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Versions: 00 01 02 03 04 05 06 rfc5403                                  
NFSv4                                                          M. Eisler
Internet-Draft                                                    NetApp
Intended status: Standards Track                       February 24, 2008
Expires: August 27, 2008

                          RPCSEC_GSS Version 2

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Copyright Notice

   Copyright (C) The IETF Trust (2008).


   This Internet-Draft describes version 2 of the RPCSEC_GSS protocol.
   Version 2 is the same as Version 1 but adds support for channel

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",

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   document are to be interpreted as described in RFC 2119 [1].

Table of Contents

   1.  Introduction and Motivation . . . . . . . . . . . . . . . . . . 3
   2.  Channel Bindings Explained  . . . . . . . . . . . . . . . . . . 3
   3.  The RPCSEC_GSSv2 Protocol . . . . . . . . . . . . . . . . . . . 4
     3.1.  Compatibility with RPCSEC_GSSv1 . . . . . . . . . . . . . . 4
     3.2.  New Version Number  . . . . . . . . . . . . . . . . . . . . 4
     3.3.  New Procedure - RPCSEC_GSS_BIND_CHANNEL . . . . . . . . . . 5
     3.4.  New Security Service - rpc_gss_svc_channel_prot . . . . . . 6
   4.  Version Negotiation . . . . . . . . . . . . . . . . . . . . . . 6
   5.  Implementation Notes  . . . . . . . . . . . . . . . . . . . . . 6
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 7
   7.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   9.  Normative References  . . . . . . . . . . . . . . . . . . . . . 7
   Author's Address  . . . . . . . . . . . . . . . . . . . . . . . . . 7
   Intellectual Property and Copyright Statements  . . . . . . . . . . 8

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1.  Introduction and Motivation

   RPCSEC_GSS version 2 (RPCSEC_GSSv2) is the same as RPCSEC_GSS version
   1 (RPCSEC_GSSv1) except that support for channel bindings has been
   added.  The primary motivation for channel bindings is to securely
   take advantage of hardware assisted encryption that might exist at
   lower levels of the networking protocol stack, such as at the
   Internet Protocol (IP) layer in the form of IPsec.  The secondary
   motivation is that even if lower levels are not any more efficient at
   encryption than the RPCSEC_GSS layer, if encryption is occurring at
   the lower level, it can be redundant at the RPCSEC_GSS level.

   Once an RPCSEC_GSS target and initiator are mutually assured that
   they are each using the same secure, end to end channel, the overhead
   of computing message integrity codes (MICs) for authenticating and
   integrity protecting RPC requests and replies can be eliminated
   because the channel is performing the same function.  Similarly, if
   the channel also provides confidentiality, the overhead of RPCSEC_GSS
   privacy protect can also be eliminated.

2.  Channel Bindings Explained

   If a channel between two parties is secure, there must be shared
   information between the two parties.  This information might be
   secret or not.  The requirement for secrecy depends on the specifics
   of the channel.

   For example, the shared information could be the concatenation of the
   public key of the source and destination of the channel (where each
   public key has a corresponding private key).  Suppose the channel is
   not end-to-end, i.e. a man-in-the-middle (MITM) exists, and there are
   two channels, one from the initiator to the MITM, and one from the
   MITM to the target.  The MITM cannot simply force each channel to use
   the same public keys, because the public keys come from private keys,
   and the key management system for each node will surely assign unique
   or random private keys.  At most the MITM can force one end of each
   channel to use the same public key.  The MIC of public keys from the
   initiator will not be verified by the target, because at least one of
   public keys will be different.  Similarly, the MIC of the public keys
   from the target will not be verified by the initiator because at
   least one of the public keys will be different.

   A higher layer protocol using the secure channel can safely exploit
   the channel to the mutual benefit of the higher level parties if each
   higher level party can prove:

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   o  They each know the channel's shared information.

   o  The proof of the knowledge of the shared information is in fact
      being conveyed by each of the higher level parties, and not some
      other entities.

