Network Working Group I. Young, Ed.
Internet-Draft Independent
Intended status: Informational December 29, 2013
Expires: July 2, 2014
SAML Profile for the Metadata Query Protocol
draft-young-md-query-saml-00
Abstract
This document profiles the Metadata Query Protocol
[I-D.young-md-query] for use with SAML metadata [SAML2Meta].
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Notation and Conventions . . . . . . . . . . . . . . . . 2
2. Request Profile . . . . . . . . . . . . . . . . . . . . . . . 2
2.1. Content Type . . . . . . . . . . . . . . . . . . . . . . 2
2.2. Identifiers . . . . . . . . . . . . . . . . . . . . . . . 3
3. Response Profile . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Response Cardinality . . . . . . . . . . . . . . . . . . 4
3.1.1. No Entity Descriptors Returned . . . . . . . . . . . 4
3.1.2. One Entity Descriptor Returned . . . . . . . . . . . 4
3.1.3. More Than One Entity Descriptor Returned . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
4.1. Integrity . . . . . . . . . . . . . . . . . . . . . . . . 4
4.2. Use of SHA-1 in Transformed Identifiers . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
7. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
7.1. Normative References . . . . . . . . . . . . . . . . . . 6
7.2. Informative References . . . . . . . . . . . . . . . . . 6
Appendix A. Change Log (to be removed by RFC Editor before
publication) . . . . . . . . . . . . . . . . . . . . 6
A.1. draft-young-md-query-saml-00 . . . . . . . . . . . . . . 6
1. Introduction
This document profiles the Metadata Query Protocol
[I-D.young-md-query] for use with SAML metadata [SAML2Meta].
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
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2.2. Identifiers
Each identifier in a request may be either:
o The unique identifier of an entity, corresponding to the
"entityID" attribute of the entity's "EntityDescriptor" element in
SAML metadata, or
o The responder-defined identifier of an arbitrary group of
entities.
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 accept an
extended identifier matching the "sha1id" production in the following
ABNF grammar as 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
Malformed SHA-1 transformed extended 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, MUST result in an HTTP status code of 400 ("bad request").
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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-01 (work in progress), December 2013.
[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
[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>.
Appendix A. Change Log (to be removed by RFC Editor before publication)
A.1. draft-young-md-query-saml-00
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Initial version.
Author's Address
Ian A. Young (editor)
Independent
EMail: ian@iay.org.uk
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