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[sstc-saml-attribute-kerberos]

SAML V2.0 Kerberos Attribute Profile Version 1.0. 29 August 2011. OASIS Committee Specification 01.
http://docs.oasis-open.org/security/saml/Post2.0/sstc-saml-attribute-kerberos-cs01.html.

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Table of Contents

1 Introduction.................................................................................................................................... 5

1.1 Terminology............................................................................................................................. 5

1.2 Normative References.............................................................................................................. 5

1.3 Non-Normative References....................................................................................................... 5

2 SAML 2.0 Kerberos Attribute Profile................................................................................................ 6

2.1 Required Information................................................................................................................ 6

2.2 Profile Overview....................................................................................................................... 6

2.3 SAML Attribute Naming............................................................................................................ 6

2.3.1 Attribute Name Comparison............................................................................................... 6

2.4 Profile-Specific XML Attributes................................................................................................. 6

2.5 SAML Attribute Values............................................................................................................. 6

2.6 Kerberos Principal Naming....................................................................................................... 6

2.7 Attribute Definition................................................................................................................... 6

2.8 Examples................................................................................................................................ 7

3 Conformance.................................................................................................................................. 9

3.1 SAML 2.0 Kerberos Attribute Profile.......................................................................................... 9

Appendix A Acknowledgments....................................................................................................... 10

Appendix B Revision History.......................................................................................................... 11

1 Introduction

The SAML V2.0 Kerberos Attribute Profile describes a SAML attribute profile for requesting and expressing Kerberos protocol messages.

1.1 Terminology

The keywords "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this specification are to be interpreted as described in IETF RFC2119.

The term TLS as used in this specification refers to either the Secure Sockets Layer (SSL) Protocol 3.0 [SSL3] or any version of the Transport Layer Security (TLS) Protocol [RFC2246] [RFC4346] [RFC5256]. As used in this specification, the term TLS specifically does not refer to the SSL Protocol 2.0 [SSL2].

1.2 Normative References

[NonEncKrb] R. Yount. The Unencrypted Form Of Kerberos 5 KRB-CRED Message. IETF Internet-Draft, December 2010. See http://tools.ietf.org/id/draft-yount-krb-cred-clear-text-01.txt

[RFC2045] N. Freed et al. Multipurpose Internet Mail Extensions (MIME) Part One: Format of Internet Message Bodies, November 1996. See http://www.ietf.org/rfc/rfc2045.txt

[RFC2119] S. Bradner. Key words for use in RFCs to Indicate Requirement Levels. IETF RFC 2119, March 1997. http://www.ietf.org/rfc/rfc2119.txt

[RFC2246] T. Dierks, C. Allen. The TLS Protocol Version 1.0. IETF RFC 2246, January 1999. http://www.ietf.org/rfc/rfc2246.txt

[RFC4120] C. Neuman et al. The Kerberos Network Authentication Service (V5). IETF RFC 4120, July 2005. http://www.ietf.org/rfc/rfc4120.txt

[RFC4346] T. Dierks, E. Rescorla. The Transport Layer Security (TLS) Protocol Version 1.1. IETF RFC 4346, April 2006. http://www.ietf.org/rfc/rfc4346.txt

[RFC3061] M. Mealling. A URN Namespace of Object Identifiers. IETF RFC 3061, February 2001. http://www.ietf.org/rfc/rfc3061.txt

[Kerberos-XSD] J. Howlett et al., Kerberos schema. OASIS SSTC, November 2009. Document ID saml-schema-kerberos-2.0. See http://www.oasis-open.org/committees/download.php/35334/saml-schema-kerberos-2.0

[RFC5256] T. Dierks, E. Rescorla. The Transport Layer Security (TLS) Protocol Version 1.2. IETF RFC 5246, August 2008. http://www.ietf.org/rfc/rfc5246.txt

[SAML2Core] OASIS Standard, Assertions and Protocols for the OASIS Security Assertion Markup Language (SAML) V2.0. March 2005.http://docs.oasis-open.org/security/saml/v2.0/saml-core-2.0-os.pdf

[SSL3] A. Freier, P. Karlton, P. Kocher. The SSL Protocol Version 3.0. Netscape Communications Corp., November 18, 1996. http://www.mozilla.org/projects/security/pki/nss/ssl/draft302.txt

1.3 Non-Normative References

[SSL2] K. Hickman. The SSL Protocol. Netscape Communications Corp., February 9, 1995. http://www.mozilla.org/projects/security/pki/nss/ssl/draft02.html

2 SAML 2.0 Kerberos Attribute Profile

2.1 Required Information

Identification: urn:oasis:names:tc:SAML:2.0:profiles:attribute:kerberos

Contact information: security-services-comment@lists.oasis-open.org

Description: Given below.

