour"/>
        <xs:enumeration value="day"/>
        <xs:enumeration value="month"/>
        <xs:enumeration value="quarter"/>
        <xs:enumeration value="year"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="action-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="nothing"/>
        <xs:enumeration value="contact-source-site"/>
        <xs:enumeration value="contact-target-site"/>
        <xs:enumeration value="contact-sender"/>
        <xs:enumeration value="investigate"/>
        <xs:enumeration value="block-host"/>
        <xs:enumeration value="block-network"/>
        <xs:enumeration value="block-port"/>
        <xs:enumeration value="rate-limit-host"/>
        <xs:enumeration value="rate-limit-network"/>
        <xs:enumeration value="rate-limit-port"/>
        <xs:enumeration value="redirect-traffic"/>
        <xs:enumeration value="honeypot"/>
        <xs:enumeration value="upgrade-software"/>
        <xs:enumeration value="rebuild-asset"/>
        <xs:enumeration value="harden-asset"/>
        <xs:enumeration value="remediate-other"/>
        <xs:enumeration value="status-triage"/>
        <xs:enumeration value="status-new-info"/>
        <xs:enumeration value="watch-and-report"/>
        <xs:enumeration value="defined-coa"/>
        <xs:enumeration value="other"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
    <xs:simpleType name="dtype-type">
      <xs:restriction base="xs:NMTOKEN">
        <xs:enumeration value="boolean"/>
        <xs:enumeration value="byte"/>
        <xs:enumeration value="bytes"/>
        <xs:enumeration value="character"/>

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        <xs:enumeration value="date-time"/>
        <xs:enumeration value="integer"/>
        <xs:enumeration value="ntpstamp"/>
        <xs:enumeration value="portlist"/>
        <xs:enumeration value="real"/>
        <xs:enumeration value="string"/>
        <xs:enumeration value="file"/>
        <xs:enumeration value="path"/>
        <xs:enumeration value="frame"/>
        <xs:enumeration value="packet"/>
        <xs:enumeration value="ipv4-packet"/>
        <xs:enumeration value="ipv6-packet"/>
        <xs:enumeration value="url"/>
        <xs:enumeration value="csv"/>
        <xs:enumeration value="winreg"/>
        <xs:enumeration value="xml"/>
        <xs:enumeration value="ext-value"/>
      </xs:restriction>
    </xs:simpleType>
  </xs:schema>

9.  Security Considerations

   The IODEF data model itself does not directly introduce security
   issues.  Rather, it simply defines a representation for incident
   information.  As the data encoded by the IODEF might be considered
   privacy sensitive by the parties exchanging the information or by
   those described by it, care needs to be taken in ensuring the
   appropriate disclosure during both document exchange and subsequent
   processing.  The former must be handled by a messaging format, but
   the latter risk must be addressed by the systems that process, store,
   and archive IODEF documents and information derived from them.

   Executable content could be embedded into the IODEF document directly
   or through an extension.  The IODEF parser MUST handle this content
   with care to prevent unintentional automated execution.

   The contents of an IODEF document may include a request for action or
   an IODEF parser may independently have logic to take certain actions
   based on information that it finds.  For this reason, care must be
   taken by the parser to properly authenticate the recipient of the
   document and ascribe an appropriate confidence to the data prior to
   action.

   The underlying messaging format and protocol used to exchange
   instances of the IODEF MUST provide appropriate guarantees of
   confidentiality, integrity, and authenticity.  The use of a
   standardized security protocol is encouraged.  The Real-time Inter-

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   network Defense (RID) protocol [RFC6545] and its associated transport
   binding IODEF/RID over HTTP/TLS [RFC6546] provide such security.

   In order to suggest data processing and handling guidelines of the
   encoded information, the IODEF allows a document sender to convey a
   privacy policy using the restriction attribute.  The various
   instances of this attribute allow different data elements of the
   document to be covered by dissimilar policies.  While flexible, it
   must be stressed that this approach only serves as a guideline from
   the sender, as the recipient is free to ignore it.  The issue of
   enforcement is not a technical problem.

