Resource-Oriented Lightweight Information Exchange
draft-ietf-mile-rolie-02

MILE Working Group                                              J. Field
Internet-Draft                                                   Pivotal
Intended status: Informational                               S. Banghart
Expires: December 5, 2016                                           NIST
                                                            June 3, 2016

           Resource-Oriented Lightweight Information Exchange
                        draft-ietf-mile-rolie-02

Abstract

   This document defines a resource-oriented approach to cyber security
   information sharing.  Using this approach, operators may share and
   exchange representations of cyber security incidents, attack
   indicators, software vulnerabilities, and other related information
   as Web-addressable resources.  Furthermore, consumers and other
   stakeholders may access and search this security content as needed,
   establishing a rapid and on-demand information exchange network for
   restricted internal use or public access repositories.  This
   specification builds on and extends the Atom Publishing Protocol and
   Atom Syndication Format to transport and share cyber security
   resource representations.  This document leverages the existing
   representations IODEF and RID where appropriate, and supports related
   cyber security representation standards.

Contributing to this document

   The source for this draft is being maintained in GitHub.  Suggested
   changes should be submitted as pull requests at
   <https://github.com/CISecurity/ROLIE>.  Instructions are on that page
   as well.  Editorial changes can be managed in GitHub, but any
   substantial issues need to be discussed on the MILE mailing list.

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

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   This Internet-Draft will expire on December 5, 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Background and Motivation . . . . . . . . . . . . . . . . . .   4
     3.1.  Message-oriented versus Resource-oriented Architecture  .   5
       3.1.1.  Message-oriented Architecture . . . . . . . . . . . .   5
       3.1.2.  Resource-Oriented Architecture  . . . . . . . . . . .   6
   4.  Atom Publication Protocol and Atom Syndication Format TODO  .   7
   5.  Normative Requirements TODO . . . . . . . . . . . . . . . . .   8
     5.1.  Atom Requirements . . . . . . . . . . . . . . . . . . . .   8
     5.2.  Transport Layer Security  . . . . . . . . . . . . . . . .   8
     5.3.  Archiving and Paging  . . . . . . . . . . . . . . . . . .   8
     5.4.  Expectation and Impact Classes  . . . . . . . . . . . . .   8
     5.5.  User Authentication . . . . . . . . . . . . . . . . . . .   9
     5.6.  User Authorization  . . . . . . . . . . . . . . . . . . .   9
     5.7.  Content Model . . . . . . . . . . . . . . . . . . . . . .   9
     5.8.  HTTP methods  . . . . . . . . . . . . . . . . . . . . . .  10
     5.9.  Service Discovery . . . . . . . . . . . . . . . . . . . .  11
       5.9.1.  Workspaces  . . . . . . . . . . . . . . . . . . . . .  11
       5.9.2.  Collections . . . . . . . . . . . . . . . . . . . . .  11
       5.9.3.  Service Document Security . . . . . . . . . . . . . .  11
     5.10. Category Mapping  . . . . . . . . . . . . . . . . . . . .  11
       5.10.1.  Collection Category  . . . . . . . . . . . . . . . .  12
       5.10.2.  Entry Category . . . . . . . . . . . . . . . . . . .  12
     5.11. Entry ID  . . . . . . . . . . . . . . . . . . . . . . . .  12
     5.12. Entry Content . . . . . . . . . . . . . . . . . . . . . .  13
     5.13. Link Relations  . . . . . . . . . . . . . . . . . . . . .  13
       5.13.1.  Additional Link Relation Requirements  . . . . . . .  15
     5.14. Member Entry Forward Security . . . . . . . . . . . . . .  15
     5.15. Date Mapping  . . . . . . . . . . . . . . . . . . . . . .  16

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     5.16. Search  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     5.17. / (forward slash) Resource URL  . . . . . . . . . . . . .  16
   6.  Security Considerations TODO  . . . . . . . . . . . . . . . .  17
   7.  IANA Considerations TODO  . . . . . . . . . . . . . . . . . .  19
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  19
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  19
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  20
     9.3.  URIs  . . . . . . . . . . . . . . . . . . . . . . . . . .  21
   Appendix A.  Change Tracking  . . . . . . . . . . . . . . . . . .  21
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  22

1.  Introduction

   This document defines a resource-oriented approach to cyber security
   information sharing that follows the REST (Architectural Styles and t
   he Design of Network-based Software Architectures) architectural
   style.  In this approach, cyber security resources are maintained in
   web-accessible repositories structured as Atom Syndication Format
   [RFC4287] feeds.  Representations of content are categorized and
   organized into indexed collections, which are requested by the
   consumer.  As the set of resource collections are forward facing, the
   consumer may search all available content for which they are
   authorized to view and request that which is desired.  Granular
   authentication and access controls permit only authorized consumers
   the ability to view, read, or write to a given feed.  This approach
   is in contrast to, and meant to improve on, the traditional point-to-
   point messaging system, in which consumers must request individual
   pieces of information from a server following a triggering event.
   This traditional approach creates a closed system of information
   sharing that encourages duplication of efforts and hinders automated
   cyber security systems.

