SAML Profile for the Metadata Query Protocol
draft-young-md-query-saml-07

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Network Working Group                                      I. Young, Ed.
Internet-Draft                                               Independent
Intended status: Informational                             July 17, 2017
Expires: January 18, 2018

              SAML Profile for the Metadata Query Protocol
                      draft-young-md-query-saml-07

Abstract

   This document profiles the Metadata Query Protocol
   [I-D.young-md-query] for use with SAML metadata [SAML2Meta].

   This document is a product of the Research and Education Federations
   (REFEDS) Working Group process.

Editorial Note (To be removed by RFC Editor before publication)

   Discussion of this draft takes place on the MDX mailing list
   (mdx@lists.iay.org.uk), which is accessed from [MDX.list].

   XML versions, latest edits and the issues list for this document are
   available from [md-query].

   The changes in this draft are summarized in Appendix A.8.

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
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   Internet-Drafts are draft documents valid for a maximum of six months
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   This Internet-Draft will expire on January 18, 2018.

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Copyright Notice

   Copyright (c) 2017 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
   to this document.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Notation and Conventions  . . . . . . . . . . . . . . . .   3
   2.  Request Profile . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Content Type  . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Identifiers . . . . . . . . . . . . . . . . . . . . . . .   3
       2.2.1.  Unique Identifier . . . . . . . . . . . . . . . . . .   3
       2.2.2.  Transformed Identifier  . . . . . . . . . . . . . . .   4
       2.2.3.  Additional Identifiers  . . . . . . . . . . . . . . .   4
   3.  Response Profile  . . . . . . . . . . . . . . . . . . . . . .   5
     3.1.  Response Cardinality  . . . . . . . . . . . . . . . . . .   5
       3.1.1.  No Entity Descriptors Returned  . . . . . . . . . . .   5
       3.1.2.  One Entity Descriptor Returned  . . . . . . . . . . .   5
       3.1.3.  More Than One Entity Descriptor Returned  . . . . . .   5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
     4.1.  Integrity . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.2.  Use of SHA-1 in Transformed Identifiers . . . . . . . . .   6
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   6
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   7
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   7
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Appendix A.  Change Log (to be removed by RFC Editor before
                publication) . . . . . . . . . . . . . . . . . . . .   9
     A.1.  draft-young-md-query-saml-00  . . . . . . . . . . . . . .   9
     A.2.  Since draft-young-md-query-saml-00  . . . . . . . . . . .   9
     A.3.  Since draft-young-md-query-saml-01  . . . . . . . . . . .   9
     A.4.  Since draft-young-md-query-saml-02  . . . . . . . . . . .   9
     A.5.  Since draft-young-md-query-saml-03  . . . . . . . . . . .   9
     A.6.  Since draft-young-md-query-saml-04  . . . . . . . . . . .   9
     A.7.  Since draft-young-md-query-saml-05  . . . . . . . . . . .   9
     A.8.  Since draft-young-md-query-saml-06  . . . . . . . . . . .   9
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . .   9

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1.  Introduction

   This document profiles the Metadata Query Protocol
   [I-D.young-md-query] for use with SAML metadata [SAML2Meta].

   The Research and Education Federations group ([REFEDS]) is the voice
   that articulates the mutual needs of research and education identity
   federations worldwide.  It aims to represent the requirements of
   research and education in the ever-growing space of access and
   identity management.

   From time to time REFEDS will wish to publish a document in the
   Internet RFC series.  Such documents will be published as part of the
   RFC Independent Submission Stream [RFC4844]; however the REFEDS
   working group sign-off process will have been followed for these
   documents, as described in the REFEDS Participant's Agreement
   [REFEDS.agreement].

   This document is a product of the REFEDS Working Group process.

1.1.  Notation and Conventions

   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 RFC 2119 [BCP14].

   This document makes use of the Augmented BNF metalanguage defined in
   [STD68].

2.  Request Profile

2.1.  Content Type

   Requests compliant with this profile MUST include the following HTTP
   header to indicate that the metadata returned should be SAML metadata
   (see Appendix A of [SAML2Meta]):

   Accept: application/samlmetadata+xml

2.2.  Identifiers

2.2.1.  Unique Identifier

   Each entity known to the responder MUST be associated with the unique
   identifier of the entity, corresponding to the "entityID" attribute
   of the entity's "EntityDescriptor" element in SAML metadata.