10.  IANA Considerations

   This document registers a namespace, XML schema, and a number of
   registries that map to enumerated values defined in the schema.

10.1.  Namespace and Schema

   This document uses URNs to describe an XML namespace and schema
   conforming to a registry mechanism described in [RFC3688]

   Registration for the IODEF namespace:

   o  URI: urn:ietf:params:xml:ns:iodef-2.0

   o  Registrant Contact: See the first author of the "Author's Address"
      section of this document.

   o  XML: None.  Namespace URIs do not represent an XML specification.

   Registration for the IODEF XML schema:

   o  URI: urn:ietf:params:xml:schema:iodef-2.0

   o  Registrant Contact: See the first author of the "Author's Address"
      section of this document.

   o  XML: See the "IODEF Schema" in Section 8 of this document.

10.2.  Enumerated Value Registries

   This document creates xx identically structured registries to be
   managed by IANA:

   o  Name of the parent registry: "Incident Object Description Exchange
      Format v2 (IODEF)"

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   o  URL of the registry: http://www.iana.org/assignments/iodef2

   o  Namespace format: A registry entry consists of:

      *  Value.  An enumerated value for a given IODEF attribute.

      *  Description.  A short description of the enumerated value.

      *  Reference.  An optional list of URIs to further describe the
         value.

   o  Allocation policy: Expert Review per [RFC5226]

   The registries to be created are named in the table below in the
   "Registry Name" column.  The initial values for the Value and
   Description fields of a given registry are listed in the "IV (Value)"
   and "IV (Description)" columns respectively.  The "IV (Value)" points
   to a given schema attribute or type per Section 8.  Each enumerated
   value in the schema gets a corresponding entry in a given registry.
   The "IV (Description)" points to a section in the text of this
   document.  The initial value of the Reference field of every registry
   entry described below should be this document.

   +------------------------+-------------------------+----------------+
   |     Registry Name      |        IV (Value)       |       IV       |
   |                        |                         | (Description)  |
   +------------------------+-------------------------+----------------+
   |      Restriction       |  iodef-restriction-type | Section 3.3.1  |
   |                        |                         |                |
   |    Incident-purpose    |     Incident@purpose    |  Section 3.2   |
   |                        |                         |                |
   |    Incident-status     |     Incident@status     |  Section 3.2   |
   |                        |                         |                |
   |      Contact-role      |       Contact@role      |  Section 3.9   |
   |                        |                         |                |
   |      Contact-type      |       Contact@type      |  Section 3.9   |
   |                        |                         |                |
   |    RegistryHandle-     | RegistryHandle@registry | Section 3.9.1  |
   |        registry        |                         |                |
   |                        |                         |                |
   |     Telephone-type     |      Telephone@type     | Section 3.9.4  |
   |                        |                         |                |
   |       Email-type       |        Email@type       | Section 3.9.3  |
   |                        |                         |                |
   |   Expectation-action   |    iodef:action-type    |  Section 3.15  |
   |                        |                         |                |
   |    Discovery-source    |     Discovery@source    |  Section 3.10  |
   |                        |                         |                |

