[Docs] [txt|pdf] [Tracker] [Email] [Diff1] [Diff2] [Nits]

Versions: 00 01 02

Secure Shell Working Group                                  J. Galbraith
Internet-Draft                                               J. Van Dyke
Expires: December 22, 2003                                    B. McClure
                                                        VanDyke Software
                                                           June 23, 2003


                   Secure Shell Public-Key Subsystem
              draft-galb-secsh-publickey-subsystem-02.txt

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026.

   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."

   The list of current Internet-Drafts can be accessed at http://
   www.ietf.org/ietf/1id-abstracts.txt.

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This Internet-Draft will expire on December 22, 2003.

Copyright Notice

   Copyright (C) The Internet Society (2003). All Rights Reserved.

Abstract

   SECSH defines an authentication mechanism that is based on public
   keys, but does not define any mechanism for key distribution. No
   common key management solution exists in current implementations.
   This document describes a protocol that can be used to configure
   public keys in an implementation-independent fashion, allowing client
   software to take on the burden of this configuration.

   This protocol is intended to be used from the Secure Shell Connection
   Protocol [4] as a subsystem, as described in Section ``Starting a
   Shell or a Command''. The subsystem name used with this protocol is
   "publickey@vandyke.com".



Galbraith, et al.      Expires December 22, 2003                [Page 1]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


   The public-key subsystem provides a server-independent mechanism for
   clients to add public keys, remove public keys, and list the current
   public keys known by the server. Rights to manage public keys are
   specific and limited to the authenticated user.

   A public key may also be associated with a mandatory command.

Table of Contents

   1.    Introduction . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.    Public-Key Subsystem Overview  . . . . . . . . . . . . . . .  4
   2.1   Opening the Public-Key Subsystem . . . . . . . . . . . . . .  4
   2.2   Requests . . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.3   Responses  . . . . . . . . . . . . . . . . . . . . . . . . .  5
   2.3.1 The Status Response  . . . . . . . . . . . . . . . . . . . .  5
   3.    Public-Key Subsystem Operations  . . . . . . . . . . . . . .  7
   3.1   Version Packet . . . . . . . . . . . . . . . . . . . . . . .  7
   3.2   Adding a public key  . . . . . . . . . . . . . . . . . . . .  7
   3.3   Removing a public key  . . . . . . . . . . . . . . . . . . .  7
   3.4   Listing public keys  . . . . . . . . . . . . . . . . . . . .  8
   3.5   Associate public key with a mandatory command  . . . . . . .  8
         References . . . . . . . . . . . . . . . . . . . . . . . . .  9
         Authors' Addresses . . . . . . . . . . . . . . . . . . . . .  9
         Intellectual Property and Copyright Statements . . . . . . . 11



























Galbraith, et al.      Expires December 22, 2003                [Page 2]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


1. Introduction

   SECSH is a protocol for secure remote login and other secure network
   services over an insecure network. SECSH defines an authentication
   mechanism that is based on public keys, but does not define any
   mechanism for key distribution. Common practice is to authenticate
   once with password authentication and transfer the public key to the
   server.  However, to date no two implementations use the same
   mechanism to configure a public key for use.

   This document describes a subsystem that can be used to configure
   public keys in an implementation-independent fashion. This approach
   allows client software to take on the burden of this configuration.
   The public-key subsystem protocol is designed for extreme simplicity
   in implementation. It is not intended as a PKIX replacement.

   The Secure Shell Public-Key subsystem has been designed to run on top
   of the SECSH transport layer [2] and user authentication     protocols
   [3]. It provides a simple mechanism for the client to manage public
   keys on the server.

   This document should be read only after reading the SECSH
   architecture [1] and SECSH connection [4] documents.

   This protocol requires that the user be able to authenticate in some
   fashion before it can be used. If password authentication is used,
   servers SHOULD provide a configuration option to disable the use of
   password authentication after the first public key is added.























Galbraith, et al.      Expires December 22, 2003                [Page 3]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


2. Public-Key Subsystem Overview

   The public-key subsystem provides a server-independent mechanism for
   clients to add public keys, remove public keys, and list the current
   public keys known by the server.  The subsystem name is
   "publickey@vandyke.com".

   The public keys added, removed, and listed using this protocol are
   specific and limited to those of the authenticated user.

   The operations to add, remove and list the authenticated user's
   public keys are performed as request packets sent to the server. The
   server sends response packets that indicate success or failure as
   well as provide specific response data.

   The format of public-key blobs are detailed in the SSH Transport
   Protocol document [2].

2.1 Opening the Public-Key Subsystem

   The public-key subsystem is opened when the clients sends a
   SSH_MSG_CHANNEL_REQUEST over an existing session.

   The details of how a session is opened are described in the SSH
   Connection Protocol document [4] in the section "Opening a Session".

   To open the public-key subsystem, the client sends:

        byte      SSH_MSG_CHANNEL_REQUEST
        uint32    recipient channel
        string    "subsystem"
        boolean   want reply
        string    "publickey@vandyke.com"

   Client implementations SHOULD reject this request; it is normally
   only sent by the client.

   If want reply is TRUE, the server MUST respond with
   SSH_MSG_CHANNEL_SUCCESS if the public-key subsystem was successfully
   started or SSH_MSG_CHANNEL_FAILURE if the server failed to start or
   does not support the public-key subsystem.

   The server SHOULD respond with SSH_MSG_CHANNEL_FAILURE if the user
   authenticated with a restricted public key that does not allow access
   to the publickey subsystem.

   It is RECOMMENDED that clients request and check the reply for this
   request.



Galbraith, et al.      Expires December 22, 2003                [Page 4]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


2.2 Requests

   All public-key subsystem requests are sent in the following form:

        uint32    length
        string    request-name
        ... request specific data follows

   The length field describes the length of the request-name field and
   the request-specific data, but not of the length field itself.  The
   client MUST receive a response to each request prior to sending a
   new request.

   All requests described in Section 3 are a description of the
   'request-name' and 'data' portions of the packet.

2.3 Responses

   All public-key subsystem responses are sent in the following form:

        uint32    length
        string    response-name
        ... response specific data follows


2.3.1 The Status Response

   A request is acknowledged by sending a status packet. If there is
   data in response to the request, the status packet is sent after all
   data has been sent.

        string    "status"
        uint32    status code
        string    description [RFC-2279]
        string    language tag [RFC-1766]

   A status message MUST be sent for any unrecognized packets and the
   request SHOULD NOT close the subsystem.

2.3.1.1 Status Codes

   The status code gives the status in a more machine-readable format
   (suitable for localization), and can have the following values:

        SSH_PUBLICKEY_SUCCESS                      0
        SSH_PUBLICKEY_ACCESS_DENIED                1
        SSH_PUBLICKEY_STORAGE_EXCEEDED             2
        SSH_PUBLICKEY_REQUEST_NOT_SUPPORTED        3
        SSH_PUBLICKEY_KEY_NOT_FOUND                4
        SSH_PUBLICKEY_KEY_NOT_SUPPORTED            5
      SSH_PUBLICKEY_KEY_ALREADY_PRESENT          6



Galbraith, et al.      Expires December 22, 2003                [Page 5]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


        SSH_PUBLICKEY_GENERAL_FAILURE              7


















































Galbraith, et al.      Expires December 22, 2003                [Page 6]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


3. Public-Key Subsystem Operations

   The public-key subsystem currently defines four operations: add,
   remove, list, and command.

3.1 Version Packet

   Both sides MUST start by sending a version packet that indicates the
   version of the protocol they are using.

        string "version"
        uint32 protocol-version-number

   The version of the protocol described by this document is version 1.

   Both sides send the highest version that they implement. The lower of
   the version numbers is the version of the protocol to use.  If either
   side can't support the lower version, it should close the subsystem
   and notify the other side by sending an SSH_MSG_CHANNEL_CLOSE message.

   Both sides MUST wait to receive this version before continuing.

3.2 Adding a public key

   If the client wishes to add a public key, the client sends:

        string    "add"
        string    public-key algorithm name
        string    public-key blob
      boolean   overwrite
        uint32    attribute-count
                string attrib-name
                string attrib-value
                bool   mandatory
        repeated attribute-count times

   The server MUST attempt to store the public key for the user in the
   appropriate location so the public key can be used for subsequent
   public-key authentications.  If the overwrite field is false and the
   specified key already exists, the server MUST return
   SSH_PUBLICKEY_KEY_ALREADY_PRESENT.  If the server returns this, the
   client SHOULD provide an option to the user to overwrite the key.
   If the overwrite field is true and the specified key already exists
   but cannot be overwritten, the server MUST return
   SSH_PUBLICKEY_ACCESS_DENIED.

