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Enumeration Reference Format for the Incident Object Description Exchange Format (IODEF)

The information below is for an old version of the document that is already published as an RFC.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7495.
Authors Adam W. Montville , David L. Black
Last updated 2018-12-20 (Latest revision 2015-01-30)
Replaces draft-montville-mile-enum-reference-format
RFC stream Internet Engineering Task Force (IETF)
Intended RFC status Proposed Standard
Additional resources Mailing list discussion
Stream WG state Submitted to IESG for Publication
Document shepherd David Waltermire
Shepherd write-up Show Last changed 2014-06-23
IESG IESG state Became RFC 7495 (Proposed Standard)
Action Holders
Consensus boilerplate Yes
Telechat date (None)
Responsible AD Kathleen Moriarty
Send notices to (None)
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack
INTERNET-DRAFT                                         Adam W. Montville
Intended Status: Standards Track                                   (CIS)
Expires: August 3, 2015                                      David Black
                                                        January 30, 2015

                  IODEF Enumeration Reference Format 


   The Incident Object Description Exchange Format (IODEF) is an XML
   data representation framework for sharing information about computer
   security incidents.  In IODEF, the Reference class provides
   references to externally specified information such as a
   vulnerability, Intrusion Detection System (IDS) alert, malware
   sample, advisory, or attack technique.  In practice, these references
   are based on external enumeration specifications that define both the
   enumeration format and the specific enumeration values, but the IODEF
   Reference class (as specified in IODEF v1 in RFC 5070) does not
   indicate how to include both of these important pieces of

   This document establishes a stand-alone data format to include both
   the external specification and specific enumeration identification
   value, and establishes an IANA registry to manage external
   enumeration specifications.  While this document does not update
   IODEF v1, this enumeration reference format is used in IODEF v2 and
   is applicable to other formats that support this class of enumeration

Status of this Memo

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

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any

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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at

   The list of Internet-Draft Shadow Directories can be accessed at

Copyright and License Notice

   Copyright (c) 2015 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
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document. Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document. Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1  Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
     1.1  Terminology . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Referencing External Enumerations  . . . . . . . . . . . . . .  3
   3  Security Considerations . . . . . . . . . . . . . . . . . . . .  6
   4  IANA Considerations . . . . . . . . . . . . . . . . . . . . . .  6
   5 The ReferenceName Schema . . . . . . . . . . . . . . . . . . . .  8
   6 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . .  9
   7  References  . . . . . . . . . . . . . . . . . . . . . . . . . .  9
     7.1  Normative References  . . . . . . . . . . . . . . . . . . .  9
     7.2  Informative References  . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10


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1  Introduction

   There is an identified need to specify a format to include relevant
   enumeration values from other data representation formats in an IODEF
   document. It is anticipated that this requirement will exist in other
   standardization efforts within several IETF Working Groups, but the
   scope of this document pertains solely to IODEF. This format is used
   in IODEF v2 [I-D.draft-ietf-mile-rfc5070-bis] which replaces the
   original IODEF v1 [IODEF] specification; this document does not
   specify use of this format in IODEF v1 [IODEF].

1.1  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2.  Referencing External Enumerations

   The need is to place enumeration identifiers and their enumeration
   format references in IODEF's Reference class.  There are several ways
   to accomplish this goal, but the most appropriate at this point is to
   require a specific structure for the ReferenceName string of the
   IODEF Reference class, and use an IANA registry to manage references
   to specific enumeration reference formats.

   Per IODEF [IODEF] the ReferenceName is of type ML_STRING.  This
   becomes problematic when specific references, especially enumeration
   formats such as Common Vulnerability Enumeration [CVE], Common
   Configuration Enumeration [CCE], Common Platform Enumeration [CPE]
   and so on, are referenced - how is an implementer to know which type
   of reference this is, and thus how to parse it? One solution,
   presented here, is to require that ReferenceName follow a particular

   Inclusion of such enumeration values, especially those related to
   security automation, is important to incident communication and
   investigation.  Typically, an enumeration identifier is simply an
   identifier with a specific format as defined by an external party. 
   Further, that enumeration identifier is itself a reference to
   specific information associated with the identifier.  Thus, the
   ReferenceName is an identifier that is formatted in a specific
   manner, and which identifies some set of associated information.