   The goal of this document is to define the RESTful approach to cyber
   security communication with the intent of increasing communication
   and sharing of incident reports, vulnerability assessments, and other
   security content between producers, operators, and consumers.

   In order to exchange information as web-addressable resources, the
   resource representations leverage the existing IODEF [RFC5070] and
   RID [RFC6545] specifications and other representation standards as
   appropriate.  The transport protocol binding is specified as HTTP(S)
   with a media type of Atom+XML.  An appropriate set of link relation
   types specific to cyber security information sharing is defined.

   Coexistence with deployments that conform to existing specifications
   including RID [RFC6545] and Transport of Real-time Inter-network

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   Defense (RID) Messages over HTTP/TLS [RFC6546] is supported via
   appropriate use of HTTP status codes.

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
   [RFC5070].

3.  Background and Motivation

   It is well known that the field of threats to computer security is
   evolving ever more rapidly as time goes on.  As software increases in
   complexity, the number of vulnerabilities in our systems and networks
   increase exponentially.  Threat actors looking to exploit these
   vulnerabilities are making more frequent and more widely distributed
   attacks across a large variety of systems.  The adoption of liberal
   information sharing amongst attackers creates a window of as little
   as a few hours between the discovery of a vulnerability and attacks
   on the vulnerable system.  As the skills and knowledge required to
   identify and combat these attacks become more and more specialized,
   even a well established and secure system may find itself unable to
   quickly respond to an incident.  Effective identification of and
   response to a sophisticated attack requires open cooperation and
   collaboration between defending operators, software vendors, and even
   end-users.

   Existing approaches to cyber security information sharing are based
   upon message exchange patterns that are point-to-point, and event-
   driven.  Sometimes, information that may be useful to, and sharable
   with multiple peers is only made available to peers after they have
   specifically requested it.  Unfortunately, a sharing peer may not
   know, a priori, what information to request from another peer.
   Sending unsolicited RID reports does provide a mechanism for
   alerting, however these reports are again sent point-to-point, and
   must be reviewed for relevance and then prioritized for action by the
   recipient.  Thus, distribution of some relevant incident and
   indicator information may exhibit significant latency.

   In order to adequately combat the evolving threats, computer security
   resource producers should be enabled to share selected information
   proactively as appropriate.  Proactive sharing greatly aids knowledge
   dissemination as well as improving on response times and usability.

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   For example, a cyber security analyst would benefit by having the
   ability to search a comprehensive collection of attack indicators
   that have been published by a government agency, or by another member
   of a sharing consortium.  The representation of each indicator may
   include links to the related resources, enabling an appropriately
   authenticated and authorized analyst to freely navigate the
   information space of indicators, incidents, vulnerabilities, and
   other cyber security domain concepts, as needed.  In general, a more
   Web-centric sharing approach will enable a more dynamic and agile
   collaboration amongst a broader, and varying constituency.

   The following sections discuss additional specific technical issues
   that motivate the development of an alternative approach.

3.1.  Message-oriented versus Resource-oriented Architecture

   The existing approaches to cyber security information sharing are
   based upon message-oriented interactions.  The following paragraphs
   explore some of the architectural constraints associated with
   message-oriented interactions and consider the relative merits of an
   alternative model based on a Resource-oriented architecture for use
   in some use case scenarios.

   ROLIE specifies a resource-oriented architecture.

3.1.1.  Message-oriented Architecture

   In general, message-based integration architectures may be based upon
   either an RPC-style or a document-style binding.  The message types
   defined by RID represent an example of an RPC-style request.  This
   approach imposes implied requirements for conversational state
   management on both of the communicating RID endpoint(s).  Experience
   has shown that this state management frequently becomes the limiting
   factor with respect to the runtime scalability of an RPC-style
   architecture.

   In addition, the practical scalability of a peer-to-peer message-
   based approach will be limited by the administrative procedures
   required to manage O(N^2) trust relationships and at least O(N)
   policy groups.

   As long as the number of participating entities in an information
   sharing consortium is limited to a relatively small number of nodes
   (i.e., O(2^N), where N < 5), these scalability constraints may not
   represent a critical concern.  However, when there is a requirement
   to support a significantly larger number of participating peers, a
   different architectural approach will be required.  One alternative

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   to the message-based approach that has demonstrated scalability is
   the REST [REST] architectural style.

3.1.2.  Resource-Oriented Architecture

   Applying the REST architectural style to the problem domain of cyber
   security information sharing would take the approach of exposing
   incidents, indicators, and any other relevant types as simple Web-
   addressable resources.  By using this approach, an organization can
   more quickly and easily share relevant incident and indicator
   information with a much larger and potentially more diverse
   constituency.  A consumer may leverage virtually any available HTTP
   user agent in order to make requests of the service provider.  This
   improved ease of use could enable more rapid adoption and broader
   participation, thereby improving security for everyone.

