rfc1961.txt

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Network Working Group                                         P. McMahon
Request for Comments: 1961                                           ICL
Category: Standards Track                                      June 1996


           GSS-API Authentication Method for SOCKS Version 5

Status of this Memo

   This document specifies an Internet standards track protocol for the
   Internet community, and requests discussion and suggestions for
   improvements.  Please refer to the current edition of the "Internet
   Official Protocol Standards" (STD 1) for the standardization state
   and status of this protocol.  Distribution of this memo is unlimited.

Table of Contents

         1. Purpose ............................................ 1
         2. Introduction ....................................... 1
         3. GSS-API Security Context Establishment ............. 2
         4. GSS-API Protection-level Options ................... 5
         5. GSS-API Per-message Protection ..................... 7
         6. GSS-API Security Context Termination ............... 8
         7. References ......................................... 8
         8. Acknowledgments .................................... 8
         9. Security Considerations ............................ 8
         10. Author's Address .................................. 9

1. Purpose

   The protocol specification for SOCKS Version 5 specifies a
   generalized framework for the use of arbitrary authentication
   protocols in the initial SOCKS connection setup.  This document
   provides the specification for the SOCKS V5 GSS-API authentication
   protocol, and defines a GSS-API-based encapsulation for provision of
   integrity, authentication and optional confidentiality.

2. Introduction

   GSS-API provides an abstract interface which provides security
   services for use in distributed applications, but isolates callers
   from specific security mechanisms and implementations.

   GSS-API peers achieve interoperability by establishing a common
   security mechanism for security context establishment - either
   through administrative action, or through negotiation.  GSS-API is
   specified in [RFC 1508], and [RFC 1509].  This specification is
   intended for use with implementations of GSS-API, and the emerging



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RFC 1961          GSS-API Authentication for SOCKS V5          June 1996


   GSS-API V2 specification.

   The approach for use of GSS-API in SOCKS V5 is to authenticate the
   client and server by successfully establishing a GSS-API security
   context - such that the GSS-API encapsulates any negotiation protocol
   for mechanism selection, and the agreement of security service
   options.

   The GSS-API enables the context initiator to know what security
   services the target supports for the chosen mechanism.  The required
   level of protection is then agreed by negotiation.

   The GSS-API per-message protection calls are subsequently used to
   encapsulate any further TCP and UDP traffic between client and
   server.

3. GSS-API Security Context Establishment

3.1 Preparation

   Prior to use of GSS-API primitives, the client and server should be
   locally authenticated, and have established default GSS-API
   credentials.

   The client should call gss_import_name to obtain an internal
   representation of the server name.  For maximal portability the
   default name_type GSS_C_NULL_OID should be used to specify the
   default name space, and the input name_string should treated by the
   client's code as an opaque name-space specific input.

   For example, when using Kerberos V5 naming, the imported name may be
   of the form "SERVICE:socks@socks_server_hostname" where
   "socks_server_hostname" is the fully qualified host name of the
   server with all letters in lower case. Other mechanisms may, however,
   have different name forms, so the client should not make assumptions
   about the name syntax.

3.2 Client Context Establishment

   The client should then call gss_init_sec_context, typically passing:

         GSS_C_NO_CREDENTIAL into cred_handle to specify the default
         credential (for initiator usage),

         GSS_C_NULL_OID into mech_type to specify the default
         mechanism,





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RFC 1961          GSS-API Authentication for SOCKS V5          June 1996


         GSS_C_NO_CONTEXT into context_handle to specify a NULL
         context (initially), and,

         the previously imported server name into target_name.

   The client must also specify its requirements for replay protection,
   delegation, and sequence protection via the gss_init_sec_context
   req_flags parameter.  It is required by this specification that the
   client always requests these service options (i.e. passes
   GSS_C_MUTUAL_FLAG | GSS_C_REPLAY_FLAG | GSS_C_DELEG_FLAG |
   GSS_C_SEQUENCE_FLAG into req_flags).

   However, GSS_C_SEQUENCE_FLAG should only be passed in for TCP-based
   clients, not for UDP-based clients.

3.3 Client Context Establishment Major Status codes

   The gss_init_sec_context returned status code can take two different
   success values:

    - If gss_init_sec_context returns GSS_S_CONTINUE_NEEDED, then the
      client should expect the server to issue a token in the
      subsequent subnegotiation response.  The client must pass the
      token to another call to gss_init_sec_context, and repeat this
      procedure until "continue" operations are complete.

    - If gss_init_sec_context returns GSS_S_COMPLETE, then the client
      should respond to the server with any resulting output_token.

      If there is no output_token, the client should proceed to send
      the protected request details, including any required message
      protection subnegotiation as specified in sections 4 and 5
      below.

3.4 Client initial token

   The client's GSS-API implementation then typically responds with the
   resulting output_token which the client sends in a message to the
   server.

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






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RFC 1961          GSS-API Authentication for SOCKS V5          June 1996


    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 1 to represent an
      authentication message

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

    - "token" is the opaque authentication token emitted by GSS-API

3.5 Client GSS-API Initialisation Failure

   If, however, the client's GSS-API implementation failed during
   gss_init_sec_context, the client must close its connection to the
   server.

3.6 Server Context Establishment

   For the case where a client successfully sends a token emitted by
   gss_init_sec_context() to the server, the server must pass the
   client-supplied token to gss_accept_sec_context as input_token.

   When calling gss_accept_sec_context() for the first time, the
   context_handle argument is initially set to GSS_C_NO_CONTEXT.

   For portability, verifier_cred_handle is set to GSS_C_NO_CREDENTIAL
   to specify default credentials (for acceptor usage).

   If gss_accept_sec_context returns GSS_CONTINUE_NEEDED, the server
   should return the generated output_token to the client, and
   subsequently pass the resulting client supplied token to another call
   to gss_accept_sec_context.

   If gss_accept_sec_context returns GSS_S_COMPLETE, then, if an
   output_token is returned, the server should return it to the client.

   If no token is returned, a zero length token should be sent by the
   server to signal to the client that it is ready to receive the
   client's request.










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RFC 1961          GSS-API Authentication for SOCKS V5          June 1996


3.7 Server Reply

   In all continue/confirmation cases, the server uses the same message
   type as for the client -> server interaction.

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

3.8 Security Context Failure

   If the server refuses the client's connection for any reason (GSS-API
   authentication failure or otherwise), it will return:

    +------+------+
    + ver  | mtyp |
    +------+------+
    + 0x01 | 0xff |
    +------+------+

    Where: