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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-01.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".



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   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



























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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.























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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 will 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.



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2.2 Requests

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

        string    request-name
        ... request specific data follows

   The client MUST receive acknowledgement of each request prior to
   sending a new request.

   All requests described in Section 3 are a description of the 'data'
   portion of the packet.

2.3 Responses

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

        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:

        SUCCESS                      0
        ACCESS_DENIED                1
        STORAGE_EXCEEDED             2
        REQUEST_NOT_SUPPORTED        3
        KEY_NOT_FOUND                4
        KEY_NOT_SUPPORTED            5



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        GENERAL_FAILURE              6


















































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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.

   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    comment
        string    public-key algorithm name
        string    public-key blob

   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.

   The comment field contains user-specified text about the public key
   and MAY be empty.

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.



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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    comment
        string    public-key algorithm name
        string    public-key blob

   The comment field contains user-specified text about the public key
   and MAY be empty.

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

   An implementation MAY choose not to support this request.

3.5 Associate public key with a mandatory command

   If the client wishes to associate a command with a specific public
   key, the client sends:

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

   The request MUST fail if the public key does not already exist on the
   server.

   An implementation MAY choose not to support this request.
















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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






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

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










































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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
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   HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED WARRANTIES OF
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Acknowledgment

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











































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