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+NETWORK WORKING GROUP S. Emery
+Internet-Draft Sun Microsystems
+Updates: 4121 (if approved) November 3, 2008
+Intended status: Standards Track
+Expires: May 7, 2009
+
+
+ Kerberos Version 5 GSS-API Channel Binding Hash Agility
+ draft-ietf-krb-wg-gss-cb-hash-agility-05.txt
+
+Status of this Memo
+
+ By submitting this Internet-Draft, each author represents that any
+ applicable patent or other IPR claims of which he or she is aware
+ have been or will be disclosed, and any of which he or she becomes
+ aware will be disclosed, in accordance with Section 6 of BCP 79.
+
+ Internet-Drafts are working documents of the Internet Engineering
+ Task Force (IETF), its areas, and its working groups. Note that
+ other groups may also distribute working documents as Internet-
+ Drafts.
+
+ 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."
+
+ The list of current Internet-Drafts can be accessed at
+ http://www.ietf.org/ietf/1id-abstracts.txt.
+
+ The list of Internet-Draft Shadow Directories can be accessed at
+ http://www.ietf.org/shadow.html.
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+ This Internet-Draft will expire on May 7, 2009.
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+Emery Expires May 7, 2009 [Page 1]
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+Internet-Draft Channel Binding Hash Agility November 2008
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+Abstract
+
+ Currently, channel bindings are implemented using a MD5 hash in the
+ Kerberos Version 5 Generic Security Services Application Programming
+ Interface (GSS-API) mechanism [RFC4121]. This document updates
+ RFC4121 to allow channel bindings using algorithms negotiated based
+ on Kerberos crypto framework as defined in RFC3961. In addition,
+ because this update makes use of the last extensible field in the
+ Kerberos client-server exchange message, extensions are defined to
+ allow future protocol extensions.
+
+
+Table of Contents
+
+ 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
+ 2. Conventions Used in This Document . . . . . . . . . . . . . . 4
+ 3. Channel binding hash agility . . . . . . . . . . . . . . . . . 5
+ 4. Security considerations . . . . . . . . . . . . . . . . . . . 7
+ 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
+ 6. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 9
+ 7. Normative References . . . . . . . . . . . . . . . . . . . . . 10
+ Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 11
+ Intellectual Property and Copyright Statements . . . . . . . . . . 12
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+Emery Expires May 7, 2009 [Page 2]
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+Internet-Draft Channel Binding Hash Agility November 2008
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+1. Introduction
+
+ With the recently discovered weaknesses in the MD5 hash algorithm
+ there is a need to use stronger hash algorithms. Kerberos Version 5
+ Generic Security Services Application Programming Interface (GSS-API)
+ mechanism [RFC4121] uses MD5 to calculate channel binding verifiers.
+ This document specifies an update to the mechanism that allows it to
+ create channel binding information based on negotiated algorithms.
+ This will allow deploying new algorithms incrementally without break
+ interoperability with older implementations, when new attacks arise
+ in the future.
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+Emery Expires May 7, 2009 [Page 3]
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+Internet-Draft Channel Binding Hash Agility November 2008
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+2. Conventions Used in This Document
+
+ 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].
+
+ The term "little endian order" is used for brevity to refer to the
+ least-significant-octet-first encoding, while the term "big endian
+ order" is for the most-significant-octet-first encoding.
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+Emery Expires May 7, 2009 [Page 4]
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+3. Channel binding hash agility
+
+ When generating a channel binding verifier, Bnd, a hash is computed
+ from the channel binding fields. Initiators MUST populate the Bnd
+ field in order to maintain interoperability with existing acceptors.
+ In addition, initiators MUST populate the extension field, Exts. All
+ fields before "Exts" do not change from what is described in
+ [RFC4121], they are listed for convenience. The 0x8003 GSS checksum
+ MUST have the following structure:
+
+ Octet Name Description
+ -----------------------------------------------------------------
+ 0..3 Lgth Number of octets in Bnd field; Represented
+ in little-endian order; Currently contains
+ hex value 10 00 00 00 (16).
+ 4..19 Bnd Channel binding information, as described in
+ section 4.1.1.2 [RFC4121].
+ 20..23 Flags Four-octet context-establishment flags in
+ little-endian order as described in section
+ 4.1.1.1 [RFC4121].
+ 24..25 DlgOpt The delegation option identifier (=1) in
+ little-endian order [optional]. This field
+ and the next two fields are present if and
+ only if GSS_C_DELEG_FLAG is set as described
+ in section 4.1.1.1 [RFC4121].
+ 26..27 Dlgth The length of the Deleg field in
+ little-endian order [optional].
+ 28..(n-1) Deleg KRB_CRED message (n = Dlgth + 28) [optional].