Updates: None.

2.2 Profile Overview

This specification describes a SAML attribute profile that can be used to request and express Kerberos protocol messages. In this version of the specification, this is constrained to the Kerberos KRB-CRED message type. The mechanisms that are used to generate the Kerberos message are outside the scope of this document and are described by [RFC4120].

2.3 SAML Attribute Naming

The NameFormat XML attribute in <Attribute> elements MUST be urn:oasis:names:tc:SAML:2.0:attrname-format:uri.

2.3.1 Attribute Name Comparison

Two <Attribute> elements refer to the same SAML attribute if and only if their Name XML attribute values are equivalent in the sense of [RFC3061]. The FriendlyName attribute plays no role in the comparison.

2.4 Profile-Specific XML Attributes

No additional XML attributes are defined for use with the <Attribute> element.

2.5 SAML Attribute Values

The value of this attribute is a Kerberos message that is expressed using the <KerberosData> element defined in the XML namespace urn:oasis:names:tc:SAML:2.0:attribute:kerberos.

When comparing attribute values for equality, an attribute value which does not contain a <KerberosMessage> element MUST be considered equivalent to any other value. This rule is necessary to satisfy the equality condition stipulated in section 3.3.2.3 of [SAML2Core], in the case where the attribute is used within the <AttributeQuery> element.

2.6 Kerberos Principal Naming

The naming of Kerberos principals MUST adhere to the rules specified in section 2.1 of [RFC1964].

2.7 Attribute Definition

This profile currently defines a single multi-valued attribute named “krb-cred”.

Name: urn:oasis:names:tc:SAML:2.0:profiles:attribute:kerberos:krb-cred

An <AttributeValue> element MUST contain a single <KerberosData> element from the XML namespace urn:oasis:names:tc:SAML:2.0:attribute:kerberos. For purposes of human readability, there may also be a requirement for some applications to carry an optional string name together with the URI. The optional XML attribute FriendlyName (defined in [SAML2Core]) MAY be used for this purpose.

When used to request a Kerberos KRB-CRED message, this element MUST include a single instance of the <KerberosSname> element and MAY include at most a single instance of the <KerberosCname> element, naming the intended service and client principals respectively.

When used to express a Kerberos KRB-CRED message, this element MUST include single instances of the <KerberosSname> and <KerberosCame> elements naming the service and client principals identified in the KRB-CRED message and a single instance of the <KerberosMessage> element whose value takes the base64-encoded [RFC2045] representation of the KRB-CRED message and whose KerberosMsgType attribute MUST take a value of “KRB_CRED”.

The issuer SHOULD attempt to satisfy the client principal named by the requester, if given, but MAY use any other client principal (for example, if a local policy forbids or requires a particular client principal for a service).

The KRB-CRED message issued in a <KerberosMessage> element MUST conform to section 5.8 of [RFC4120].

The KRB-CRED message contains sensitive information related to Kerberos credentials being transferred, such as their secret session keys, client and server principal names, and validity period. Posession of this information, along with the ticket itself, would allow an attacker to impersonate the client named in the ticket. As a result, this information must be carefully safeguarded.

The definition of the KRB-CRED message in section 5.8 of [RFC4120] provides for protection of the confidentiality and integrity of the sensitive portions of the KRB-CRED message when it is passed in the context of a previous Kerberos authentication, by encrypting those portions in a key derived from the shared Kerberos session key. When the issuer and recipient of this attribute share an appropriate Kerberos authentication context, it SHOULD be used to protect the KRB-CRED message as described in [RFC4120].

However, the issuer and recipient of a SAML attribute often do not share an Kerberos authentication context. To facilitate use of this attribute in such cases, the non-encrypted form of the KRB-CRED message [NonEncKrb] may be used. When the non-encrypted form is used, the confidentiality and integrity of the message MUST be protected by alternate means such as Transport Layer Security (TLS) or the <EncryptedAttribute> element.

