SAML Profile for the Metadata Query Protocol
draft-young-md-query-saml-16
| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Ian Young | ||
| Last updated | 2022-01-10 | ||
| Stream | (None) | ||
| Intended RFC status | (None) | ||
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| Stream | Stream state | (No stream defined) | |
| Consensus boilerplate | Unknown | ||
| RFC Editor Note | (None) | ||
| IESG | IESG state | I-D Exists | |
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| Send notices to | (None) |
draft-young-md-query-saml-16
Network Working Group I.A. Young, Ed.
Internet-Draft Independent
Intended status: Informational 10 January 2022
Expires: 14 July 2022
SAML Profile for the Metadata Query Protocol
draft-young-md-query-saml-16
Abstract
This document profiles the Metadata Query Protocol for use with SAML
metadata.
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.17.
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 https://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."
This Internet-Draft will expire on 14 July 2022.
Copyright Notice
Copyright (c) 2022 IETF Trust and the persons identified as the
document authors. All rights reserved.
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This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://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 . . . . . . . . . . . . . . . . . . 4
2.2.2. Transformed Identifier . . . . . . . . . . . . . . . 4
2.2.3. Additional Identifiers . . . . . . . . . . . . . . . 5
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 . . . . . . . . . . . . . . . . . . . . . . . . 6
4.2. Use of SHA-1 in Transformed Identifiers . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
7.1. Normative References . . . . . . . . . . . . . . . . . . 7
7.2. Informative References . . . . . . . . . . . . . . . . . 8
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 . . . . . . . . . . . 10
A.8. Since draft-young-md-query-saml-06 . . . . . . . . . . . 10
A.9. Since draft-young-md-query-saml-07 . . . . . . . . . . . 10
A.10. Since draft-young-md-query-saml-08 . . . . . . . . . . . 10
A.11. Since draft-young-md-query-saml-09 . . . . . . . . . . . 10
A.12. Since draft-young-md-query-saml-10 . . . . . . . . . . . 10
A.13. Since draft-young-md-query-saml-11 . . . . . . . . . . . 10
A.14. Since draft-young-md-query-saml-12 . . . . . . . . . . . 11
A.15. Since draft-young-md-query-saml-13 . . . . . . . . . . . 11
A.16. Since draft-young-md-query-saml-14 . . . . . . . . . . . 11
A.17. Since draft-young-md-query-saml-15 . . . . . . . . . . . 11
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Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 11
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", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
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
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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.
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.
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2.2.3. Additional Identifiers
Entities MAY also be associated with any number of additional
responder-defined identifiers naming arbitrary groups of entities.
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
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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.
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:
* SHOULD use an RSA keypair whose modulus is no less than 2048 bits
in length.
* MUST NOT use the SHA-1 cryptographic hash algorithm as a digest
algorithm.
* MUST NOT use the MD5 cryptographic hash algorithm as a digest
algorithm.
* 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 an 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.
The use of SHA-1 in section 3.6.4 of [SAML2Bind], and its resulting
use in this protocol, would be vulnerable to an attack in which
metadata was introduced into a system by an attacker capable of
creating an entity identifier with the same SHA-1 hash as that of an
existing entity's identifier.
Such an identifier is known as a _second preimage_ of the original,
and SHA-1's resistance to discovery of it is referred to as SHA-1's
_second-preimage resistance_.
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As demonstrated by the the [SHAttered] and [Shambles] attacks, the
SHA-1 algorithm is known to have weak collision resistance. However,
at the time of writing no attacks are known on SHA-1's second-
preimage resistance; a result in this area would be required to
provide the basis of an attack based on duplicating the SHA-1 hash of
an existing identifier. As a result, the use of SHA-1 in SAML and in
this protocol is not believed to introduce a security concern.
Implementations may guard against the possibility of a future
practical attack on the second-preimage resistance of SHA-1 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)
Leif Johansson (SUNET)
Joe St Sauver (University of Oregon)
Tom Scavo (Internet2)
7. References
7.1. Normative References
[I-D.young-md-query]
Young, I.A., Ed., "Metadata Query Protocol", Work in
Progress, Internet-Draft, draft-young-md-query-16, January
2022, <https://datatracker.ietf.org/doc/html/draft-young-
md-query-16>.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[RFC3174] Eastlake 3rd, D. and P. Jones, "US Secure Hash Algorithm 1
(SHA1)", RFC 3174, DOI 10.17487/RFC3174, September 2001,
<https://www.rfc-editor.org/info/rfc3174>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[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, <http://docs.oasis-open.org/security/saml/v2.0/saml-
metadata-2.0-os.pdf>.
[STD68] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", STD 68, RFC 5234,
DOI 10.17487/RFC5234, January 2008,
<https://www.rfc-editor.org/info/rfc5234>.
7.2. Informative References
[md-query] Young, I.A., Ed., "md-query Project",
<https://github.com/iay/md-query>.
[MDX.list] Young, I.A., 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/>.
[REFEDS.agreement]
Research and Education Federations, "REFEDS Participant's
Agreement",
<https://refeds.org/about/about_agreement.html>.
[RFC4844] Daigle, L., Ed. and Internet Architecture Board, "The RFC
Series and RFC Editor", RFC 4844, DOI 10.17487/RFC4844,
July 2007, <https://www.rfc-editor.org/info/rfc4844>.
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[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>.
[Shambles] "SHA-1 is a Shambles", January 2020,
<https://sha-mbles.github.io>.
[SHAttered]
"SHAttered", February 2017, <https://shattered.io>.
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].
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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].
A.9. Since draft-young-md-query-saml-07
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
A.10. Since draft-young-md-query-saml-08
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
Modernise normative language to include [RFC8174].
Improved references to RFCs.
A.11. Since draft-young-md-query-saml-09
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
A.12. Since draft-young-md-query-saml-10
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
Replace citations in the abstract with straight textual mentions, as
required by the ID-NITS checklist.
A.13. Since draft-young-md-query-saml-11
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
Strengthen Section 4.1 so that SHA-1 now MUST NOT be used in the
context of digital signatures. This brings the section in line with
current best practice recommendations, particularly in light of the
[SHAttered] and [Shambles] attacks.
Revised Section 4.2 on the use of SHA-1 in transformed identifiers
to:
* Make clear that this is a SAML-level issue, not one introduced by
the query protocol.
* Reference the attacks demonstrating SHA-1's weak collision
resistance.
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* Identify second-preimage resistance as the potential source of the
attack we'd be concerned about for the query protocol.
* Note that SHA-1's second-preimage resistance is at present
uncompromised.
A.14. Since draft-young-md-query-saml-12
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
A.15. Since draft-young-md-query-saml-13
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
A.16. Since draft-young-md-query-saml-14
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
A.17. Since draft-young-md-query-saml-15
Bump reference to the Metadata Query Protocol [I-D.young-md-query].
Author's Address
Ian A. Young (editor)
Independent
Email: ian@iay.org.uk
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