   A key interoperability aspect of any RESTful Web service will be the
   choices regarding the available resource representations.  For
   example, clients may request that a given resource representation be
   returned as either XML or JSON.  In order to enable back-
   compatibility and interoperability with existing implementations,
   IODEF [RFC5070] is specified for this transport binding as a
   mandatory to implement (MTI) data representation for incident and
   indicator resources.  In addition to the REQUIRED representation, an
   implementation MAY support additional representations if and as
   needed such as IODEF extensions, the RID schema, or other schemas.
   For example, an implementation may choose to provide support for
   returning a JSON representation of an incident resource.

   Finally, an important principle of the REST architectural style is
   the use of hypertext links as the embodiment of application state
   (HATEOAS).  Rather than the server maintaining conversational state
   for each client context, the server will instead include a suitable
   set of hyperlinks in the resource representation that is returned to
   the client.  In this way, the server remains stateless with respect
   to a series of client requests.  The included hyperlinks provide the
   client with a specific set of permitted state transitions.  Using
   these links the client may perform an operation, such as updating or
   deleting the resource representation.  The client may also be
   provided with hypertext links that can be used to navigate to any
   related resource.  For example, the resource representation for an
   incident object may contain links to the related indicator
   resource(s).

   This document specifies the use of Atom Syndication Format [RFC4287]
   and Atom Publishing Protocol [RFC5023] as the mechanism for
   representing the required hypertext links.

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3.1.2.1.  A Resource-Oriented Use Case: "Mashup"

   In this section we consider a non-normative example use case scenario
   for creating a cyber security "mashup".

   Any operator can authorize any or all members of the sharing
   community to quickly and easily navigate through any of the cyber
   security information that that provider is willing to share.  An
   analyst may then make HTTP(S) requests to collect vulnerability
   information known at one producer and threat actor data being made
   available from another producer.  The resulting correlations may
   yield new insights that enable a more timely and effective defensive
   response.  Of course, this report may, in turn, be made available to
   others as a new Web-addressable resource, reachable via another URL.
   By employing the RESTful Web service approach the effectiveness of
   the collaboration amongst a consortium of cyber security stakeholders
   can be greatly improved.

4.  Atom Publication Protocol and Atom Syndication Format TODO

   As described in Atom Publishing Protocol [RFC5023], an Atom Service
   Document is an XML-based document format that allows a client to
   dynamically discover the collections provided by a publisher.

   As described in Atom Syndication Format [RFC4287], Atom is an XML-
   based document format that describes lists of related information
   items known as collections, or "feeds".  Each feed document contains
   a collection of zero or more related information items called "member
   entries" or "entries".

   When applied to the problem domain of cyber security information
   sharing, an Atom feed may be used to represent any meaningful
   collection of information resources such as a set of incidents, or
   indicators.  Each entry in a feed could then represent an individual
   incident, or indicator, or some other resource, as appropriate.
   Additional feeds could be used to represent other meaningful and
   useful collections of cyber security resources.  A feed may be
   categorized, and any feed may contain information from zero or more
   categories.  The naming scheme and the semantic meaning of the terms
   used to identify an Atom category are application-defined.

   This document assumes that the reader has an understanding of both
   Atom documents.  Further discussion of Atom's application to this
   domain a well of examples of its use are provided in the BCG
   document.

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5.  Normative Requirements TODO

   This section provides the NORMATIVE requirements for using Atom
   format and Atom Pub as a RESTful binding for cyber security
   information sharing.

5.1.  Atom Requirements

   Implementations of this specification MUST implement all requirements
   specified in Atom Publishing Protocol and the Atom Syndication
   Format.  (TODO: work on a more normative and perhaps constrained
   requirement.)

5.2.  Transport Layer Security

   Implementations MUST support server-authenticated TLS.

   Implementations MAY support mutually authenticated TLS.

5.3.  Archiving and Paging

   A feed can contain an arbitrary number of entries.  In some cases,
   the complete response to a given query may consist of a logical
   result set that contains a large number of entries.  As a practical
   matter, the full result set will likely need to be divided into more
   manageable portions.  For example, a query may produce a full result
   set that may need to be grouped into logical pages, for purposes of
   rendering on a user interface.

   An historical feed may need to be stable, and/or divided into some
   defined epochs.  Implementations SHOULD support the mechanisms
   described in Feed Paging and Archiving [RFC5005] to provide
   capabilities for paging and archiving of feeds.

5.4.  Expectation and Impact Classes

   It is frequently the case that an organization will need to triage
   their investigation and response activities based upon, e.g., the
   state of the current threat environment, or simply as a result of
   having limited resources.

   In order to enable operators to effectively prioritize their response
   activity, it is RECOMMENDED that feed implementers provide Atom
   categories that correspond to the IODEF Expectation and Impact
   classes.  The availability of these feed categories will enable
   clients to more easily retrieve and prioritize cyber security
   information that has already been identified as having a specific
   potential impact, or having a specific expectation.

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   Support for these categories may also enable efficiencies for
   organizations that already have established (or plan to establish)
   operational processes and workflows that are based on these IODEF
   classes.

5.5.  User Authentication

   Implementations MUST support user authentication.  User
   authentication MAY be enabled for specific feeds.

   Implementations MAY support more than one client authentication
   method.

   Servers participating in an information sharing consortium and
   supporting interactive user logins by members of the consortium
   SHOULD support client authentication via a federated identity scheme
   as per SAML 2.0.

   Implementations MAY support client authenticated TLS.

5.6.  User Authorization

   This document does not mandate the use of any specific user
   authorization mechanisms.  However, service implementers SHOULD
   provide appropriate authorization checking for all resource accesses,
   including individual Atom Entries, Atom Feeds, and Atom Service
   Documents.

   Authorization for a resource MAY be adjudicated based on the value(s)
   of the associated Atom <category> element(s).

   When the content model for the Atom <content> element of an Atom
   Entry contains an <IODEF-Document>, then authorization MUST be
   adjudicated based upon the Atom <category> element(s), whose values
   have been mapped as per Section 5.10.

   Any use of the <category> element(s) as an input to an authorization
   policy decision MUST include both the "scheme" and "term" attributes
   contained therein.  As described in Section 5.10 below, the namespace
   of the "term" attribute is scoped by the associated "scheme"
   attribute.

5.7.  Content Model

   Member entry resources providing a representation of an incident
   resource (e.g., as specified in the link relation type) MUST use the
   IODEF schema as the content model for the Atom Entry <content>
   element.

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   Member Entry resources providing a representation of an indicator
   resource (e.g., as specified in the link relation type) MUST use the
   IODEF schema as the content model for the Atom Entry <content>
   element.

   The resource representation MAY include an appropriate indicator
   schema type within the <AdditionalData> element of the IODEF Incident
   class.  Supported indicator schema types SHALL be registered via an
   IANA table (todo: IANA registration/review).

   Member Entry resources providing a representation of a RID report
   resource (e.g., as specified in the link relation type) MUST use the
   RID schema as the content model for the Atom Entry <content> element.

   Member Entry resources providing representation of other types,
   SHOULD use the schema appropriate for their data category as the
   content model for the Atom Entry <content> element.  These data
   categories SHALL be registered via an IANA table.

   The <content> element of the Atom entry MUST contain an appropriate
   XML namespace declaration.

5.8.  HTTP methods

   The following table defines the HTTP [RFC7235] uniform interface
   methods supported by this specification:

   +--------+----------------------------------------------------------+
   | HTTP   | Description                                              |
   | method |                                                          |
   +--------+----------------------------------------------------------+
   | GET    | Returns a representation of an individual member entry   |
   |        | resource, or a feed collection.                          |
   | PUT    | Replaces the current representation of the specified     |
   |        | member entry resource with the representation provided   |
   |        | in the HTTP request body.                                |
   | POST   | Creates a new instance of a member entry resource. The   |
   |        | representation of the new resource is provided in the    |
   |        | HTTP request body.                                       |
   | DELETE | Removes the indicated member entry resource, or feed     |
   |        | collection.                                              |
   | HEAD   | Returns metadata about the member entry resource, or     |
   |        | feed collection, contained in HTTP response headers.     |
   | PATCH  | Support TBD.                                             |
   +--------+----------------------------------------------------------+

       Table 1: Uniform Interface for Resource-Oriented Lightweight
                            Indicator Exchange

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   Clients MUST be capable of recognizing and prepared to process any
   standard HTTP status code, as defined in [RFC7235]

5.9.  Service Discovery

   This specification requires that a implementation MUST publish an
   Atom Service Document that describes the set of cyber security
   information sharing feeds that are provided.

   The service document SHOULD be discoverable via the organization's
   Web home page or another well-known public resource.

5.9.1.  Workspaces

   The service document MAY include multiple workspaces.  Any producer
   providing both public feeds and private consortium feeds MUST place
   these different classes of feeds into different workspaces, and
   provide appropriate descriptions and naming conventions to indicate
   the intended audience of each workspace.

5.9.2.  Collections

   An implementation MAY provide any number of collections within a
   given Workspace.  It is RECOMMENDED that each collection appear in
   only a single Workspace.  It is RECOMMENDED that at least one
   collection be provided that accepts new incident reports from users.
   At least one collection MUST provide a feed of incident information
   for which the content model for the entries uses the IODEF schema.
   The title of this collection SHOULD be "Incidents".

5.9.3.  Service Document Security

   Access to the service document MUST be protected via server-
   authenticated TLS and a server-side certificate.

   When deploying a service document for use by a closed consortium, the
   service document MAY also be digitally signed and/or encrypted, using
   XML DigSig and/or XML Encryption, respectively.

5.10.  Category Mapping

   This section defines normative requirements for mapping IODEF
   metadata to corresponding Atom category elements. (todo: decide
   between IANA registration of scheme, or use a full URI).

