rfc1961.txt

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    - "ver" is the protocol version number, here 1 to represent the
      first version of the SOCKS/GSS-API protocol

    - "mtyp" is the message type, here 0xff to represent an abort
      message

4. GSS-API Protection-level Options

4.1 Message protection

   Establishment of a GSS-API security context enables comunicating
   peers to determine which per-message protection services are
   available to them through the gss_init_sec_context() and
   gss_accept_sec_context() ret_flags GSS_C_INTEG_FLAG and
   GSS_C_CONF_FLAG which respectively indicate message integrity and
   confidentiality services.

   It is necessary to ensure that the message protection applied to the
   traffic is appropriate to the sensitivity of the data, and the
   severity of the threats.







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RFC 1961          GSS-API Authentication for SOCKS V5          June 1996


4.2 Message Protection Subnegotiation

   For TCP and UDP clients and servers, different levels of protection
   are possible in the SOCKS V5 protocol, so an additional
   subnegotiation stage is needed to agree the message protection level.
   After successful completion of this subnegotiation, TCP and UDP
   clients and servers use GSS-API encapsulation as defined in section
   5.1.

   After successful establishment of a GSS-API security context, the
   client's GSS-API implementation sends its required security context
   protection level to the server.  The server then returns the security
   context protection level which it agrees to - which may or may not
   take the the client's request into account.

   The security context protection level sent by client and server must
   be one of the following values:

         1 required per-message integrity
         2 required per-message integrity and confidentiality
         3 selective per-message integrity or confidentiality based on
           local client and server configurations

   It is anticipated that most implementations will agree on level 1 or
   2 due to the practical difficulties in applying selective controls to
   messages passed through a socks library.

4.3 Message Protection Subnegotiation Message Format

   The security context protection level is sent from client to server
   and vice versa using the following protected message format:

    +------+------+------+.......................+
    + ver  | mtyp | len  |   token               |
    +------+------+------+.......................+
    + 0x01 | 0x02 | 0x02 | up to 2^16 - 1 octets |
    +------+------+------+.......................+

    Where:

    - "ver" is the protocol version number, here 1 to represent the
      first version of the SOCKS/GSS-API protocol

    - "mtyp" is the message type, here 2 to represent a protection
      -level negotiation message

    - "len" is the length of the "token" field in octets




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RFC 1961          GSS-API Authentication for SOCKS V5          June 1996


    - "token" is the GSS-API encapsulated protection level

4.4 Message Protection Subnegotiation Message Generation

   The token is produced by encapsulating an octet containing the
   required protection level using gss_seal()/gss_wrap() with conf_req
   set to FALSE.  The token is verified using gss_unseal()/
   gss_unwrap().

   If the server's choice of protection level is unacceptable to the
   client, then the client must close its connection to the server

5. GSS-API Per-message Protection

   For TCP and UDP clients and servers, the GSS-API functions for
   encapsulation and de-encapsulation shall be used by implementations -
   i.e. gss_seal()/gss_wrap(), and gss_unseal()/ gss_unwrap().

   The default value of quality of protection shall be specified, and
   the use of conf_req_flag shall be as determined by the previous
   subnegotiation step.  If protection level 1 is agreed then
   conf_req_flag MUST always be FALSE; if protection level 2 is agreed
   then conf_req_flag MUST always be TRUE; and if protection level 3 is
   agreed then conf_req is determined on a per-message basis by client
   and server using local configuration.

   All encapsulated messages are prefixed by the following framing:

    +------+------+------+.......................+
    + ver  | mtyp | len  |       token           |
    +------+------+------+.......................+
    + 0x01 | 0x03 | 0x02 | up to 2^16 - 1 octets |
    +------+------+------+.......................+

    Where:

    - "ver" is the protocol version number, here 1 to represent the
      first version of the SOCKS/GSS-API protocol

    - "mtyp" is the message type, here 3 to represent encapulated user
      data

    - "len" is the length of the "token" field in octets

    - "token" is the user data encapsulated by GSS-API






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RFC 1961          GSS-API Authentication for SOCKS V5          June 1996


6. GSS-API Security Context Termination

   The GSS-API context termination message (emitted by
   gss_delete_sec_context) is not used by this protocol.

   When the connection is closed, each peer invokes
   gss_delete_sec_context() passing GSS_C_NO_BUFFER into the
   output_token argument.

7. References

    [RFC 1508] Linn, J., "Generic Security Service API",
               September 1993.

    [RFC 1509] Wray, J., "Generic Security Service API : C-bindings",
               September 1993.

    [SOCKS V5] Leech, M., Ganis, M., Lee, Y., Kuris, R., Koblas, D.,
               and L. Jones, "SOCKS Protocol V5", RFC 1928, April
               1996.

8. Acknowledgment

   This document builds from a previous memo produced by Marcus Leech
   (BNR) - whose comments are gratefully acknowleged.  It also reflects
   input from the AFT WG, and comments arising from implementation
   experience by Xavier Gosselin (IUT Lyons).

9. Security Considerations

   The security services provided through the GSS-API are entirely
   dependent on the effectiveness of the underlying security mechanisms,
   and the correctness of the implementation of the underlying
   algorithms and protocols.

   The user of a GSS-API service must ensure that the quality of
   protection provided by the mechanism implementation is consistent
   with their security policy.

   In addition, where negotiation is supported under the GSS-API,
   constraints on acceptable mechanisms may be imposed to ensure
   suitability for application to authenticated firewall traversal.









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RFC 1961          GSS-API Authentication for SOCKS V5          June 1996


10. Author's Address

   P. V. McMahon
   ICL Enterprises
   Kings House
   33 Kings Road
   Reading, RG1 3PX
   UK

   EMail: [e-mail]
   Phone: [phone]
   Fax:   [phone]







































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