   Attribute names are defined following the same scheme laid out for
   algorithm names in [SSH-ARCH] (section 5).  If the server does not
   implement a mandatory attribute, it MUST fail the add.  For the
   purposes of a mandatory attribute, storage of the attribute is not
   sufficient, but requires that the server understand and implement
   the intent of the attribute.

   The following attributes are currently defined:

   "comment"
       The comment field contains user-specified text about the
       public key.  The server SHOULD make every effort to preserve
       this value and return it with the key during a list operation.
       The server MUST NOT attempt to interpret or act upon the content
       of the comment field in any way.

       The comment field is useful so the user can identify the key
       without resorting to comparing its fingerprint.

       This attribute SHOULD NOT be mandatory.

   "comment-language"
       If this attribute is specified, it MUST immediately follow a
       "comment" attribute and specifies the language for that attribute
       [RFC1766].  The client MAY specify more than comment if it
       additionally specifies a different language for each of those
       comments.  The server SHOULD attempt to store each comment,
       together with that comment's lanuage attribute.

       This attribute SHOULD NOT be mandatory.

   "command"
       "command" bypasses the session channel "exec" and "shell" requests
       by always executing the specified command (as if it had been
       executed using an "exec" request).

       This attribute SHOULD be mandatory.  This attribute MUST NOT be
       specified if the "subsystem" attribute is specified.

   "subsystem"
       "subsystem" specifies that the specified subsystem should be started
       when this key is used (as if it had been started using a "subsystem"
       request.

       This attribute SHOULD be mandatory.  This attribute MUST NOT be
       specified if the "command" attribute is specified.

   "restrict"
       The value of this attribute contains server functions that may
       not be performed when this key is used.  It is a comma seperated
       list.  Element names are specified in the same way as attribute
       names, above.  The following restrictions are currently defined:

       Currently defined restrictions are:

        "x11"
        "shell"
        "exec"
        "agent"
        "env"
        "subsystem"

         The "x11" restriction specifies that X11 forwarding may not be
       performed when this key is in use.  The "shell" restriction
       specifies that session channel "shell" requests should be denied
       when this key is in use.  The "exec" restriction specifies that
       session channel "exec" requests should be denied when this key
       is in use.  The "agent" restriction specifies that session channel
       "auth-agent-req" requests should be denied when this key is in use.
       The "env" restriction specifies that session channel "env" requests
       should be denied when this key is in use.  The "subsystem"
       restriction specifies that subsystems may not be started when this
       public key is in use (if the "subsystem" attribute is also specified,
       the subsystem specified in that attribute is exempted from this
       restriction).

       This attribute SHOULD be mandatory.

   "port-forward"
       "port-forward" specifies that no "direct-tcpip" requests should be
       accepted, except to those hosts specified in the comma-separated
       list supplied as a value to this attribute.  If the value of this
       attribute is empty, all "direct-tcpip" requests should be refused
       when using this key.

       This attribute SHOULD be mandatory.

   "reverse-forward"
       "reverse-forward" specifies that no "tcpip-forward" requests should
       be accepted, accept for the port numbers in the comma-separated
       list supplied as a value to this attribute.  If the value of this
       attribute is empty, all "tcpip-forward" requests should be refused
       when using this key.

       This attribute SHOULD be mandatory.

   In addition to the attributes and restrictions specified by the client,
   the server MAY provide a method for administrators to compulsorily enforce
   certain attributes or restrictions.

3.3 Removing a public key

   If the client wishes to remove a public key, the client sends:

        string    "remove"
        string    public-key algorithm name
        string    public-key blob

   The server MUST attempt to remove the public key for the user from
   the appropriate location, so that the public key cannot be used for
   subsequent authentications.



Galbraith, et al.      Expires December 22, 2003                [Page 7]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


3.4 Listing public keys

   If the client wishes to list the known public keys, the client sends:

        string    "list"

   The server will respond with zero or more of the following responses:

        string    "publickey"
        string    public-key algorithm name
        string    public-key blob
        uint32    attribute-count
                string attrib-name
                string attrib-value
        repeated attribute-count times

   Following the last "publickey" response, a status packet MUST be
   sent.

   An implementation MAY choose not to support this request.

