RFC 4250 PROPOSED STANDARD SSH · IANA · REGISTRIES
SSH numbers: The Secure Shell (SSH) Protocol Assigned Numbers
The starting contents and rules of the IANA registries for SSH message numbers, reason codes, terminal modes and algorithm names.
RFC EDITOR
Lehtinen, S. and C. Lonvick, Ed., "The Secure Shell (SSH) Protocol Assigned Numbers", RFC 4250, DOI 10.17487/RFC4250, January 2006, <https://www.rfc-editor.org/info/rfc4250>.
BIBTEX
@misc{rfc4250,
series = {Request for Comments},
number = 4250,
howpublished = {RFC 4250},
publisher = {RFC Editor},
doi = {10.17487/RFC4250},
url = {https://www.rfc-editor.org/info/rfc4250},
author = {S. Lehtinen and C. Lonvick},
title = {{The Secure Shell (SSH) Protocol Assigned Numbers}},
pagetotal = 20,
year = 2006,
month = jan,
} RFC text
Contents
Network Working Group S. Lehtinen
Request for Comments: 4250 SSH Communications Security Corp
Category: Standards Track C. Lonvick, Ed.
Cisco Systems, Inc.
January 2006
The Secure Shell (SSH) Protocol Assigned Numbers
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 Internet Society (2006).
Abstract
This document defines the instructions to the IANA and the initial
state of the IANA assigned numbers for the Secure Shell (SSH)
protocol. It is intended only for the initialization of the IANA
registries referenced in the set of SSH documents.
Table of Contents
1. Introduction ....................................................2
2. Contributors ....................................................3
3. Conventions Used in This Document ...............................3
3.1. RFC 2119 Keywords ..........................................3
3.2. RFC 2434 Keywords ..........................................3
3.3. Protocol Fields and Values .................................4
4. IANA Considerations .............................................5
4.1. Message Numbers ............................................5
4.1.1. Conventions .........................................5
4.1.2. Initial Assignments .................................6
4.1.3. Future Assignments ..................................6
4.2. Disconnection Messages Reason Codes and Descriptions .......7
4.2.1. Conventions .........................................7
4.2.2. Initial Assignments .................................7
4.2.3. Future Assignments ..................................8
4.3. Channel Connection Failure Reason Codes and Descriptions ...8
4.3.1. Conventions .........................................8
4.3.2. Initial Assignments .................................8
4.3.3. Future Assignments ..................................8
4.3.4. Notes about the PRIVATE USE Range ...................9
4.4. Extended Channel Data Transfer data_type_code and Data .....9
4.4.1. Conventions .........................................9
4.4.2. Initial Assignments ................................10
4.4.3. Future Assignments .................................10
4.5. Pseudo-Terminal Encoded Terminal Modes ....................10
4.5.1. Conventions ........................................10
4.5.2. Initial Assignments ................................10
4.5.3. Future Assignments .................................12
4.6. Names .....................................................12
4.6.1. Conventions for Names ..............................13
4.6.2. Future Assignments of Names ........................13
4.7. Service Names .............................................13
4.8. Authentication Method Names ...............................14
4.9. Connection Protocol Assigned Names ........................14
4.9.1. Connection Protocol Channel Types ..................14
4.9.2. Connection Protocol Global Request Names ...........14
4.9.3. Connection Protocol Channel Request Names ..........15
4.9.4. Initial Assignment of Signal Names .................15
4.9.5. Connection Protocol Subsystem Names ................15
4.10. Key Exchange Method Names ................................16
4.11. Assigned Algorithm Names .................................16
4.11.1. Encryption Algorithm Names ........................16
4.11.2. MAC Algorithm Names ...............................17
4.11.3. Public Key Algorithm Names ........................17
4.11.4. Compression Algorithm Names .......................17
5. Security Considerations ........................................17
6. References .....................................................18
6.1. Normative References ......................................18
6.2. Informative References ....................................18
Authors' Addresses ................................................19
Trademark Notice ..................................................19
1. Introduction
This document does not define any new protocols. It is intended only
to create the initial state of the IANA databases for the SSH
protocol and also contains instructions for future assignments.