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   |   SystemImpact-type    |    SystemImpact@type    | Section 3.12.1 |
   |                        |                         |                |
   |    BusinessImpact-     | BusinessImpact@severity | Section 3.12.2 |
   |        severity        |                         |                |
   |                        |                         |                |
   |  BusinessImpact-type   |   BusinessImpact@type   | Section 3.12.2 |
   |                        |                         |                |
   |   TimeImpact-metrics   |    TimeImpact@metric    | Section 3.12.3 |
   |                        |                         |                |
   |  TimeImpact-duration   |   iodef:duration-type   | Section 3.12.3 |
   |                        |                         |                |
   |   NodeRole-category    |    NodeRole@category    | Section 3.18.2 |
   |                        |                         |                |
   |    System-category     |     System@category     |  Section 3.17  |
   |                        |                         |                |
   |    System-ownership    |     System@ownership    |  Section 3.17  |
   |                        |                         |                |
   |    Address-category    |     Address@category    | Section 3.18.1 |
   |                        |                         |                |
   |      Counter-type      |       Counter@type      | Section 3.18.3 |
   |                        |                         |                |
   |      Counter-unit      |       Counter@unit      | Section 3.18.3 |
   |                        |                         |                |
   |   DomainData-system-   |    DomainData@system-   |  Section 3.19  |
   |         status         |          status         |                |
   |                        |                         |                |
   |   DomainData-domain-   |    DomainData@domain-   |  Section 3.19  |
   |         status         |          status         |                |
   |                        |                         |                |
   |   RecordPattern-type   |    RecordPattern@type   | Section 3.22.2 |
   |                        |                         |                |
   |     RecordPattern-     | RecordPattern@offsetuni | Section 3.22.2 |
   |       offsetunit       |            t            |                |
   |                        |                         |                |
   |   Key-registryaction   |    Key@registryaction   | Section 3.23.1 |
   |                        |                         |                |
   |     HashData-scope     |      HashData@scope     |  Section 3.26  |
   |                        |                         |                |
   |  BulkObservable-type   |   BulkObservable@type   |    Section     |
   |                        |                         |    3.29.3.1    |
   |                        |                         |                |
   |  IndicatorExpression-  | IndicatorExpression@ope | Section 3.29.4 |
   |        operator        |          rator          |                |
   |                        |                         |                |
   |  ExtensionType-dtype   |     iodef:dtype-type    |  Section 2.17  |
   |                        |                         |                |
   |   SoftwareReference-   | SoftwareReference@spec- | Section 2.16.1 |
   |        spec-id         |            id           |                |

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   |                        |                         |                |
   |   SoftwareReference-   | SoftwareReference@dtype | Section 2.16.1 |
   |         dtype          |                         |                |
   +------------------------+-------------------------+----------------+

                 Table 1: IANA Enumerated Value Registries

11.  Acknowledgments

   Many thanks to the MILE working group chairs, secretary, and area
   directors who provided feedback and governance to include Alexey
   Melnikov, Kathleen Moriarty, Takeshi Takahashi, Brian Trammel, Sean
   Turner and David Waltermire; Paul Stockler for his editorial
   leadership; and the individuals (listed alphabetically) who
   contributed during meetings and on the mailing list to include ...
   TODO ...

12.  References

12.1.  Normative References

   [W3C.XML]  World Wide Web Consortium, "Extensible Markup Language
              (XML) 1.0 (Second Edition)", W3C Recommendation , October
              2000, <http://www.w3.org/TR/2000/REC-xml-20001006>.

   [W3C.SCHEMA]
              World Wide Web Consortium, "XML XML Schema Part 1:
              Structures Second Edition", W3C Recommendation , October
              2004, <http://www.w3.org/TR/xmlschema-1/>.

   [W3C.SCHEMA.DTYPES]
              World Wide Web Consortium, "XML Schema Part 2: Datatypes
              Second Edition", W3C Recommendation , October 2004,
              <http://www.w3.org/TR/xmlschema-2/>.

   [W3C.XMLNS]
              World Wide Web Consortium, "Namespaces in XML", W3C
              Recommendation , January 1999,
              <http://www.w3.org/TR/REC-xml-names/>.

   [W3C.XPATH]
              World Wide Web Consortium, "XML Path Language (XPath)
              2.0", W3C Candidate Recommendation , June 2006,
              <http://www.w3.org/TR/xpath20/>.

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   [W3C.XMLSIG]
              World Wide Web Consortium, "XML Signature Syntax and
              Processing 2.0", W3C Candidate Recommendation , June 2008,
              <http://www.w3.org/TR/xmldsig-core/>.

   [IEEE.POSIX]
              Institute of Electrical and Electronics Engineers,
              "Information Technology - Portable Operating System
              Interface (POSIX) - Part 1: Base Definitions",
              IEEE 1003.1, June 2001.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", RFC 2119, March 1997.

   [RFC5646]  Philips, A. and M. Davis, "Tags for Identifying of
              Languages", RFC 5646, September 2009.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifiers (URI): Generic Syntax", RFC 3986,
              January 2005`.

   [RFC2978]  Freed, N. and J. Postel, "IANA Charset Registration
              Procedures", BCP 2978, October 2000.