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5.10.1.  Collection Category

   An Atom collection MAY hold entries from one or more categories.  The
   collection category set MUST contain at least the union of all the
   member entry categories.  A collection MAY have additional category
   metadata that are unique to the collection, and not applicable to any
   individual member entry.  A collection containing IODEF incident
   content MUST contain at least two <category> elements.  One category
   MUST be specified with the value of the "scheme" attribute as
   "restriction".  One category MUST be specified with the value of the
   "scheme" attribute as "purpose".  The value of the "fixed" attribute
   for both of these category elements MUST be "yes".  When the category
   scheme="restriction", the allowable values for the "term" attribute
   are constrained as per section 3.2 of IODEF, e.g. public, need-to-
   know, private, default.  When the category scheme="purpose", the
   allowable values for the "term" attribute are constrained as per
   section 3.2 of IODEF, e.g. traceback, mitigation, reporting, other.

5.10.2.  Entry Category

   An Atom entry containing IODEF content MUST contain at least two
   <category> elements.  One category MUST be specified with the value
   of the "scheme" attribute as "restriction".  One category MUST be
   specified with the value of the "scheme" attribute as "purpose".
   When the category scheme="restriction", the value of the "term"
   attribute must be exactly one of ( public, need-to-know, private,
   default).  When the category scheme="purpose", the value of the
   "term" attribute must be exactly one of (traceback, mitigation,
   reporting, other).  When the purpose is "other"....

   Any member entry MAY have any number of additional categories.

5.11.  Entry ID

   The ID element for an Atom entry SHOULD be established via the
   concatenation of the value of the name attribute from the IODEF
   <IncidentID> element and the corresponding value of the <IncidentID>
   element.  This requirement ensures a simple and direct one-to-one
   relationship between an IODEF incident ID and a corresponding Feed
   entry ID and avoids the need for any system to maintain a persistent
   store of these identity mappings.

   (todo: Note that this implies a constraint on the IODEF document that
   is more restrictive than the current IODEF schema.  IODEF section 3.3
   requires only that the name be a STRING type.  Here we are stating
   that name must be an IRI.  Possible request to update IODEF to
   constrain, or to support a new element or attribute).

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5.12.  Entry Content

   The <content> element of an Atom <entry> SHOULD include an IODEF
   document.  The <entry> element SHOULD include an appropriate XML
   namespace declaration for the IODEF schema.  If the content model of
   the <entry> element does not follow the IODEF schema, then the
   <entry> element MUST include an appropriate XML namespace
   declaration.

   A client MAY ignore content that is not using the IODEF schema.

5.13.  Link Relations

   In addition to the standard Link Relations defined by the Atom
   specification, this specification defines the following additional
   Link Relation terms, which are introduced specifically in support of
   the Resource-Oriented Lightweight Information Exchange protocol.

   +-----------------------+-----------------------------+-------------+
   | Name                  | Description                 | Conformance |
   +-----------------------+-----------------------------+-------------+
   | service               | Provides a link to an atom  | MUST        |
   |                       | service document associated |             |
   |                       | with the collection feed.   |             |
   | search                | Provides a link to an       | MUST        |
   |                       | associated Open Search      |             |
   |                       | document that describes a   |             |
   |                       | URL template for search     |             |
   |                       | queries.                    |             |
   | history               | Provides a link to a        | MUST        |
   |                       | collection of zero or more  |             |
   |                       | historical entries that are |             |
   |                       | associated with the         |             |
   |                       | resource.                   |             |
   | incidents             | Provides a link to a        | MUST        |
   |                       | collection of zero or more  |             |
   |                       | instances of incident       |             |
   |                       | representations associated  |             |
   |                       | with the resource.          |             |
   | indicators            | Provides a link to a        | MUST        |
   |                       | collection of zero or more  |             |
   |                       | instances of cyber security |             |
   |                       | indicators that are         |             |
   |                       | associated with the         |             |
   |                       | resource.                   |             |
   | information           | Provides a link to a        | MUST        |
   |                       | collection of zero or more  |             |
   |                       | instances of cyber security |             |

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   |                       | information that is         |             |
   |                       | associated with the         |             |
   |                       | resource.                   |             |
   | evidence              | Provides a link to a        | SHOULD      |
   |                       | collection of zero or more  |             |
   |                       | resources that provides     |             |
   |                       | some proof of attribution   |             |
   |                       | for an incident. The        |             |
   |                       | evidence may or may not     |             |
   |                       | have any identified chain   |             |
   |                       | of custody.                 |             |
   | campaign              | Provides a link to a        | SHOULD      |
   |                       | collection of zero or more  |             |
   |                       | resources that provides a   |             |
   |                       | representation of the       |             |
   |                       | associated cyber attack     |             |
   |                       | campaign.                   |             |
   | attacker              | Provides a link to a        | SHOULD      |
   |                       | collection of zero or more  |             |
   |                       | resources that provides a   |             |
   |                       | representation of the       |             |
   |                       | attacker.                   |             |
   | vector                | Provides a link to a        | SHOULD      |
   |                       | collection of zero or more  |             |
   |                       | resources that provides a   |             |
   |                       | representation of the       |             |
   |                       | method used by the          |             |
   |                       | attacker.                   |             |
   | assessments           | Provides a link to a        | SHOULD      |
   |                       | collection of zero or more  |             |
   |                       | resources that represent    |             |
   |                       | the results of executing a  |             |
   |                       | benchmark.                  |             |
   | reports               | Provides a link to a        | SHOULD      |
   |                       | collection of zero or more  |             |
   |                       | resources that represent    |             |
   |                       | RID reports.                |             |
   | traceRequests         | Provides a link to a        | SHOULD      |
   |                       | collection of zero or more  |             |
   |                       | resources that represent    |             |
   |                       | RID traceRequests.          |             |
   | investigationRequests | Provides a link to a        | SHOULD      |
   |                       | collection of zero or more  |             |
   |                       | resources that represent    |             |
   |                       | RID investigationRequests.  |             |
   +-----------------------+-----------------------------+-------------+