3.5 Listing server capabilities

   If the client wishes to know which restrictions the server supports,
   it sends:

      string    "listattributes"

   The server will respond with zero or more of the following responses:

      string    "attribute"
      string    attribute name
      boolean   compulsory

   The server will then respond with zero or more of the following
   responses:

      string    "restriction"
      string    restriction name
      boolean   compulsory

   The server MAY include "restrict" in the list of attributes it supports.
   The client SHOULD NOT require the server to do so in order to accept
   that the server supports the list of restrictions returned by the
   server.

   Following the last "restriction" response, a status packet MUST be
   sent.

   An implementation MAY choose not to support this request.













Galbraith, et al.      Expires December 22, 2003                [Page 8]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


References

   [1]  Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S.
        Lehtinen, "SSH Protocol Architecture",
        draft-ietf-secsh-architecture-13 (work in progress), January
        2002.

   [2]  Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S.
        Lehtinen, "SSH Transport Layer Protocol",
        draft-ietf-secsh-transport-15 (work in progress), March 2002.

   [3]  Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S.
        Lehtinen, "SSH Authentication Protocol",
        draft-ietf-secsh-userauth-16 (work in progress), February 2002.

   [4]  Ylonen, T., Kivinen, T., Saarinen, M., Rinne, T. and S.
        Lehtinen, "SSH Connection Protocol", draft-ietf-secsh-connect-16
        (work in progress), January 2002.

   [5]  Yergeau, F., "UTF-8, a transformation format of ISO 10646", RFC
        2279, January 1998.


Authors' Addresses

   Joseph Galbraith
   VanDyke Software
   4848 Tramway Ridge Blvd
   Suite 101
   Albuquerque, NM  87111
   US

   Phone: +1 505 332 5700
   EMail: galb-list@vandyke.com


   Jeff P. Van Dyke
   VanDyke Software
   4848 Tramway Ridge Blvd
   Suite 101
   Albuquerque, NM  87111
   US

   Phone: +1 505 332 5700
   EMail: jpv@vandyke.com






Galbraith, et al.      Expires December 22, 2003                [Page 9]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


   Brent McClure
   VanDyke Software
   4848 Tramway Ridge Blvd
   Suite 101
   Albuquerque, NM  87111
   US

   Phone: +1 505 332 5700
   EMail: bdm@vandyke.com










































Galbraith, et al.      Expires December 22, 2003               [Page 10]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


Intellectual Property Statement

   The IETF takes no position regarding the validity or scope of any
   intellectual property or other rights that might be claimed to
   pertain to the implementation or use of the technology described in
   this document or the extent to which any license under such rights
   might or might not be available; neither does it represent that it
   has made any effort to identify any such rights. Information on the
   IETF's procedures with respect to rights in standards-track and
   standards-related documentation can be found in BCP-11. Copies of
   claims of rights made available for publication and any assurances of
   licenses to be made available, or the result of an attempt made to
   obtain a general license or permission for the use of such
   proprietary rights by implementors or users of this specification can
   be obtained from the IETF Secretariat.

   The IETF invites any interested party to bring to its attention any
   copyrights, patents or patent applications, or other proprietary
   rights which may cover technology that may be required to practice
   this standard. Please address the information to the IETF Executive
   Director.


Full Copyright Statement

   Copyright (C) The Internet Society (2003). All Rights Reserved.

   This document and translations of it may be copied and furnished to
   others, and derivative works that comment on or otherwise explain it
   or assist in its implementation may be prepared, copied, published
   and distributed, in whole or in part, without restriction of any
   kind, provided that the above copyright notice and this paragraph are
   included on all such copies and derivative works. However, this
   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
   Internet organizations, except as needed for the purpose of
   developing Internet standards in which case the procedures for
   copyrights defined in the Internet Standards process must be
   followed, or as required to translate it into languages other than
   English.

   The limited permissions granted above are perpetual and will not be
   revoked by the Internet Society or its successors or assignees.

   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS ALL WARRANTIES, EXPRESS OR IMPLIED, INCLUDING
   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION



Galbraith, et al.      Expires December 22, 2003               [Page 11]

Internet-Draft     Secure Shell Public-Key Subsystem           June 2003


   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.


Acknowledgment

   Funding for the RFC Editor function is currently provided by the
   Internet Society.











































Galbraith, et al.      Expires December 22, 2003               [Page 12]


Html markup produced by rfcmarkup 1.111, available from https://tools.ietf.org/tools/rfcmarkup/