IUTF8 Terminal Mode in Secure Shell (SSH)
draft-sgtatham-secsh-iutf8-04

Abstract

This document updates RFC 4254 by specifying 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.

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Table of Contents

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

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.

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.