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KITTEN WG                                                    N. Williams
Internet-Draft                                                       Sun
Expires: December August 28, 2006                                 June 26, 2006 2008                               February 25, 2008


  Clarifications and Extensions to the GSS-API for the Use of Channel
                                Bindings
            draft-ietf-kitten-gssapi-channel-bindings-02.txt
            draft-ietf-kitten-gssapi-channel-bindings-03.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006). IETF Trust (2008).














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Abstract

   This document clarifies and generalizes the GSS-API Generic Security Services
   Application Programming Interface (GSS-API) "channel bindings" facility.  This document also specifies the format
   facility, and imposes requirements on future GSS-API mechanisms and
   programming language bindings of the
   various types of channel bindings.








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Table of Contents

   1.  Conventions used in this document . . . . . . . . . . . . . . . 3
   2.  Introduction . . . . . . . . . . . . .  New Requirements for GSS-API Mechanisms . . . . . . . . . . . . 4
   3.  Generic Structure for GSS-API Channel Bindings  . . . . . . . . 5
     3.1.  Proper Mechanism Use of Channel Bindings . . . . . . . . .  5
   4.  Channel Bindings for SSHv2 . . . . . . . . . .  Security Considerations . . . . . . . .  6
     4.1.  GSS_Make_sshv2_channel_bindings() . . . . . . . . . . . . 6
       4.1.1.  C-Bindings .
   5.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   5.  Channel Bindings for TLS . . . . . . .
   Author's Address  . . . . . . . . . . . .  8
     5.1.  GSS_Make_tls_channel_bindings() . . . . . . . . . . . . . 8
       5.1.1.  C-Bindings . . . . . . . . . . . .
   Intellectual Property and Copyright Statements  . . . . . . . . . . 9
   6.


































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1.  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].














































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2.  New Requirements for IPsec . . . . . . . . . . . . . . . . . . 10
     6.1.  GSS_Make_ipsec_channel_bindings()  . . . . . . . . . . . . 10
       6.1.1.  C-Bindings . . . . . . . . . . . . . . . . . . . . . . 11
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 12
   8.  Normative  . . . . . . . . . . . . . . . . . . . . . . . . . . 12
   Appendix A.  Acknowledgments . . . . . . . . . . . . . . . . . . . 13
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 14
   Intellectual Property and Copyright Statements . . . . . . . . . . 15































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1.  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].














































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2.  Introduction

   The concept of "channel bindings" and Mechanisms

   Given the abstract construction publication of
   channel bindings for several types of channels are described in
   [I-D.ietf-nfsv4-channel-bindings]

   To actually use channel bindings in GSS-API aplications additional
   details are required RFC5056 we now assert that are given below.

   First the structure given to channel bindings data in [RFC2744] is
   generalized to all of the GSS-API, not just its C-Bindings.

   Then the actual construction of new GSS-API
   mechanisms that support channel bindings binding MUST conform to SSHv2, TLS and
   IPsec channels is given. [RFC5056].















































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3.  Generic Structure for GSS-API Channel Bindings

   The base GSS-API v2, update 1 specification [RFC2743]describes [RFC2743] provides a
   facility for channel binding.  It models channel bindings as an OCTET
   STRING and leaves it to the GSS-API v2, update 1 C-Bindings
   specification to specify the structure of the contents of the channel
   bindings OCTET STRINGs.  The C-Bindings specification [RFC2744]then
   defines, in terms of C, what should be have been a generic structure for
   channel bindings.  The Kerberos V GSS mechanism [RFC1964]then defines
   a method for encoding GSS channel bindings in a way that is
   independent of the C-Bindings! C-Bindings -- otherwise the mechanism's channel
   binding facility would not be useable with other language bindings.

   In other words, the structure of GSS channel bindings given in
   [RFC2744] is actually generic, rather than specific to the C
   programming language.

   Here, then, is a generic re-statement of this structure, in pseudo-
   ASN.1:

                   GSS-CHANNEL-BINDINGS := SEQUENCE {
                           initiator-address-type        INTEGER,
                           initiator-address        OCTET STRING,
                           acceptor-address-type   INTEGER,
                           acceptor-address        OCTET STRING,
                           application-data        OCTET STRING,
                   }

   The values for the address fields are described in [RFC2744].