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    Table 2: Link Relations for Resource-Oriented Lightweight Indicator
                                 Exchange

   Unless specifically registered with IANA these short names MUST be
   fully qualified via concatenation with a base-uri.  An appropriate
   base-uri could be established via agreement amongst the members of an
   information sharing consortium.  For example, the rel="indicators"
   relationship would become
   rel="http://www.example.org/rolie/incidents/relationships/
   indicators."

5.13.1.  Additional Link Relation Requirements

   An IODEF document that is carried in an Atom Entry SHOULD NOT contain
   a <relatedActivity> element.  Instead, the related activity SHOULD be
   available via a link rel=related.

   An IODEF document that is carried in an Atom Entry SHOULD NOT contain
   a <history> element.  Instead, the related history SHOULD be
   available via a link rel="history" (todo: or a fully qualified link
   rek name).  The associated href MAY leverage OpenSearch to specify
   the required query.

   An Atom Entry MAY include additional link relationships not specified
   here.  If a client encounters a link relationship of an unknown type
   the client MUST ignore the offending link and continue processing the
   remaining resource representation as if the offending link element
   did not appear.

5.14.  Member Entry Forward Security

   As described in Authorization Policy Enforcement a RESTful model for
   cyber security information sharing requires that all of the required
   security enforcement for feeds and entries MUST be enforced at the
   source system, at the point the representation of the given
   resource(s) is created.  A provider SHALL NOT return any feed content
   or member entry content for which the client identity has not been
   specifically authenticated, authorized, and audited.

   Sharing communities that have a requirement for forward message
   security (such that client systems are required to participate in
   providing message level security and/or distributed authorization
   policy enforcement), MUST use the RID schema as the content model for
   the member entry <content> element.

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5.15.  Date Mapping

   The Atom feed <updated> element MUST be populated with the current
   time at the instant the feed representation was generated.  The Atom
   entry <published> element MUST be populated with the same time value
   as the <reportTime> element from the IODEF document.

5.16.  Search

   Implementers MUST support OpenSearch 1.1 [opensearch] as the
   mechanism for describing how clients may form search requests.

   Implementers MUST provide a link with a relationship type of
   "search".  This link SHALL return an Open Search Description Document
   as defined in OpenSearch 1.1.

   Implementers MUST support an OpenSearch 1.1 compliant search URL
   template that enables a search query via Atom Category, including the
   scheme attribute and terms attribute as search parameters.

   Implementers SHOULD support search based upon the IODEF AlternativeID
   class as a search parameter.

   Implementers SHOULD support search based upon the four timestamp
   elements of the IODEF Incident class: <startTime>, <EndTime>,
   <DetectTime>, and <ReportTime>.

   Implementers MAY support additional search capabilities based upon
   any of the remaining elements of the IODEF Incident class, including
   the <Description> element.

   Collections that support use of the RID schema as a content model in
   the Atom member entry <content> element (e.g. in a report resource
   representation reachable via the "report" link relationship) MUST
   support search operations that include the RID MessageType as a
   search parameter, in addition to the aforementioned IODEF schema
   elements, as contained within the <ReportSchema> element.

   Implementers MUST fully qualify all OpenSearch URL template parameter
   names using the defined IODEF or RID XML namespaces, as appropriate.

5.17.  / (forward slash) Resource URL

   The "/" resource MAY be provided for compatibility with existing
   deployments that are using Transport of Real-time Inter-network
   Defense (RID) Messages over HTTP/TLS [RFC6546].  Consistent with
   RFC6546 errata, a client requesting a GET on "/" MUST receive an HTTP
   status code 405 Method Not Allowed.  An implementation MAY provide

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   full support for RFC6546 such that a POST to "/" containing a
   recognized RID message type just works.  Alternatively, a client
   requesting a POST to "/" MAY receive an HTTP status code 307
   Temporary Redirect.  In this case, the location header in the HTTP
   response will provide the URL of the appropriate RID endpoint, and
   the client may repeat the POST method at the indicated location.
   This resource could also leverage the new draft by reschke that
   proposes HTTP status code 308 (cf: draft-reschke-http-status-
   308-07.txt).