   RPCSEC_GSSv2 simply adds an optional round trip that has the
   initiator compute a GSS MIC on the channel binding's shared
   information, and sends the MIC to the target.  The target verifies
   the MIC, and in turn sends its own MIC of the shared information to
   the initiator which verifies the target's MIC.  This accomplishes
   three things.  First the initiator and target are mutually
   authenticated.  Second, the initiator and target prove they know the
   channel's shared information, and thus are using the same channel.
   Third, the first and second things are done simultaneously.

3.  The RPCSEC_GSSv2 Protocol

   The RPCSEC_GSSv2 protocol will now be explained.  The entire protocol
   is not presented.  Instead the differences between RPCSEC_GSSv2 and
   RPCSEC_GSSv1 are shown.

3.1.  Compatibility with RPCSEC_GSSv1

   The functionality of RPCSEC_GSSv1 is fully supported by RPCSEC_GSSv2.

3.2.  New Version Number

   const RPCSEC_GSS_VERS_1 = 1;
   const RPCSEC_GSS_VERS_2 = 2; /* new */

         struct rpc_gss_cred_t {
             union switch (unsigned int version) { /* version of
                                                         RPCSEC_GSS */
             case RPCSEC_GSS_VERS_1:
             case RPCSEC_GSS_VERS_2: /* new */
                 struct {
                     rpc_gss_proc_t gss_proc;  /* control procedure */
                     unsigned int seq_num;   /* sequence number */
                     rpc_gss_service_t service; /* service used */
                     opaque handle<>;       /* context handle */
                 } rpc_gss_cred_vers_1_t;

   As is apparent from the above, the RPCSEC_GSSv2 credential has the
   same format as the RPCSSEC_GSSv1 credential.  By setting the version
   field to 2, this indicates that the initiator and target support
   channel bindings.

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3.3.  New Procedure - RPCSEC_GSS_BIND_CHANNEL

           enum rpc_gss_proc_t {
                   RPCSEC_GSS_DATA = 0,
                   RPCSEC_GSS_INIT = 1,
                   RPCSEC_GSS_CONTINUE_INIT = 2,
                   RPCSEC_GSS_DESTROY = 3,
                   RPCSEC_GSS_BIND_CHANNEL = 4 /* new */

           struct rpc_gss_chan_bind_input {
                   opaque          rgcbi_chan_bindings<>;

   Once an RPCSEC_GSSv2 handle has been established over a secure
   channel, the client MAY issue RPCSEC_GSS_BIND_CHANNEL.  Targets MUST
   RPCSEC_GSS_CONTINUE_INIT requests, the NULL RPC procedure MUST be
   used.  Unlike those two requests, the arguments of the NULL procedure
   are not overloaded, because the verifier is of sufficient size for
   the purpose of RPCSEC_GSS_BIND_CHANNEL.  The gss_proc field is set to
   RPCSEC_GSS_BIND_CHANNEL.  The seq_num field is set as if gss_proc
   were set to RPCSEC_GSS_DATA.  The service field is set to
   rpc_gss_svc_none.  The handle field is set to that of an RPCSEC_GSS
   handle as returned by RPCSEC_GSS_INIT or RPCSEC_GSS_CONTINUE_INIT.

   When gss_proc is RPCSEC_GSS_DATA, the verifier of an RPC request is
   set to the output of GSS_GetMIC() on the RPC header as described in
   Section 5.3.1 of [2].  When gss_proc is RPCSEC_GSS_BIND_CHANNEL, the
   verifier of an RPC request is set to the output of GSS_GetMIC() on
   the concatenation of the RPC header ("up to and including the
   credential") and the XDR encoding of an instance of type data

   Similarly when gss_proc is RPCSEC_GSS_DATA, the verifier of an RPC
   reply is set to the output of GSS_GetMIC() on the seq_num of the
   credential of the corresponding request (as described in Section of [2]).  When gss_proc is RPCSEC_GSS_BIND_CHANNEL, the
   verifier of an RPC reply is set to the ouput of GSS_GetMIC() on the
   concantenation of the seq_num and the XDR encoding of an instance of
   data type rpc_gss_chan_bind_input.