To facilitate interoperability, implementations of this profile MUST support sending and receiving the non-encrypted form of the KRB-CRED message, and MUST support protection of this attribute by use of the <EncryptedAttribute> element.

2.8 Examples

A SAML requester issues a request to a SAML attribute authority for a Kerberos KRB-CRED message:

<saml:Attribute

xmlns:kerberos="urn:oasis:names:tc:SAML:2.0:attribute:kerberos"

NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"

Name="urn:oasis:names:tc:SAML:2.0:profiles:attribute:kerberos:krb-cred">

<saml:AttributeValue>

<kerberos:KerberosData>

<kerberos:KerberosCname>

joe@EXAMPLE.ORG

</kerberos:KerberosCname>

<kerberos:KerberosSname>

http/www@EXAMPLE.ORG

</kerberos:KerberosSname>

</kerberos:KerberosData>

</saml:AttributeValue>

</saml:Attribute>

A SAML attribute authority returns a Kerberos KRB-CRED message:

<saml:Attribute

xmlns:kerberos="urn:oasis:names:tc:SAML:2.0:attribute:kerberos"

NameFormat="urn:oasis:names:tc:SAML:2.0:attrname-format:uri"

Name="urn:oasis:names:tc:SAML:2.0:profiles:attribute:kerberos:krb-cred"

<saml:AttributeValue>

<kerberos:KerberosData>

<kerberos:KerberosCname>

joe@EXAMPLE.ORG

</kerberos:KerberosCname>

<kerberos:KerberosSname>

http/www@EXAMPLE.ORG

</kerberos:KerberosSname>

<kerberos:KerberosMessage KerberosMsgType=”KRB_CRED”>

...base64 representation of a KRB-CRED message...

</kerberos:Message>

</kerberos:KerberosData>

</saml:AttributeValue>

</saml:Attribute>

3 Conformance

3.1 SAML 2.0 Kerberos Attribute Profile

An asserting party implementation conforms to this profile if it can produce assertions and other SAML-defined content consistent with the normative text of section 2.

A relying party implementation conforms to this profile if it can accept assertions and other SAML-defined content consistent with the normative text of section 2.

Appendix A Acknowledgments

The editor would like to acknowledge the contributions of the OASIS Security Services (SAML) Technical Committee:

• John Bradley, Individual

• Scott Cantor, Internet2

• Duane DeCouteau, Veterans Health Administration

• Christian Guenther, Nokia Siemens Networks GmbH & Co.

• Frederick Hirsch, Nokia Corporation

• Ari Kermaier, Oracle Corporation

• Nathan Klingenstein, Internet2

• Hal Lockhart, Oracle Corporation

• Paul Madsen, NTT Corporation

• Kyle Meadors, Drummond Group Inc.

• Bob Morgan, Internet2

• Thinh Nguyenphu, Nokia Siemens Networks GmbH & Co.

• Rob Philpott, EMC Corporation

• Anil Saldhana, Red Hat

• Tom Scavo, National Center for Supercomputing Applications

• Kent Spaulding, Skyworth TTG Holdings Limited

• David Staggs, Veterans Health Administration

• Emily Xu, Sun Microsystems

The editor would also like to acknowledge the following particular individuals who contributed to the development of this document:

• Russell Yount, CMU

• Jeffrey Hutzelman, CMU

• Scott Cantor, Internet2

• Nathan Klingenstein, Internet2

• Tom Scavo, National Center for Supercomputing Applications

• Jeff Hodges, PayPal

Appendix B Revision History

Document ID	Date	Committer	Comment
sstc-saml-attribute-kerberos-draft-01	7 Aug 2009	J. Howlett	Initial draft
sstc-saml-attribute-kerberos-draft-02	3 Sep 2009	J. Howlett	Response to comments
sstc-saml-attribute-kerberos-cd-01	18 Nov 2009	J. Howlett	Committee Draft 01
sstc-saml-attribute-kerberos-draft-03	24 Sep 2010	J. Howlett	Response to comments
sstc-saml-attribute-kerberos-draft-04	3 Dec 2010	J. Howlett	Response to comments