Except for one HISTORIC algorithm generally regarded as obsolete,
this document does not define any new protocols or number ranges not
already defined in: [SSH-ARCH], [SSH-TRANS], [SSH-USERAUTH],
[SSH-CONNECT].
2. Contributors
The major original contributors of this set of documents have been:
Tatu Ylonen, Tero Kivinen, Timo J. Rinne, Sami Lehtinen (all of SSH
Communications Security Corp), and Markku-Juhani O. Saarinen
(University of Jyvaskyla). Darren Moffat was the original editor of
this set of documents and also made very substantial contributions.
Many people contributed to the development of this document over the
years. People who should be acknowledged include Mats Andersson, Ben
Harris, Bill Sommerfeld, Brent McClure, Niels Moller, Damien Miller,
Derek Fawcus, Frank Cusack, Heikki Nousiainen, Jakob Schlyter, Jeff
Van Dyke, Jeffrey Altman, Jeffrey Hutzelman, Jon Bright, Joseph
Galbraith, Ken Hornstein, Markus Friedl, Martin Forssen, Nicolas
Williams, Niels Provos, Perry Metzger, Peter Gutmann, Simon
Josefsson, Simon Tatham, Wei Dai, Denis Bider, der Mouse, and
Tadayoshi Kohno. Listing their names here does not mean that they
endorse this document, but that they have contributed to it.
3. Conventions Used in This Document
3.1. RFC 2119 Keywords
All documents related to the SSH protocols shall use the keywords
"MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD",
"SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" to describe
requirements. These keywords are to be interpreted as described in
[RFC2119].
3.2. RFC 2434 Keywords
The keywords "PRIVATE USE", "HIERARCHICAL ALLOCATION", "FIRST COME
FIRST SERVED", "EXPERT REVIEW", "SPECIFICATION REQUIRED", "IESG
APPROVAL", "IETF CONSENSUS", and "STANDARDS ACTION" that appear in
this document when used to describe namespace allocation are to be
interpreted as described in [RFC2434]. These designations are
repeated in this document for clarity.
PRIVATE USE - For private or local use only, with the type and
purpose defined by the local site. No attempt is made to prevent
multiple sites from using the same value in different (and
incompatible) ways. There is no need for IANA to review such
assignments and assignments are not generally useful for
interoperability.
HIERARCHICAL ALLOCATION - Delegated managers can assign values
provided they have been given control over that part of the name
space. IANA controls the higher levels of the namespace according to
one of the other policies.
FIRST COME FIRST SERVED - Anyone can obtain an assigned number, so
long as they provide a point of contact and a brief description of
what the value would be used for. For numbers, the exact value is
generally assigned by the IANA; with names, specific names are
usually requested.
EXPERT REVIEW - approval by a Designated Expert is required.
SPECIFICATION REQUIRED - Values and their meaning must be documented
in an RFC or other permanent and readily available reference, in
sufficient detail so that interoperability between independent
implementations is possible.
IESG APPROVAL - New assignments must be approved by the IESG, but
there is no requirement that the request be documented in an RFC
(though the IESG has discretion to request documents or other
supporting materials on a case-by-case basis).
IETF CONSENSUS - New values are assigned through the IETF consensus
process. Specifically, new assignments are made via RFCs approved by
the IESG. Typically, the IESG will seek input on prospective
assignments from appropriate persons (e.g., a relevant Working Group
if one exists).
STANDARDS ACTION - Values are assigned only for Standards Track RFCs
approved by the IESG.
3.3. Protocol Fields and Values
Protocol fields and possible values to fill them are defined in this
set of documents. Protocol fields will be defined in the message
definitions. As an example, SSH_MSG_CHANNEL_DATA is defined as
follows.
byte SSH_MSG_CHANNEL_DATA
uint32 recipient channel
string data
Throughout these documents, when the fields are referenced, they will
appear within single quotes. When values to fill those fields are
referenced, they will appear within double quotes. Using the above
example, possible values for 'data' are "foo" and "bar".
4. IANA Considerations
This entire document is the IANA considerations for the SSH protocol,
as defined in [SSH-ARCH], [SSH-TRANS], [SSH-USERAUTH], [SSH-CONNECT].
This section contains conventions used in naming the namespaces, the
initial state of the registry, and instructions for future
assignments.
