Network Working Group                                          B. Harris
Internet-Draft                                             February 2007
Intended status: Standards Track
Expires: August 5, 2007


    Extended packet types for the Secure Shell (SSH) Transport Layer
                                Protocol
                 draft-bjh21-ssh-transport-extension-02

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Copyright Notice

   Copyright (C) The IETF Trust (2007).

Abstract

   This memo introduces a new message type into the Secure Shell (SSH)
   Transport Layer Protocol whose meaning and contents are defined by a
   name at the start of the message, thus allowing for further
   extensions to the protocol to be implemented without using further
   message numbers.

   Comments are solicited and should be addressed to the mailing list at



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   <ietf-ssh@NetBSD.org> or to the author.


.  Introduction

   Secure Shell (SSH) [RFC4251] is a secure remote-login protocol.  Its
   transport layer is designed to be extensible, and in particular the
   various cryptographic algorithms that it uses are identified by
   names, which are strings of up to 64 ASCII characters.
   Significantly, names ending with '@' followed by a domain name are
   reserved for allocation by the owner of the corresponding domain.

   Individual messages in SSH, though, have their meaning specified by a
   single byte at the start.  Only 19 of these message numbers are
   available for generic transport-layer purposes, and at the time of
   writing six have already been allocated.  This shortage of message
   numbers, and the requirement that they be allocated by Standards
   Action, increases the difficulty of developing extensions to the SSH
   Transport Layer Protocol that require new messages.

   This document aims to alleviate this problem by allocating one
   message number for extensions to the transport layer protocol, with
   the type of the packet being identified by name.  This is not
   intended to preclude the allocation of new message numbers for
   extensions for which named messages would have an excessive
   performance impact.


.  Conventions Used in this Document

   The key word "MUST" in this document is to be interpreted as
   described in [RFC2119].

   The data types "byte" and "string" are defined in section 5 of
   [RFC4251].

   Other terminology and symbols have the same meaning as in [RFC4253].


.  Extension Message Format

   The format of the message is:

       byte      SSH_MSG_TRANSPORT_EXTENSION
       string    extension name
       ...       extension-specific fields

   The meaning of the message and the contents of 'extension-specific



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   fields' are determined by 'extension name', which follows the
   conventions described in section 4.6.1 of [RFC4250].

   If an implementation receives an SSH_MSG_TRANSPORT_EXTENSION whose
   'extension name' it does not recognise, it MUST treat it as if the
   message number were unrecognised and return SSH_MSG_UNIMPLEMENTED as
   specified in section 11.4 of [RFC4253].


.  Message Number

   The following message number is defined:

       SSH_MSG_TRANSPORT_EXTENSION  XXX


.  Security Considerations

   The security considerations in [RFC4251] apply.


.  IANA Considerations

   IANA should assign a Message Number in the range 1 to 19 for
   SSH_MSG_TRANSPORT_EXTENSION in accordance with section 4.1 of
   [RFC4250].

   IANA should maintain a register of Transport Layer Extension Packet
   Names following the conventions and instructions in section 4.6 of
   [RFC4250].


.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC4250]  Lehtinen, S. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Assigned Numbers", RFC 4250, January 2006.

   [RFC4251]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Protocol Architecture", RFC 4251, January 2006.

   [RFC4253]  Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
              Transport Layer Protocol", RFC 4253, January 2006.






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Trademark Notice

   "SSH" is a registered trademark in the United States.


Author's Address

   Ben Harris
   2a Eachard Road
   CAMBRIDGE  CB3 0HY
   GB

   Email: bjh21@bjh21.me.uk






































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