IUTF8 Terminal Mode in Secure Shell (SSH)

The Secure Shell (SSH) connection protocol 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 . 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.

The key phrases "SHOULD" and "MAY" in this document are to be interpreted as described in .

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

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

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

The authors are indebted to Colin Watson for originally suggesting this terminal mode in 2006, and David Madore and Jakub Jelen for prior implementation efforts. This document was written using the xml2rfc tool described in .