4.1. Message Numbers
The Message Number is a byte value that describes the payload of a
packet.
4.1.1. Conventions
Protocol packets have message numbers in the range 1 to 255. These
numbers are allocated as follows:
Transport layer protocol:
1 to 19 Transport layer generic (e.g., disconnect, ignore,
debug, etc.)
20 to 29 Algorithm negotiation
30 to 49 Key exchange method specific (numbers can be reused
for different authentication methods)
User authentication protocol:
50 to 59 User authentication generic
60 to 79 User authentication method specific (numbers can be
reused for different authentication methods)
Connection protocol:
80 to 89 Connection protocol generic
90 to 127 Channel related messages
Reserved for client protocols:
128 to 191 Reserved
Local extensions:
192 to 255 Local extensions
4.1.2. Initial Assignments
The following table identifies the initial assignments of the Message
ID values.
Message ID Value Reference
----------- ----- ---------
SSH_MSG_DISCONNECT 1 [SSH-TRANS]
SSH_MSG_IGNORE 2 [SSH-TRANS]
SSH_MSG_UNIMPLEMENTED 3 [SSH-TRANS]
SSH_MSG_DEBUG 4 [SSH-TRANS]
SSH_MSG_SERVICE_REQUEST 5 [SSH-TRANS]
SSH_MSG_SERVICE_ACCEPT 6 [SSH-TRANS]
SSH_MSG_KEXINIT 20 [SSH-TRANS]
SSH_MSG_NEWKEYS 21 [SSH-TRANS]
SSH_MSG_USERAUTH_REQUEST 50 [SSH-USERAUTH]
SSH_MSG_USERAUTH_FAILURE 51 [SSH-USERAUTH]
SSH_MSG_USERAUTH_SUCCESS 52 [SSH-USERAUTH]
SSH_MSG_USERAUTH_BANNER 53 [SSH-USERAUTH]
SSH_MSG_GLOBAL_REQUEST 80 [SSH-CONNECT]
SSH_MSG_REQUEST_SUCCESS 81 [SSH-CONNECT]
SSH_MSG_REQUEST_FAILURE 82 [SSH-CONNECT]
SSH_MSG_CHANNEL_OPEN 90 [SSH-CONNECT]
SSH_MSG_CHANNEL_OPEN_CONFIRMATION 91 [SSH-CONNECT]
SSH_MSG_CHANNEL_OPEN_FAILURE 92 [SSH-CONNECT]
SSH_MSG_CHANNEL_WINDOW_ADJUST 93 [SSH-CONNECT]
SSH_MSG_CHANNEL_DATA 94 [SSH-CONNECT]
SSH_MSG_CHANNEL_EXTENDED_DATA 95 [SSH-CONNECT]
SSH_MSG_CHANNEL_EOF 96 [SSH-CONNECT]
SSH_MSG_CHANNEL_CLOSE 97 [SSH-CONNECT]
SSH_MSG_CHANNEL_REQUEST 98 [SSH-CONNECT]
SSH_MSG_CHANNEL_SUCCESS 99 [SSH-CONNECT]
SSH_MSG_CHANNEL_FAILURE 100 [SSH-CONNECT]
4.1.3. Future Assignments
Requests for assignments of new message numbers in the range of 1 to
29, 50 to 59, and 80 to 127 MUST be done through the STANDARDS ACTION
method, as described in [RFC2434].
The meanings of message numbers in the range of 30 to 49 are specific
to the key exchange method in use, and their meaning will be
specified by the definition of that method.
The meanings of message numbers in the range of 60 to 79 are specific
to the user authentication method in use, and their meaning will be
specified by the definition of that method.
Requests for assignments of new message numbers in the range of 128
to 191 MUST be done through the IETF CONSENSUS method, as described
in [RFC2434].
The IANA will not control the message numbers in the range of 192
through 255. This range will be left for PRIVATE USE.
4.2. Disconnection Messages Reason Codes and Descriptions
The Disconnection Message 'reason code' is a uint32 value. The
associated Disconnection Message 'description' is a human-readable
message that describes the disconnect reason.
4.2.1. Conventions
Protocol packets containing the SSH_MSG_DISCONNECT message MUST have
Disconnection Message 'reason code' values in the range of 0x00000001
to 0xFFFFFFFF. These are described in [SSH-TRANS].