   For example, a vulnerability identifier following the CVE [CVE]
   formatting specification may be: CVE-2014-0001.  That identifier is
   formatted in a specific manner and relates to information about a

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   specific vulnerability.  Communicating the format for the identifier
   is the subject of this document.

 2.1 Reference Name Format

   The ReferenceName class provides the XML representation for
   identifying an enumeration and specifying a value from it.  A given
   enumeration is uniquely identified by the specIndex attribute.  Each
   specIndex value corresponds to an entry in the "Enumeration Reference
   Type Identifiers" IANA registry (see Section 4).  The child ID
   element represents a particular value from the corresponding
   enumeration identified by the specIndex attribute.  The format of the
   ID element is described in the IANA registry entry of the

         | ReferenceName           |
         | INTEGER specIndex       |<>----------[ ID    ]

                   Figure 1: The ReferenceName Class

   The aggregate classes that constitute ReferenceName:

        One. The identifier assigned to represent the particular
        enumeration object being referenced.

   The ReferenceName class has one attribute.

        Required.  INTEGER.  Enumeration identifier.  This value
        corresponds to an entry in the "Enumeration Reference Type
        Identifiers" IANA registry with an identical SpecIndex value.

   An example of such a reference is as follows:

         <enum:ReferenceName specIndex="1">

   Information in the IANA table (see Section 4) would include:

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      Full Name: Concept X Identifier
      SpecIndex: 1
      Version: any
      Specification URI:

 2.2 Reference Method Applicability

      While the scope of this document pertains to IODEF, any standard
      needing to reference an enumeration identified by a specially
      formatted string can use this method of providing structure after
      the standard has been published.  In effect, this method provides
      a standardized interface for enumeration formats, thus allowing a
      loose coupling between a given standard and the enumeration
      identifiers it needs to reference now and in the future.


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3  Security Considerations

      Ensuring a proper mapping of enumeration reference ID elements to
      the correct SpecIndex is important. Potential consequences of not
      mapping correctly include inaccurate information references and
      similar distribution of misinformation.

      Use of enumeration reference IDs from trusted sources are
      preferred to mitigate the risk of receiving and/or providing
      misinformation.  Trust decisions with respect to enumeration
      reference providers are beyond the scope of this document. 
      However, receiving an IODEF [IODEF] document containing an unknown
      ReferenceName (i.e. the SpecIndex does not exist in the IANA
      table) may indicate a misled or malicious source.

      This document is establishing a container for publicly available
      enumeration values to be included in an IODEF [IODEF] document,
      and it is important to note the distinction between the
      enumeration value's format and the information conveyed by the
      value itself.  While the enumeration value may hold information
      deemed to be private by relying parties, the enumeration format is
      likely not subject to privacy concerns. 

      However, if the Reference class includes an enumeration value in
      combination with other data in an IODEF [IODEF] document, the
      resulting combination could expose information. An example might
      include attack vectors or system descriptions used in a privacy-
      related incident.  As such, the reader is referred to the IODEF
      [IODEF] Security Considerations section, which explicitly covers
      protecting IODEF [IODEF] documents in transit and at rest,
      ensuring proper recipient authentication, data confidence levels,
      underlying transport security characteristics, and proper use of
      IODEF's restriction attribute.

4  IANA Considerations

      This document specifies an enumeration reference identifier
      format.  All fields, including abbreviation, are mandatory.

      This document creates the following registry for IANA to manage:

      Name of the Registry: "Security External Enumeration Registry"

      Location of Registry:

      Fields to record in the registry: 

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         Full Name: The full name of the enumeration (i.e. the
         referenced specification) as a string from the printable ASCII
         character set [RFC0020] with individual embedded spaces
         allowed. The ABNF [RFC5234] syntax for this field is:

               1*VCHAR *(SP 1*VCHAR)

         Abbreviation: An abbreviation may be an acronym - it consists
         of upper-case characters (at least two, upper-case is used to
         avoid mismatches due to case differences), as specified by this
         ABNF [RFC5234] syntax:

               ABBREVIATION = 2*UC-ALPHA      ; At least two
               UC-ALPHA = %x41-5A             ; A-Z

               Multiple registrations MAY use the same Abbreviation but
               MUST have different Versions.