+ n..last Exts Extensions
+
+ where Exts is the concatenation of zero, one or more individual
+ extensions, each of which consists of, in order:
+
+ type -- big endian order unsigned integer, 32-bits, which
+ contains the type of extension
+ length -- big endian order unsigned integer, 32-bits, which
+ contains the length, in octets, of the extension data
+ encoded as an array of octets immediately following this
+ field
+ data -- octet string of extension information
+ in that order
+
+ If multiple extensions are present then there MUST be at most one
+ instance of a given extension type.
+
+ When channel binding is used the Exts MUST include the following
+ extension:
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+Emery Expires May 7, 2009 [Page 5]
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+ data-type 0x00000000
+
+ data-value
+
+ The output obtained by applying the Kerberos V get_mic()
+ operation [RFC3961], using the sub-session key from the
+ authenticator and key usage number 43, to the channel binding
+ data as described in [RFC4121], section 4.1.1.2 (using get_mic
+ instead of MD5).
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+ Initiators that are unwilling to use a MD5 hash of the channel
+ bindings MUST set the Bnd field to sixteen octets of hex value FF.
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+Emery Expires May 7, 2009 [Page 6]
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+4. Security considerations
+
+ Initiators do not know if the acceptor had ignored channel bindings
+ or whether it validated the MD5 hash of the channel bindings
+ [RFC4121].
+
+ Ultimately, it is up to the application whether to use channel
+ binding or not. This is dependent upon the security policy of these
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+Emery Expires May 7, 2009 [Page 7]
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+Internet-Draft Channel Binding Hash Agility November 2008
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+5. IANA Considerations
+
+ The IANA is hereby requested to create a new registry of "Kerberos V
+ GSS-API mechanism extension types" with four-field entries (type
+ number, type name, description, and normative reference) and,
+ initially, a single registration: 0x00000000, "Channel Binding MIC,"
+ "Extension for the verifier of the channel bindings," <this RFC>.
+
+ Using the guidelines for allocation as described in [RFC5226], type
+ number assignments are as follows:
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+ 0x00000000 - 0x000003FF IETF Consensus
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+ 0x00000400 - 0xFFFFF3FF Specification Required
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+ 0xFFFFF400 - 0xFFFFFFFF Private Use
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+Emery Expires May 7, 2009 [Page 8]
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+Internet-Draft Channel Binding Hash Agility November 2008
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+6. Acknowledgements
+
+ Larry Zhu helped in the review of this document overall and provided
+ the suggestions of typed-data.
+
+ Nicolas Williams and Sam Hartman suggested that the Bnd and Exts
+ fields be populated simultaneously.
+
+ Nicolas Williams and Jeffrey Hutzelman had also suggested a number
+ changes to this document.
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+Emery Expires May 7, 2009 [Page 9]
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+Internet-Draft Channel Binding Hash Agility November 2008
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+7. Normative References
+
+ [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
+ Requirement Levels", BCP 14, RFC 2119, March 1997.
+
+ [RFC3961] Raeburn, K., "Encryption and Checksum Specifications for
+ Kerberos 5", RFC 3961, February 2005.
+
+ [RFC4120] Neuman, C., Yu, T., Hartman, S., and K. Raeburn, "The
+ Kerberos Network Authentication Service (V5)", RFC 4120,
+ July 2005.
+
+ [RFC4121] Zhu, L., Jaganathan, K., and S. Hartman, "The Kerberos
+ Version 5 Generic Security Service Application Program
+ Interface (GSS-API) Mechanism: Version 2", RFC 4121,
+ July 2005.
+
+ [RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
+ IANA Considerations Section in RFCs", BCP 26, RFC 5226,
+ May 2008.
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+Emery Expires May 7, 2009 [Page 10]
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+Internet-Draft Channel Binding Hash Agility November 2008
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+Author's Address
+
+ Shawn Emery
+ Sun Microsystems
+ 500 Eldorado Blvd
+ M/S UBRM05-171
+ Broomfield, CO 80021
+ US
+
+ Email: shawn.emery@sun.com
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+Emery Expires May 7, 2009 [Page 11]
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+Internet-Draft Channel Binding Hash Agility November 2008
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+Full Copyright Statement
+
+ Copyright (C) The IETF Trust (2008).
+
+ This document is subject to the rights, licenses and restrictions
+ contained in BCP 78, and except as set forth therein, the authors
+ retain all their rights.
+
+ This document and the information contained herein are provided on an
+ "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
+ OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
+ THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
+ OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
+ THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
+ WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
+
+
+Intellectual Property
+
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+ Intellectual Property Rights or other rights that might be claimed to
+ pertain to the implementation or use of the technology described in
+ this document or the extent to which any license under such rights
+ might or might not be available; nor does it represent that it has
+ made any independent effort to identify any such rights. Information
+ on the procedures with respect to rights in RFC documents can be
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+Emery Expires May 7, 2009 [Page 12]
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