4.2.2. Initial Assignments
The following table identifies the initial assignments of the
SSH_MSG_DISCONNECT 'description' and 'reason code' values.
Symbolic Name reason code
------------- -----------
SSH_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT 1
SSH_DISCONNECT_PROTOCOL_ERROR 2
SSH_DISCONNECT_KEY_EXCHANGE_FAILED 3
SSH_DISCONNECT_RESERVED 4
SSH_DISCONNECT_MAC_ERROR 5
SSH_DISCONNECT_COMPRESSION_ERROR 6
SSH_DISCONNECT_SERVICE_NOT_AVAILABLE 7
SSH_DISCONNECT_PROTOCOL_VERSION_NOT_SUPPORTED 8
SSH_DISCONNECT_HOST_KEY_NOT_VERIFIABLE 9
SSH_DISCONNECT_CONNECTION_LOST 10
SSH_DISCONNECT_BY_APPLICATION 11
SSH_DISCONNECT_TOO_MANY_CONNECTIONS 12
SSH_DISCONNECT_AUTH_CANCELLED_BY_USER 13
SSH_DISCONNECT_NO_MORE_AUTH_METHODS_AVAILABLE 14
SSH_DISCONNECT_ILLEGAL_USER_NAME 15
4.2.3. Future Assignments
Disconnection Message 'reason code' values MUST be assigned
sequentially. Requests for assignments of new Disconnection Message
'reason code' values, and their associated Disconnection Message
'description' text, in the range of 0x00000010 through 0xFDFFFFFF,
MUST be done through the IETF CONSENSUS method, as described in
[RFC2434]. The IANA will not assign Disconnection Message 'reason
code' values in the range of 0xFE000000 through 0xFFFFFFFF.
Disconnection Message 'reason code' values in that range are left for
PRIVATE USE, as described in [RFC2434].
4.3. Channel Connection Failure Reason Codes and Descriptions
The Channel Connection Failure 'reason code' is a uint32 value. The
associated Channel Connection Failure 'description' text is a human-
readable message that describes the channel connection failure
reason. This is described in [SSH-CONNECT].
4.3.1. Conventions
Protocol packets containing the SSH_MSG_CHANNEL_OPEN_FAILURE message
MUST have Channel Connection Failure 'reason code' values in the
range of 0x00000001 to 0xFFFFFFFF.
4.3.2. Initial Assignments
The initial assignments for the 'reason code' values and
'description' values are given in the table below. Note that the
values for the 'reason code' are given in decimal format for
readability, but they are actually uint32 values.
Symbolic Name reason code
------------- -----------
SSH_OPEN_ADMINISTRATIVELY_PROHIBITED 1
SSH_OPEN_CONNECT_FAILED 2
SSH_OPEN_UNKNOWN_CHANNEL_TYPE 3
SSH_OPEN_RESOURCE_SHORTAGE 4
4.3.3. Future Assignments
Channel Connection Failure 'reason code' values MUST be assigned
sequentially. Requests for assignments of new Channel Connection
Failure 'reason code' values, and their associated Channel Connection
Failure 'description string', in the range of 0x00000005 to
0xFDFFFFFF MUST be done through the IETF CONSENSUS method, as
described in [RFC2434]. The IANA will not assign Channel Connection
Failure 'reason code' values in the range of 0xFE000000 to
0xFFFFFFFF. Channel Connection Failure 'reason code' values in that
range are left for PRIVATE USE, as described in [RFC2434].
4.3.4. Notes about the PRIVATE USE Range
While it is understood that the IANA will have no control over the
range of 0xFE000000 to 0xFFFFFFFF, this range will be split in two
parts and administered by the following conventions.
o The range of 0xFE000000 to 0xFEFFFFFF is to be used in conjunction
with locally assigned channels. For example, if a channel is
proposed with a 'channel type' of "example_session@example.com"
but fails, then the server will respond with either a 'reason
code' assigned by the IANA (as listed above and in the range of
0x00000001 to 0xFDFFFFFF), or with a locally assigned value in the
range of 0xFE000000 to 0xFEFFFFFF. Naturally, if the server does
not understand the proposed 'channel type', even if it is a
locally defined 'channel type', then the 'reason code' MUST be
0x00000003, as described above. If the server does understand the
'channel type', but the channel still fails to open, then the
server SHOULD respond with a locally assigned 'reason code' value
that is consistent with the proposed local 'channel type'. It is
assumed that practitioners will first attempt to use the IANA-
assigned 'reason code' values and then document their locally
assigned 'reason code' values.
o There are no restrictions or suggestions for the range starting
with 0xFF. No interoperability is expected for anything used in
this range. Essentially, it is for experimentation.