         SpecIndex: This is an IANA-assigned positive integer that
         identifies the registration.  The first entry added to this
         registry uses the value 1, and this value is incremented for
         each subsequent entry added to the registry.

         Version: The version of the enumeration (i.e. the referenced
         specification) as a free-form string from the printable ASCII
         character set [RFC0020] excepting white space, i.e., from VCHAR
         as defined in [RFC5234].  Some of the characters allowed in the
         version string are escaped when that string is used in XML
         documents (e.g., '<' is represented as &lt;); the registered
         version string contains the unescaped ASCII character in all
         such cases.

         Specification URI/Reference: A list of one or more URIs
         [RFC3986] from which the registered specification can be
         obtained.  The registered specification MUST be readily and
         publicly available from that URI.  The URI SHOULD be a stable
         reference to a specific version of the specification.  URIs
         that designate the latest version of a specification (which
         changes when a new version appears) SHOULD NOT be used.

      Initial registry contents:

         Full Name: Common Vulnerabilities and Exposures

         Abbreviation: CVE

         SpecIndex: 1


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         Version: 1.0

         Specification URI/Reference:

      Allocation Policy: Specification Required [RFC5226] (which implies
      Expert Review [RFC5226]).

   The Designated Expert is expected to consult with the MILE (Managed
   Incident Lightweight Exchange) working group or its successor if any
   such WG exists (e.g., via email to the working group's mailing list).
   The Designated Expert is expected to review the request and validate
   the appropriateness of the enumeration for the attribute.  This
   review includes review of the specification associated with the

   The Designated Expert is expected to ensure that the Full Name,
   Abbreviation and Version are appropriate and that the information at
   the Specification URI is sufficient to unambiguously parse
   identifiers based on that specification. Additionally, the Designated
   Expert should prefer short Abbreviations over long ones.

   This document uses URNs to describe XML namespaces and XML schemas
   conforming to a registry mechanism described in [RFC3688].

   Registration request for the IODEF enumeration reference format

   URI  : urn:ietf:params:xml:ns:iodef-enum-1.0

   Registrant Contact  : See the "Authors' Addresses" section of this

   XML  : None.

   Registration request for the IODEF enumeration reference format XML

   URI  : urn:ietf:params:xml:schema:iodef-enum-1.0

   Registrant Contact  See the "Authors' Addresses" section of this

   XML  : See Section 5, "The ReferenceName Schema", of this document.

5 The ReferenceName Schema

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      <?xml version="1.0" encoding="UTF-8"?>
      <xs:schema attributeFormDefault="unqualified"

       ===  ReferenceName                                     ===
       <xs:element name="ReferenceName">
             <xs:element name="ID" type="xs:NCName"/>
           <xs:attribute name="specIndex"
                         type="xs:integer" use="required"/>

6 Acknowledgements

      The authors would like to thank Eric Burger for the recommendation
      to rely on XML, Roman D. Danyliw for his schema contribution and
      insight, and Tim Bray, Panos Kampanakis, Barry Leiba, Ted Lemon,
      Alexey Melnikov, Kathleen Moriarty, Takeshi Takahashi, Henry S.
      Thompson, and David Waltermire for their contributions and

7  References

7.1  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [IODEF]    Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident
              Object Description Exchange Format", RFC 5070, December

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              May 2008.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform

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              Resource Identifier (URI): Generic Syntax", STD 66,
              RFC 3986, January 2005.

   [RFC5234]  Crocker, D., Ed., and P. Overell, "Augmented BNF for
              Syntax Specifications: ABNF", STD 68, RFC 5234, January

   [RFC3688]  Mealling, M., "The IETF XML Registry", BCP 81, RFC 3688,
              January 2004.

7.2  Informative References

   [RFC0020]  Cerf, V., "ASCII format for network interchange", RFC 20,
              October 1969.

   [I-D.draft-ietf-mile-rfc5070-bis] Danyliw, R., and Stoecker, P., "The
              Incident Object Description Exchange Format v2", draft-
              ietf-mile-rfc5070-bis-10 (work in progress), November




Authors' Addresses

   Adam W. Montville


   David Black
   EMC Corporation


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