   Language-specific

   New language-specific bindings of the GSS-API should SHOULD specify a language-
   specific
   language-specific formulation of this structure.

3.1.  Proper Mechanism Use of Channel Bindings

   As described in [I-D.ietf-nfsv4-channel-bindings], GSS mechanisms
   should exchange integrity protected proofs of channel bindings, where
   the proof is obtained by running

   Where a strong hash language binding of the GSS-API models channel bindings data (encoded as per some mechanism-specific, such as in
   [RFC1964]) and a binary value to represent
   OCTET STRINGs (or the initiator->acceptor,
   and opposite, direction.

   The encoding of channel language's equivalent), then the implementation
   MUST assume that the given bindings used in [RFC1964], with correspond only to the addition
   application-data field of a binary value GSS-CHANNEL-BINDINGS as described shown above, and the substitution of
   stronger hash functions (or even the identity function) for MD5 is a
   reasonable, generic rather
   than some encoding of GSS-CHANNEL-BINDINGS that any future
   GSS GSS-CHANNEL-BINDINGS.

   GSS-API mechanisms can use. MAY use the [RFC1964] encoding of channel
   bindings.










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4.  Channel Bindings for SSHv2

   The SSHv2 channel bindings are constructed as an octet string for the
   'application-data' field of the channel bindings by concatenating the
   following values and in this order:

   1.  The ASCII string "GSS SSHv2 CB:"

   2.  Four octet network byte order length of the SSHv2 session ID

   3.  The SSHv2 session ID           February 2008


4.  Any additional application-provided data, encoded as the DER
       encoding of an ASN.1 OCTET STRING

4.1.  GSS_Make_sshv2_channel_bindings()

   Inputs:


   o  session_id OCTET STRING,

   o  additional_app_data OCTET STRING

   Outputs:


   o  major_status INTEGER,

   o  minor_status INTEGER,

   o  channel_bindings_app_data OCTET STRING

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_FAILURE indicates failure  Security Considerations

   For general security considerations relating to construct the channel bindings
      as a result, perhaps, of a memory management, or similar failure.

   This function constructs an see
   [RFC5056].

   Language bindings that use OCTET STRING (or equivalent) for use as the value of the
   application-data field of the GSS-CHANNEL-BINDINGS structure
   described above.








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4.1.1.  C-Bindings

   OM_uint32 gss_make_sshv2_channel_bindings(
     OM_uint32                     *minor_status,
     const gss_buffer_t            session_id,
     const gss_buffer_t            additional_app_data,
     gss_buffer_t       channel_bindings_app_data
   );











































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5.  Channel Bindings for TLS

   The TLS channel
   bindings are constructed as an octet string for the
   'application-data' field of the channel bindings by concatenating the
   following values and in this order:

   1.  The ASCII string "GSS TLSv1.0 CB:"

   2.  The output of will not support the TLS PRF as applied to a constant octet string
       (TBD) (number use of octets also to be determined).

   3.  Any additional application-provided data, encoded network addresses as the DER
       encoding of an ASN.1 OCTET STRING

5.1.  GSS_Make_tls_channel_bindings()

   Inputs:


   o  prf_output OCTET STRING,

   o  additional_app_data OCTET STRING

   Outputs:


   o  major_status INTEGER,

   o  minor_status INTEGER,

   o  channel_bindings_app_data OCTET STRING

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_FAILURE indicates failure to construct the channel bindings
      as a result, perhaps, of a memory management, or similar failure.
   bindings.  This function constructs an OCTET STRING for use should not cause any security problems, as the value of the
   application-data field use of the GSS-CHANNEL-BINDINGS structure
   described above.