4.4. Extended Channel Data Transfer data_type_code and Data
The Extended Channel Data Transfer 'data_type_code' is a uint32
value. The associated Extended Channel Data Transfer 'data' is a
human-readable message that describes the type of data allowed to be
transferred in the channel.
4.4.1. Conventions
Protocol packets containing the SSH_MSG_CHANNEL_EXTENDED_DATA message
MUST have Extended Channel Data Transfer 'data_type_code' values in
the range of 0x00000001 to 0xFFFFFFFF. This is described in
[SSH-CONNECT].
4.4.2. Initial Assignments
The initial assignments for the 'data_type_code' values and 'data'
values are given in the table below. Note that the value for the
'data_type_code' is given in decimal format for readability, but the
values are actually uint32 values.
Symbolic name data_type_code
------------- --------------
SSH_EXTENDED_DATA_STDERR 1
4.4.3. Future Assignments
Extended Channel Data Transfer 'data_type_code' values MUST be
assigned sequentially. Requests for assignments of new Extended
Channel Data Transfer 'data_type_code' values, and their associated
Extended Channel Data Transfer 'data' strings, in the range of
0x00000002 to 0xFDFFFFFF, MUST be done through the IETF CONSENSUS
method, as described in [RFC2434]. The IANA will not assign Extended
Channel Data Transfer 'data_type_code' values in the range of
0xFE000000 to 0xFFFFFFFF. Extended Channel Data Transfer
'data_type_code' values in that range are left for PRIVATE USE, as
described in [RFC2434].
4.5. Pseudo-Terminal Encoded Terminal Modes
SSH_MSG_CHANNEL_REQUEST messages with a "pty-req" string MUST contain
'encoded terminal modes'. The 'encoded terminal modes' value is a
byte stream of opcode-argument pairs.
4.5.1. Conventions
Protocol packets containing the SSH_MSG_CHANNEL_REQUEST message with
a "pty-req" string MUST contain an 'encoded terminal modes' value.
The opcode values consist of a single byte and are in the range of 1
to 255. Opcodes 1 to 159 have a uint32 argument. Opcodes 160 to 255
are not yet defined.
4.5.2. Initial Assignments
The following table identifies the initial assignments of the opcode
values that are used in the 'encoded terminal modes' value.
opcode mnemonic description
------ -------- -----------
0 TTY_OP_END Indicates end of options.
1 VINTR Interrupt character; 255 if none. Similarly
for the other characters. Not all of these
characters are supported on all systems.
2 VQUIT The quit character (sends SIGQUIT signal on
POSIX systems).
3 VERASE Erase the character to left of the cursor.
4 VKILL Kill the current input line.
5 VEOF End-of-file character (sends EOF from the
terminal).
6 VEOL End-of-line character in addition to
carriage return and/or linefeed.
7 VEOL2 Additional end-of-line character.
8 VSTART Continues paused output (normally
control-Q).
9 VSTOP Pauses output (normally control-S).
10 VSUSP Suspends the current program.
11 VDSUSP Another suspend character.
12 VREPRINT Reprints the current input line.
13 VWERASE Erases a word left of cursor.
14 VLNEXT Enter the next character typed literally,
even if it is a special character
15 VFLUSH Character to flush output.
16 VSWTCH Switch to a different shell layer.
17 VSTATUS Prints system status line (load, command,
pid, etc).
18 VDISCARD Toggles the flushing of terminal output.
30 IGNPAR The ignore parity flag. The parameter
SHOULD be 0 if this flag is FALSE,
and 1 if it is TRUE.