6.  Security Considerations TODO

   This document defines a resource-oriented approach to lightweight
   information exchange using HTTP, TLS, Atom Syndicate Format, and Atom
   Publishing Protocol.  As such, implementers must understand the
   security considerations described in those specifications.

   In addition, there are a number of additional security considerations
   that are unique to this specification.

   The approach described herein is based upon all policy enforcements
   being implemented at the point when a resource representation is
   created.  As such, producers sharing cyber security information using
   this specification must take care to authenticate their HTTP clients
   using a suitably strong user authentication mechanism.  Sharing
   communities that are exchanging information on well-known indicators
   and incidents for purposes of public education may choose to rely
   upon, e.g.  HTTP Authentication, or similar.  However, sharing
   communities that are engaged in sensitive collaborative analysis and/
   or operational response for indicators and incidents targeting high
   value information systems should adopt a suitably stronger user
   authentication solution, such as TLS client certificates, or a risk-
   based or multi-factor approach.  In general, trust in the sharing
   consortium will depend upon the members maintaining adequate user
   authentication mechanisms.

   Collaborating consortiums may benefit from the adoption of a
   federated identity solution, such as those based upon SAML-core
   [SAML-core] and SAML-bind [SAML-bind] and SAML-prof [SAML-prof] for
   Web-based authentication and cross-organizational single sign-on.
   Dependency on a trusted third party identity provider implies that
   appropriate care must be exercised to sufficiently secure the
   Identity provider.  Any attacks on the federated identity system
   would present a risk to the CISRT, as a relying party.  Potential
   mitigations include deployment of a federation-aware identity
   provider that is under the control of the information sharing
   consortium, with suitably stringent technical and management
   controls.

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   Authorization of resource representations is the responsibility of
   the source system, i.e. based on the authenticated user identity
   associated with an HTTP(S) request.  The required authorization
   policies that are to be enforced must therefore be managed by the
   security administrators of the source system.  Various authorization
   architectures would be suitable for this purpose, such as RBAC [1]
   and/or ABAC, as embodied in XACML [XACML].  In particular,
   implementers adopting XACML may benefit from the capability to
   represent their authorization policies in a standardized,
   interoperable format.

   Additional security requirements such as enforcing message-level
   security at the destination system could supplement the security
   enforcements performed at the source system, however these
   destination-provided policy enforcements are out of scope for this
   specification.  Implementers requiring this capability should
   consider leveraging, e.g. the <RIDPolicy> element in the RID schema.
   Refer to RFC6545 section 9 for more information.

   When security policies relevant to the source system are to be
   enforced at both the source and destination systems, implementers
   must take care to avoid unintended interactions of the separately
   enforced policies.  Potential risks will include unintended denial of
   service and/or unintended information leakage.  These problems may be
   mitigated by avoiding any dependence upon enforcements performed at
   the destination system.  When distributed enforcement is unavoidable,
   the usage of a standard language (e.g.  XACML) for the expression of
   authorization policies will enable the source and destination systems
   to better coordinate and align their respective policy expressions.

   Adoption of the information sharing approach described in this
   document will enable users to more easily perform correlations across
   separate, and potentially unrelated, cyber security information
   providers.  A client may succeed in assembling a data set that would
   not have been permitted within the context of the authorization
   policies of either provider when considered individually.  Thus,
   providers may face a risk of an attacker obtaining an access that
   constitutes an undetected separation of duties (SOD) violation.  It
   is important to note that this risk is not unique to this
   specification, and a similar potential for abuse exists with any
   other cyber security information sharing protocol.  However, the wide
   availability of tools for HTTP clients and Atom feed handling implies
   that the resources and technical skills required for a successful
   exploit may be less than it was previously.  This risk can be best
   mitigated through appropriate vetting of the client at account
   provisioning time.  In addition, any increase in the risk of this
   type of abuse should be offset by the corresponding increase in
   effectiveness that this specification affords to the defenders.

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   While it is a goal of this specification to enable more agile cyber
   security information sharing across a broader and varying
   constituency, there is nothing in this specification that necessarily
   requires this type of deployment.  A cyber security information
   sharing consortium may chose to adopt this specification while
   continuing to operate as a gated community with strictly limited
   membership.

7.  IANA Considerations TODO

   TODO.

8.  Acknowledgements

   The author gratefully acknowledges the valuable contributions of Tom
   Maguire, Kathleen Moriarty, and Vijayanand Bharadwaj.  These
   individuals provided detailed review comments on earlier drafts, and
   many suggestions that have helped to improve this document .

9.  References

9.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.

   [RFC7235]  Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
              Protocol (HTTP/1.1): Authentication", RFC 7235,
              DOI 10.17487/RFC7235, June 2014,
              <http://www.rfc-editor.org/info/rfc7235>.

