Secure Shell Public Key Subsystem
RFC 4819

Network Working Group                                       J. Galbraith
Request for Comments: 4819                                   J. Van Dyke
Category: Standards Track                               VanDyke Software
                                                               J. Bright
                                                          Silicon Circus
                                                              March 2007

                   Secure Shell Public Key Subsystem

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.

Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   Secure Shell defines a user 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.

   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 various restrictions,
   including a mandatory command or subsystem.

Galbraith, et al.           Standards Track                     [Page 1]
RFC 4819           Secure Shell Public Key Subsystem          March 2007

Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Public Key Subsystem Overview  . . . . . . . . . . . . . . . .  3
     3.1.  Opening the Public Key Subsystem . . . . . . . . . . . . .  4
     3.2.  Requests and Responses . . . . . . . . . . . . . . . . . .  5
     3.3.  The Status Message . . . . . . . . . . . . . . . . . . . .  5
       3.3.1.  Status Codes . . . . . . . . . . . . . . . . . . . . .  5
     3.4.  The Version Packet . . . . . . . . . . . . . . . . . . . .  6
   4.  Public Key Subsystem Operations  . . . . . . . . . . . . . . .  7
     4.1.  Adding a Public Key  . . . . . . . . . . . . . . . . . . .  7
     4.2.  Removing a Public Key  . . . . . . . . . . . . . . . . . . 10
     4.3.  Listing Public Keys  . . . . . . . . . . . . . . . . . . . 10
     4.4.  Listing Server Capabilities  . . . . . . . . . . . . . . . 10
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
     6.1.  Registrations  . . . . . . . . . . . . . . . . . . . . . . 12
     6.2.  Names  . . . . . . . . . . . . . . . . . . . . . . . . . . 12
       6.2.1.  Conventions for Names  . . . . . . . . . . . . . . . . 12
       6.2.2.  Future Assignments of Names  . . . . . . . . . . . . . 13
     6.3.  Public Key Subsystem Request Names . . . . . . . . . . . . 13
     6.4.  Public Key Subsystem Response Names  . . . . . . . . . . . 13
     6.5.  Public Key Subsystem Attribute Names . . . . . . . . . . . 13
     6.6.  Public Key Subsystem Status Codes  . . . . . . . . . . . . 14
       6.6.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . 14
       6.6.2.  Initial Assignments  . . . . . . . . . . . . . . . . . 14
       6.6.3.  Future Assignments . . . . . . . . . . . . . . . . . . 15
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 15
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16

Galbraith, et al.           Standards Track                     [Page 2]
RFC 4819           Secure Shell Public Key Subsystem          March 2007

1.  Introduction

   Secure Shell (SSH) is a protocol for secure remote login and other
   secure network services over an insecure network.  Secure Shell
   defines a user 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