   [RFC4519]  Sciberras, A., "Schema for User Applications", RFC 4519,
              June 2006.

   [RFC5322]  Resnick, P., "Internet Message Format", RFC 5322, October
              2008.

   [RFC3339]  Klyne, G. and C. Newman, "Date and Time on the Internet:
              Timestamps", RFC 3339, July 2002.

   [RFC-ENUM]
              Montville, A. and D. Black, "IODEF Enumeration Reference
              Format", RFC ENUM, January 2015.

   [RFC-SCI]  Takahashi, T., Landfield, K., and Y. Kadobayashi, "An
              Incident Object Description Exchange Format (IODEF)
              Extension for Structured Cybersecurity Information",
              RFC 5901, April 2014.

   [ISO8601]  International Organization for Standardization,
              "International Standard: Data elements and interchange
              formats - Information interchange - Representation of
              dates and times", ISO 8601, Second Edition, December 2000.

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   [ISO4217]  International Organization for Standardization,
              "International Standard: Codes for the representation of
              currencies and funds, ISO 4217:2001", ISO 4217:2001,
              August 2001.

   [RFC3688]  Mealling, M., "The IETF XML Registry", RFC 3688, January
              2004.

   [IANA.Ports]
              Internet Assigned Numbers Authority, "Service Name and
              Transport Protocol Port Number Registry", January 2014,
              <http://www.iana.org/assignments/service-names-port-
              numbers/service-names-port-numbers.txt>.

   [IANA.Protocols]
              Internet Assigned Numbers Authority, "Assigned Internet
              Protocol Numbers", January 2014,
              <http://www.iana.org/assignments/protocol-numbers/
              protocol-numbers.txt>.

   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", RFC 3629, November 2003.

   [RFC2781]  Hoffman, P. and F. Yergeau, "UTF-16, an encoding of ISO
              10646", RFC 2781, February 2000.

   [IANA.Media]
              Internet Assigned Numbers Authority, "Media Types", March
              2015, <http://www.iana.org/assignments/media-types/
              media-types.xhtml>.

12.2.  Informative References

   [RFC5070]  Danyliw, R., Meijer, J., and Y. Demchenko, "Incident
              Object Description Exchange Format", RFC 5070, December
              2007.

   [refs.requirements]
              Keeni, G., Demchenko, Y., and R. Danyliw, "Requirements
              for the Format for Incident Information Exchange (FINE)",
              Work in Progress, June 2006.

   [RFC4765]  Debar, H., Curry, D., Debar, H., and B. Feinstein,
              "Intrusion Detection Message Exchange Format", RFC 4765,
              March 2007.

   [RFC6545]  Moriarty, K., "Real-time Inter-network Defense (RID)",
              RFC 6545, April 2012.

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   [RFC6546]  Trammell, B., "Transport of Real-time Inter-network
              Defense (RID) Messages over HTTP/TLS", RFC 6546, April
              2012.

   [RFC5901]  Cain, P. and D. Jevans, "Extensions to the IODEF-Document
              Class for Reporting Phishing", RFC 5901, July 2010.

   [NIST800.61rev2]
              Cichonski, P., Millar, T., Grance, T., and K. Scarfone,
              "NIST Special Publication 800-61 Revision 2: Computer
              Security Incident Handling Guide", January 2012,
              <http://csrc.nist.gov/publications/nistpubs/800-61rev2/
              SP800-61rev2.pdf>.

   [RFC3982]  Newton, A. and M. Sanz, "IRIS: A Domain Registry (dreg)
              Type for the Internet Registry Information Service
              (IRIS)", RFC 3982, January 2005.

   [KB310516]
              Microsoft Corporation, "How to add, modify, or delete
              registry subkeys and values by using a registration
              entries (.reg) file", December 2007.

   [RFC4180]  Shafranovich, Y., "Common Format and MIME Type for Comma-
              Separated Values (CSV) File", RFC 4180, October 2005.

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", RFC 5226, May 2008.

Author's Address

   Roman Danyliw
   CERT - Carnegie Mellon University
   Pittsburgh, PA
   USA

   EMail: rdd@cert.org

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