   [RFC4287]  Nottingham, M., Ed. and R. Sayre, Ed., "The Atom
              Syndication Format", RFC 4287, DOI 10.17487/RFC4287,
              December 2005, <http://www.rfc-editor.org/info/rfc4287>.

   [RFC5005]  Nottingham, M., "Feed Paging and Archiving", RFC 5005,
              DOI 10.17487/RFC5005, September 2007,
              <http://www.rfc-editor.org/info/rfc5005>.

   [RFC5023]  Gregorio, J., Ed. and B. de hOra, Ed., "The Atom
              Publishing Protocol", RFC 5023, DOI 10.17487/RFC5023,
              October 2007, <http://www.rfc-editor.org/info/rfc5023>.

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   [RFC5070]  Danyliw, R., Meijer, J., and Y. Demchenko, "The Incident
              Object Description Exchange Format", RFC 5070,
              DOI 10.17487/RFC5070, December 2007,
              <http://www.rfc-editor.org/info/rfc5070>.

   [RFC6545]  Moriarty, K., "Real-time Inter-network Defense (RID)",
              RFC 6545, DOI 10.17487/RFC6545, April 2012,
              <http://www.rfc-editor.org/info/rfc6545>.

   [opensearch]
              Clinton, D., "OpenSearch 1.1 draft 5 specification", 2011,
              <http://www.opensearch.org/Specifications/OpenSearch/1.1>.

   [SAML-core]
              Cantor, S., Kemp, J., Philpott, R., and E. Mahler,
              "Assertions and Protocols for the OASIS Security Assertion
              Markup Language (SAML) V2.0", OASIS Standard , March 2005,
              <http://docs.oasis-open.org/security/saml/v2.0/
              saml-core-2.0-os.pdf>.

   [SAML-prof]
              Hughes, J., Cantor, S., Hodges, J., Hirsch, F., Mishra,
              P., Philpott, R., and E. Mahler, "Profiles for the OASIS
              Security Assertion Markup Language (SAML) V2.0", OASIS
              Standard , March 2005, <http://docs.oasis-
              open.org/security/saml/v2.0/saml-profiles-2.0-os.pdf>.

   [SAML-bind]
              Cantor, S., Hirsch, F., Kemp, J., Philpott, R., and E.
              Mahler, "Bindings for the OASIS Security Assertion Markup
              Language (SAML) V2.0", OASIS Standard , March 2005,
              <http://docs.oasis-open.org/security/saml/v2.0/
              saml-bindings-2.0-os.pdf>.

9.2.  Informative References

   [XACML]    Rissanen, E., "eXtensible Access Control Markup Language
              (XACML) Version 3.0", August 2010, <http://docs.oasis-
              open.org/xacml/3.0/xacml-3.0-core-spec-cs-01-en.pdf>.

   [REST]     Fielding, R., "Architectural Styles and the Design of
              Network-based Software Architectures", 2000,
              <http://www.ics.uci.edu/~fielding/pubs/dissertation/
              top.htm>.

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   [RFC6546]  Trammell, B., "Transport of Real-time Inter-network
              Defense (RID) Messages over HTTP/TLS", RFC 6546,
              DOI 10.17487/RFC6546, April 2012,
              <http://www.rfc-editor.org/info/rfc6546>.

9.3.  URIs

   [1] http://csrc.nist.gov/groups/SNS/rbac/

Appendix A.  Change Tracking

   Changes since draft-field-mile-rolie-01 version, December, 2015 to
   May 27, 2016:

   o  Spun section 4 and some related contextual information into its
      own document see TODO:Add reference

   o  Recast document into a more general use perspective.  The
      implication of CSIRTs as the defacto end-user has been removed
      where ever possible.  All of the original CSIRT based use cases
      remain completely supported by this document, it has been opened
      up to supported many other use cases.

   o  Changed the content model to broaden support of representation

   o  Edited and rewrote much of sections 1,2 and 3 in order to
      accomplish a broader scope and greater readability

   o  Removed any requirements from the Background section and, if not
      already stated, placed them in the requirements section

   o  Re-formatted the requirements section to make it clearer that it
      contains the lions-share of the requirements of the specification

   Changes made in draft-ietf-mile-rolie-01 since draft-field-mile-
   rolie-02 version, August 15, 2013 to December 2, 2015:

   o  Added section specifying the use of RFC5005 for Archive and Paging
      of feeds.  See: Section 5.3

   o  Added section describing use of atom categories that correspond to
      IODEF expectation class and impact classes.  See: Section 5.4

   o  Dropped references to adoption of a MILE-specific HTTP media type
      parameter.

   o  Updated IANA Considerations section to clarify that no IANA
      actions are required.

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Authors' Addresses

   John P. Field
   Pivotal Software, Inc.
   625 Avenue of the Americas
   New York, New York
   USA

   Phone: (646)792-5770
   Email: jfield@pivotal.io

   Stephen A. Banghart
   National Institute of Standards and Technology
   100 Bureau Drive
   Gaithersburg, Maryland
   USA

   Phone: (301)975-4288
   Email: sab3@nist.gov

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