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5.1.1.  C-Bindings

   OM_uint32 gss_make_tls_channel_bindings(
     OM_uint32                     *minor_status,
     const gss_buffer_t            prf_octets,
     const gss_buffer_t            additional_app_data,
     gss_buffer_t          channel_bindings_app_data
   );











































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6.  Channel Bindings for IPsec

   The IPsec channel bindings are constructed
   network addresses as an octet string for the
   'application-data' field of the channel bindings by concatenating the
   following values and in this order:


   1.  The ASCII string "GSS IPsec CB:"

   2.  The transform ID for encryption, as a 16-bit big-endian word

   3.  The transform ID for integrity protection, as 16-bit in big-
       endian word

   4.  Length (four octet, network byte order) and value of the local
       IKE ID (may be a PUBLICKEY ID[I-D.ietf-btns-core])

   5.  Length (four octet, network byte order) and value of the peer IKE
       (may be a PUBLICKEY ID [I-D.ietf-btns-core]

   6.  Any additional application-provided data, encoded as the DER
       encoding of an ASN.1 OCTET STRING

   See also: [I-D.ietf-btns-connection-latching]

   Note that traffic selectors are is not included.  Inclusion of
   confidentiality/integrity algorithms protects against MITMs that can
   compromise weaker algorithms generally secure.
   However, it is important that policy might permit, for the same
   peers, for other traffic.

6.1.  GSS_Make_ipsec_channel_bindings()

   Inputs:


   o  encr_alg INTEGER,

   o  integ_alg INTEGER,

   o  initiator_id OCTET_STRING,

   o  acceptor_id OCTET_STRING,

   o  additional_app_data OCTET STRING

   Outputs:





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   o  major_status INTEGER,

   o  minor_status INTEGER,

   o  channel_bindings_app_data OCTET STRING

   Return major_status codes:

   o  GSS_S_COMPLETE indicates no error.

   o  GSS_S_FAILURE indicates failure to construct the "end-point channel bindings
      as a result, perhaps, of a memory management, or similar failure.

   This function constructs an OCTET STRING for use bindings" not be
   modelled as the value of the
   application-data field network addresses, otherwise such channel bindings may
   not be useable with all language bindings of the GSS-CHANNEL-BINDINGS structure
   described above.

6.1.1.  C-Bindings

   OM_uint32 gss_make_ipsec_channel_bindings(
     OM_uint32                     *minor_status,
     OM_uint32                     encr_alg,
     OM_uint32                     integ_alg,
     const gss_buffer_t            initiator_id,
     const gss_buffer_t            acceptor_id,
     const gss_buffer_t            additional_app_data,
     gss_buffer_t          channel_bindings_app_data
   ); GSS-API.







































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7.  Security Considerations

   For general security considerations relating to channel bindings see
   [I-D.ietf-nfsv4-channel-bindings]

8.  Normative

   [I-D.ietf-btns-connection-latching]
              Williams, N., "IPsec Channels: Connection Latching",
              draft-ietf-btns-connection-latching-00 (work in progress),
              February 2006.

   [I-D.ietf-btns-core]
              Williams, N., "Better-Than-Nothing-Security: An
              Unauthenticated Mode of IPsec", draft-ietf-btns-core-00
              (work in progress), February 2006.

   [I-D.ietf-nfsv4-channel-bindings]
              Williams, N., "On the Use of Channel Bindings to Secure
              Channels", draft-ietf-nfsv4-channel-bindings-03 (work in
              progress),           February 2005. 2008


5.  Normative References

   [RFC1964]  Linn, J., "The Kerberos Version 5 GSS-API Mechanism",
              RFC 1964, June 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2743]  Linn, J., "Generic Security Service Application Program
              Interface Version 2, Update 1", RFC 2743, January 2000.

   [RFC2744]  Wray, J., "Generic Security Service API Version 2 :
              C-bindings", RFC 2744, January 2000.


















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Appendix A.  Acknowledgments

   The author would like to thank Mike Eisler for his work on

   [RFC5056]  Williams, N., "On the Use of Channel Conjunction Mechanism I-D and for bringing the problem to a
   head, Sam Hartman for pointing out that channel bindings provide a
   general solution Bindings to the channel binding problem, Jeff Altman for his
   suggestion of using the TLS finished messages as the TLS channel
   bindings, Bill Sommerfeld, for his help in developing channel
   bindings for IPsec, and Radia Perlman for her most helpful comments. Secure
              Channels", RFC 5056, November 2007.



































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Author's Address

   Nicolas Williams
   Sun Microsystems
   5300 Riata Trace Ct
   Austin, TX  78727
   US

   Email: Nicolas.Williams@sun.com










































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