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Network Working Group                                          S. Tatham
Internet-Draft                                                     PuTTY
Intended status: Standards Track                               D. Tucker
Expires: September 3, 2017                                       OpenSSH
                                                           March 2, 2017


               IUTF8 Terminal Mode in Secure Shell (SSH)
                     draft-sgtatham-secsh-iutf8-06

Abstract

   This document specifies a new opcode in the Secure Shell terminal
   modes encoding.  The new opcode describes the widely used IUTF8
   terminal mode bit, which indicates that terminal I/O uses the UTF-8
   character encoding.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

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   This Internet-Draft will expire on September 3, 2017.

Copyright Notice

   Copyright (c) 2017 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   described in the Simplified BSD License.



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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions Used in This Document . . . . . . . . . . . . . .   2
   3.  New IUTF8 opcode for terminal mode encoding . . . . . . . . .   2
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   3
   5.  Security Considerations . . . . . . . . . . . . . . . . . . .   3
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .   3
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   3
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   3
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   4
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   4

1.  Introduction

   The Secure Shell (SSH) connection protocol [RFC4254] provides an
   encoding for terminal modes, used in the "pty-req" channel request
   type.

   A commonly used terminal mode is IUTF8, which indicates that the
   terminal driver should assume that terminal I/O uses the UTF-8
   character encoding [RFC3629].  This is typically used by the kernel's
   terminal driver on the server to decide how many bytes of input to
   treat as a single logical character during line editing.

   SSH currently does not provide an encoding for IUTF8.  This document
   specifies one.

2.  Conventions Used in This Document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [RFC2119].

3.  New IUTF8 opcode for terminal mode encoding

   The opcode value 42 is defined for the IUTF8 terminal mode.

   As [RFC4254] section 8 specifies for all opcodes in the range 1 to
   159, it is therefore followed by a single uint32 argument.  The value
   0 indicates that the IUTF8 mode is disabled, and the value 1
   indicates that it is enabled.

   As with all other encoded terminal modes, the client SHOULD transmit
   a value for this mode if it knows about one, and the server MAY
   ignore it.





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4.  IANA Considerations

   This document augments the "Encoding of Terminal Modes" list in
   section 8 of [RFC4254].

   IANA is requested to update the SSH encoded terminal modes registry
   with the following additional entry:

   opcode  mnemonic       description
   ------  --------       -----------
   42      IUTF8          Terminal input and output is assumed to be
                           encoded in UTF-8.

                                 Figure 1

5.  Security Considerations

   The security considerations of [RFC4254] apply.  This additional
   terminal mode encoding is believed to have no security implications
   differing from the existing set of encoded terminal modes.

   Since the IUTF8 terminal mode is intended for use in conjunction with
   the UTF-8 character encoding, the security considerations of
   [RFC3629] also apply to systems in which this mode is enabled.  In
   particular, terminal drivers which interpret this bit as enabling
   UTF-8 aware line editing behavior should carefully consider how that
   behavior will treat illegal sequences, overlong encodings and
   redundant representations of composed characters (see [UNICODE]).

6.  Acknowledgements

   The authors are indebted to Colin Watson for originally suggesting
   this terminal mode in 2005, and David Madore and Jakub Jelen for
   prior implementation efforts.

   This document was written using the xml2rfc tool described in
   [RFC7749].

7.  References

7.1.  Normative References

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <http://www.rfc-editor.org/info/rfc2119>.





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   [RFC3629]  Yergeau, F., "UTF-8, a transformation format of ISO
              10646", STD 63, RFC 3629, DOI 10.17487/RFC3629, November
              2003, <http://www.rfc-editor.org/info/rfc3629>.

   [RFC4254]  Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH)
              Connection Protocol", RFC 4254, DOI 10.17487/RFC4254,
              January 2006, <http://www.rfc-editor.org/info/rfc4254>.

7.2.  Informative References

   [RFC7749]  Reschke, J., "The "xml2rfc" Version 2 Vocabulary",
              RFC 7749, DOI 10.17487/RFC7749, February 2016,
              <http://www.rfc-editor.org/info/rfc7749>.

   [UNICODE]  The Unicode Consortium, "The Unicode Standard",
              <http://www.unicode.org/versions/latest/>.

Authors' Addresses

   Simon Tatham
   PuTTY

   Email: anakin@pobox.com


   Darren Tucker
   OpenSSH

   Email: dtucker@openssh.com






















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