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INTERNET-DRAFT                                           M. VanHeyningen
<draft-ietf-aft-socks-ssl-00>                       Aventail Corporation
Expires 20 September 1997                                  20 March 1997

                Secure Sockets Layer for SOCKS Version 5


      This document is an Internet-Draft.  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.''


   This document specifies the use of SSL 3.0 and possible successor
   protocols as an authentication method for SOCKS Version 5.  The
   design is similar to, and largely derived from, the integration of
   GSS-API into SOCKS5 [RFC 1961].  A framework is provided for future
   extensions, and the use of other "subauthentication" methods inside
   SSL is supported.


   During the initial SOCKS V5 negotiation, an authentication method is
   negotiated.  The identifier used in the SOCKS5 authentication
   handshake for this method shall be X'86' (134 decimal.)


   The SSL data stream is wrapped for transport over the SOCKS5 data
   stream as follows:

        | VER | STATE | LEN | DATA
        |  1  |   1   |  2  | 0 - 65535

   The VER shall be X'01 for this revision.  The STATE may have four
   different values:

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        Initial handshake     X'01'
        Option negotiation    X'02'
        Data flow             X'03'
        Closing handshake     X'04'

   LEN specifies the number of bytes in the DATA, and shall be MSB-first.


   After the server selects SSL as its authentication method, an initial
   handshake to establish an SSL-secured connection commences with STATE
   of X'01'.

 SSL specific options

   After this handshake all subsequent data is secured via SSL, then in
   the framing specified above.  With STATE of X'02', the client sends a
   list of SSL-specific options it can support:

        | LEN | OPTIONS
        |  1  |  0-255

   The server responds with an identically formatted list of the subset
   of options to be used for this connection.

   At this time, only two options are defined:

        Subauthentication   X'01'
        UDP-Naked           X'10'


   With SSL integration, the handling of UDP data is a tricky issue.
   Unlike GSSAPI-based solutions, SSL is not designed to handle datagram
   traffic.  UDP-Naked specifies that SSL shall be used only to protect
   the control connection of the UDP association, and UDP traffic will
   receive no enhancements.

   It is expected that other options for UDP processing will be defined;
   in general it is expected that the server will choose one UDP method
   from those offered by the client.


   Subauthentication provides a mechanism for embedding a simpler

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   authentication mechanism inside SSL.  For example, some environments
   may use SSL with server-side certificates to establish a secure
   connection to a server, then use cleartext passwords [RFC 1929] inside
   the encrypted connection.

   If the server's option handshake specifies that subauthentication is
   to be used, the client responds with a message specifying the
   authentication methods it supports in this environment; the format is
   identical to that of [RFC 1928, sec 3].

   After negotiating a subauthentication method, subauthentication
   proceeds exactly as it would normally, but inside the SSL-secured data
   stream.  It is expected that only primitive authentication techniques,
   such as cleartext passwords or CHAP [SOCKS-CHAP], will be used as
   subauthentitcation methods.

 Command processing

   After option processing is complete, the authentication method
   finishes.  STATE is set to X'03', and the SOCKS command commences.

 Orderly closure

   Upon connection termination, the terminating side should change STATE
   to X'04' and send an SSL closure handshake; the other side should also
   change its STATE and respond appropriately.


   As with any negotiation-based mechanism, SOCKS5 is subject to
   downgrade attacks.  Both clients and servers should operate only with
   security parameters consistent with the given security policy.

   The UDP-Naked option, as its name suggests, provides very minimal
   security for UDP traffic.  It allows subauthentication and initial
   commands which may specifiy destination and other use restrictions on
   a UDP association to be established securely, but it does nothing to
   preserve the privacy or integrity of the bulk data.  More secure
   methods of proxying UDP traffic may be added as additional
   SSL-specific options.

   All SSL-based considerations, such as the importance of properly
   seeding random generators used to generate keying information and
   storing persistent keying information in secure ways, apply here.

   SSL 2.0 has known weakness and limitations.  Since there is no
   existing base of software using this specification based on SSL 2.0,
   applications may support SSL 3.0 (or later) only without compromising

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

   [RFC 1929] Leech, M., "Username/Password Authentication for SOCKS V5,"
   March 1996.

   [RFC 1961] McMahon, P., "GSS-API Authentication Method for SOCKS
   Version 5," June 1996.

   [SOCKS-CHAP] VanHeyningen, M., "Challenge-Handshake Authentication
   Protocol for SOCKS V5," <draft-ietf-aft-socks-chap-00>, March 1997,
   work in progress.

   [SSL] Freier, A., Karlton, P., Kocher, P., "The SSL Protocol: Version
   3.0," <draft-ietf-tls-ssl-version3-00.txt>, November 1996, work in


   Marc VanHeyningen
   Aventail Corporation
   117 S. Main Street, Suite 400
   Seattle, WA  98104

   Phone: +1 206 777-5600
   Fax:   +1 206 777-5656
   Email: marcvh@aventail.com

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