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2.2.2.  Transformed Identifier

   SAML 2.0 [SAML2Core] includes profiles based on the transfer of an
   "artifact" containing the unique identifier of a SAML entity
   transformed by means of the SHA-1 [RFC3174] hash algorithm (see
   [SAML2Bind] sections 3.6 and 3.6.4).

   In order to support use cases in which clients may be in possession
   of only such a transformed representation of a SAML entity's unique
   identifier without any way to establish the original entity
   identifier, a responder compliant with this profile MUST associate
   each entity with an identifier matching the "sha1id" production in
   the following ABNF grammar, and treat such an identifier as
   equivalent to the corresponding untransformed identifier:

   SHA1     = %x73 %x68 %x61 %x31 ; lower case "sha1"
   DIGIT    = %x30-39
   HEXDIGIT = DIGIT | %x61-66 ; lower case a-f
   sha1id   = "{" SHA1 "}" sha1hex
   sha1hex  = 40*HEXDIGIT

   In the above, the "sha1hex" component encodes the 20-octet (160-bit)
   binary SHA-1 hash value as a sequence of 40 lower case hexadecimal
   digits.

   For example, the identifier

   http://example.org/service

   transformed by means of SHA-1 hashing would become

   {sha1}11d72e8cf351eb6c75c721e838f469677ab41bdb

   Responder implementations MAY detect malformed SHA-1 transformed
   identifiers (for example where the string of characters following the
   "}" contains characters other than hexadecimal digits, or is other
   than exactly 40 characters in length) and return an HTTP status code
   of 400 ("bad request").  Alternatively, implementations MAY process
   these as normal identifiers and return an HTTP status code of 404
   ("not found") if appropriate.

2.2.3.  Additional Identifiers

   Entities MAY also be associated with any number of additional
   responder-defined identifiers naming arbitrary groups of entities.

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3.  Response Profile

3.1.  Response Cardinality

   A request may return information for any number of entities,
   including none.  Responses compliant with this profile MUST use the
   appropriate representation described below depending on the number of
   "EntityDescriptor" elements returned.

3.1.1.  No Entity Descriptors Returned

   A response which returns no "EntityDescriptor" elements MUST be
   represented by an HTTP status code of 404 ("not found").

3.1.2.  One Entity Descriptor Returned

   A response which returns a single "EntityDescriptor" element MUST use
   that element as its document element.  The responder MUST NOT make
   use of a "EntitiesDescriptor" element in this situation (see
   [SAML2Meta] section 2.3).

   Such a response MUST include the following HTTP header to indicate
   that the metadata returned is SAML metadata:

   Content-Type: application/samlmetadata+xml

3.1.3.  More Than One Entity Descriptor Returned

   A response which returns more than one "EntityDescriptor" element
   MUST consist of a document element which is an "EntitiesDescriptor"
   element, containing the returned "EntityDescriptor" elements as
   children.  Responses MUST NOT contain nested "EntitiesDescriptor"
   elements.

   Such a response MUST include the following HTTP header to indicate
   that the metadata returned is SAML metadata:

   Content-Type: application/samlmetadata+xml

4.  Security Considerations

4.1.  Integrity

   As SAML metadata contains information necessary for the secure
   operation of interacting services it is strongly RECOMMENDED that a
   mechanism for integrity checking is provided to clients.

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   It is RECOMMENDED that the integrity checking mechanism provided by a
   responder is a digital signature embedded in the returned metadata
   document, as defined by [SAML2Meta] section 3.

   Such digital signatures:

   o  SHOULD use an RSA keypair whose modulus is no less than 2048 bits
      in length.

   o  SHOULD NOT use the SHA-1 cryptographic hash algorithm as a digest
      algorithm.

   o  MUST NOT use the MD5 cryptographic hash algorithm as a digest
      algorithm.

   o  SHOULD otherwise follow current cryptographic best practices in
      algorithm selection.

4.2.  Use of SHA-1 in Transformed Identifiers

   This profile mandates the availability of a identifier synonym
   mechanism based on the SHA-1 cryptographic hash algorithm.  Although
   SHA-1 is now regarded as weak enough to exclude it from use in new
   cryptographic systems, its use in this profile is necessary for full
   support of the SAML 2.0 standard.

   Because the SHA-1 cryptographic hash is not being used within this
   profile in the context of a digital signature, it is not believed to
   introduce a security concern over and above that which already exists
   in SAML due to the possibility of a post-hash collision between
   entities whose "entityID" attributes hash to the same value.

   Implementations may guard against this possibility by treating two
   entities whose "entityID" values have the same SHA-1 equivalent as an
   indicator of malicious intent on the part of the owner of one of the
   entities.

5.  IANA Considerations

   This document has no actions for IANA.

6.  Acknowledgements

   The editor would like to acknowledge the following individuals for
   their contributions to this document:

      Scott Cantor (The Ohio State University)

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      Leif Johansson (SUNET)

      Joe St Sauver (University of Oregon)

      Tom Scavo (Internet2)

7.  References

7.1.  Normative References

   [BCP14]    Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [I-D.young-md-query]
              Young, I., Ed., "Metadata Query Protocol", draft-young-md-
              query-07 (work in progress), June 2016.

   [RFC3174]  Eastlake, D. and P. Jones, "US Secure Hash Algorithm 1
              (SHA1)", RFC 3174, September 2001.

   [SAML2Bind]
              Cantor, S., Hirsch, F., Kemp, J., Philpott, R., and E.
              Maler, "Bindings for the Security Assertion Markup
              Language (SAML) V2.0", OASIS Standard saml-bindings-
              2.0-os, March 2005.

   [SAML2Meta]
              Cantor, S., Moreh, J., Philpott, R., and E. Maler,
              "Metadata for the Security Assertion Markup Language
              (SAML) V2.0", OASIS Standard saml-metadata-2.0-os, March
              2005.

   [STD68]    Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

7.2.  Informative References

   [md-query]
              Young, I., Ed., "md-query Project",
              <https://github.com/iay/md-query>.

   [MDX.list]
              Young, I., Ed., "MDX Mailing List",
              <http://lists.iay.org.uk/listinfo.cgi/mdx-iay.org.uk>.

   [REFEDS]   Research and Education Federations, "REFEDS Home Page",
              <http://www.refeds.org/>.

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   [REFEDS.agreement]
              Research and Education Federations, "REFEDS Participant's
              Agreement", <https://refeds.org/about/
              about_agreement.html>.

   [RFC4844]  Daigle, L. and Internet Architecture Board, "The RFC
              Series and RFC Editor", RFC 4844, July 2007.

   [SAML2Core]
              Cantor, S., Kemp, J., Philpott, R., and E. Maler,
              "Assertions and Protocol for the OASIS Security Assertion
              Markup Language (SAML) V2.0", OASIS Standard saml-core-
              2.0-os, March 2005, <http://docs.oasis-
              open.org/security/saml/v2.0/saml-core-2.0-os.pdf>.

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Appendix A.  Change Log (to be removed by RFC Editor before publication)

A.1.  draft-young-md-query-saml-00

   Initial version.

A.2.  Since draft-young-md-query-saml-00

   Added REFEDS RFC stream boilerplate.

A.3.  Since draft-young-md-query-saml-01

   Bump reference to the Metadata Query Protocol [I-D.young-md-query].

   Rework Section 2.2 to make the role of transformed identifiers
   clearer.  This changes the semantics slightly (malformed transformed
   identifiers may now result in a 404 return rather than 400) but this
   gives implementers more latitude in the way that they handle the
   feature.

A.4.  Since draft-young-md-query-saml-02

   Bump reference to the Metadata Query Protocol [I-D.young-md-query].

A.5.  Since draft-young-md-query-saml-03

   Bump reference to the Metadata Query Protocol [I-D.young-md-query].

   Added an Editorial Note to help direct readers back to the
   discussion.

A.6.  Since draft-young-md-query-saml-04

   Fix reference to the Metadata Query Protocol [I-D.young-md-query].

A.7.  Since draft-young-md-query-saml-05

   Bump reference to the Metadata Query Protocol [I-D.young-md-query].

A.8.  Since draft-young-md-query-saml-06

   Bump reference to the Metadata Query Protocol [I-D.young-md-query].

Author's Address

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   Ian A. Young (editor)
   Independent

   EMail: ian@iay.org.uk

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