   The content of rpc_gss_chan_bind_input has a single field,
   rgcbi_chan_bindings.  The rgcbi_chan_bindings field consists of
   channel bindings as defined in [3].  The channel bindings are a
   "canonical octet string encoding of the channel bindings", starting
   "with the channel bindings prefix followed by a colon (ASCII 0x3A)."

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   Thus the channel bindings of the initiator are verified when the
   target verifies the verifier via GSS_VerifyMIC().  Similarly, the
   channel bindings of the target are verified when the initiator
   verifies the verifier of the RPC reply via GSS_VerifyMIC().  Errors
   are handled the same way as described in Section of [2].

3.4.  New Security Service - rpc_gss_svc_channel_prot

         enum rpc_gss_service_t {
             /* Note: the enumerated value for 0 is reserved. */
             rpc_gss_svc_none = 1,
             rpc_gss_svc_integrity = 2,
             rpc_gss_svc_privacy = 3,
             rpc_gss_svc_channel_prot = 4 /* new */

   The rpc_gss_svc_channel_prot service is valid only if RPCSEC_GSSv2 is
   being used, an RPCSEC_GSS_BIND_CHANNEL procedure has been executed
   successfully, and the secure channel still exists.  When
   rpc_gss_svc_channel_prot is used, the RPC requests and replies are
   similar to those of rpc_gss_svc_none except that the verifiers on the
   request and reply always have the flavor set to AUTH_NONE, and the
   contents are zero length.

   Note that even though NULL verifiers are used when
   rpc_gss_svc_channel_prot is used, non-NULL RPCSEC_GSS credentials are
   used.  The same credential is used as before, except that service
   field is set to rpc_gss_svc_channel_prot.

4.  Version Negotiation

   An initiator that supports version 2 of RPCSEC_GSS simply issues an
   RPCSEC_GSS request with the version field set to RPCSEC_GSS_VERS_2.
   If the target does not recognize RPCSEC_GSS_VERS_2, the target will
   return an RPC error per section 5.1 of [2].

   The initiator MUST NOT attempt to use an RPCSEC_GSS handle returned
   by version 2 of a target with version 1 of the same target.  The
   initiator MUST NOT attempt to use an RPCSEC_GSS handle returned by
   version 1 of a target with version 2 of the same target.

5.  Implementation Notes

   Once a successful RPCSEC_GSS_BIND_CHANNEL procedure has been
   performed on an RPCSEC_GSSv2 context handle, the initiator's
   implementation may map application requests for rpc_gss_svc_none and

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   rpc_gss_svc_integrity to rpc_gss_svc_channel_prot credentials.  And
   if the secure channel has privacy enabled, requests for
   rpc_gss_svc_privacy can also be mapped to rpc_gss_svc_channel_prot.

6.  Acknowledgements

   Nico Williams had the idea for extending RPCSEC_GSS to support
   channel bindings.

7.  Security Considerations

   The security considerations are the same as [2].

8.  IANA Considerations


9.  Normative References

   [1]  Bradner, S., "Key words for use in RFCs to Indicate Requirement
        Levels", March 1997.

   [2]  Eisler, M., Chiu, A., and L. Ling, "RPCSEC_GSS Protocol
        Specification", RFC 2203, September 1997.

   [3]  Williams, N., "On the Use of Channel Bindings to Secure
        Channels", RFC 5056, November 2007.

Author's Address

   Mike Eisler
   5765 Chase Point Circle
   Colorado Springs, CO  80919

   Phone: +1-719-599-9026
   Email: email2mre-ietf@yahoo.com

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