31 PARMRK Mark parity and framing errors.
32 INPCK Enable checking of parity errors.
33 ISTRIP Strip 8th bit off characters.
34 INLCR Map NL into CR on input.
35 IGNCR Ignore CR on input.
36 ICRNL Map CR to NL on input.
37 IUCLC Translate uppercase characters to
lowercase.
38 IXON Enable output flow control.
39 IXANY Any char will restart after stop.
40 IXOFF Enable input flow control.
41 IMAXBEL Ring bell on input queue full.
50 ISIG Enable signals INTR, QUIT, [D]SUSP.
51 ICANON Canonicalize input lines.
52 XCASE Enable input and output of uppercase
characters by preceding their lowercase
equivalents with "\".
53 ECHO Enable echoing.
54 ECHOE Visually erase chars.
55 ECHOK Kill character discards current line.
56 ECHONL Echo NL even if ECHO is off.
57 NOFLSH Don't flush after interrupt.
58 TOSTOP Stop background jobs from output.
59 IEXTEN Enable extensions.
60 ECHOCTL Echo control characters as ^(Char).
61 ECHOKE Visual erase for line kill.
62 PENDIN Retype pending input.
70 OPOST Enable output processing.
71 OLCUC Convert lowercase to uppercase.
72 ONLCR Map NL to CR-NL.
73 OCRNL Translate carriage return to newline
(output).
74 ONOCR Translate newline to carriage
return-newline (output).
75 ONLRET Newline performs a carriage return
(output).
90 CS7 7 bit mode.
91 CS8 8 bit mode.
92 PARENB Parity enable.
93 PARODD Odd parity, else even.
128 TTY_OP_ISPEED Specifies the input baud rate in
bits per second.
129 TTY_OP_OSPEED Specifies the output baud rate in
bits per second.
4.5.3. Future Assignments
Requests for assignments of new opcodes and their associated
arguments MUST be done through the IETF CONSENSUS method, as
described in [RFC2434].
4.6. Names
In the following sections, the values for the name spaces are
textual. The conventions and instructions to the IANA for future
assignments are given in this section. The initial assignments are
given in their respective sections.
4.6.1. Conventions for Names
All names registered by the IANA in the following sections MUST be
printable US-ASCII strings, and MUST NOT contain the characters at-
sign ("@"), comma (","), whitespace, control characters (ASCII codes
32 or less), or the ASCII code 127 (DEL). Names are case-sensitive,
and MUST NOT be longer than 64 characters.
A provision is made here for locally extensible names. The IANA will
not register, and will not control, names with the at-sign in them.
Names with the at-sign in them will have the format of
"name@domainname" (without the double quotes) where the part
preceding the at-sign is the name. The format of the part preceding
the at-sign is not specified; however, these names MUST be printable
US-ASCII strings, and MUST NOT contain the comma character (","),
whitespace, control characters (ASCII codes 32 or less), or the ASCII
code 127 (DEL). They MUST have only a single at-sign in them. The
part following the at-sign MUST be a valid, fully qualified internet
domain name [RFC1034] controlled by the person or organization
defining the name. Names are case-sensitive, and MUST NOT be longer
than 64 characters. It is up to each domain how it manages its local
namespace. It has been noted that these names resemble STD 11
[RFC0822] email addresses. This is purely coincidental and has
nothing to do with STD 11 [RFC0822]. An example of a locally defined
name is "ourcipher-cbc@example.com" (without the double quotes).
4.6.2. Future Assignments of Names
Requests for assignments of new names MUST be done through the IETF
CONSENSUS method, as described in [RFC2434].
4.7. Service Names
The 'service name' is used to describe a protocol layer. The
following table lists the initial assignments of the 'service name'
values.
Service Name Reference
------------- ---------
ssh-userauth [SSH-USERAUTH]
ssh-connection [SSH-CONNECT]
4.8. Authentication Method Names
The Authentication Method Name is used to describe an authentication
method for the "ssh-userauth" service [SSH-USERAUTH]. The following
table identifies the initial assignments of the Authentication Method
Names.
Method Name Reference
------------ ---------
publickey [SSH-USERAUTH, Section 7]
password [SSH-USERAUTH, Section 8]
hostbased [SSH-USERAUTH, Section 9]
none [SSH-USERAUTH, Section 5.2]
4.9. Connection Protocol Assigned Names
The following table lists the initial assignments to the Connection
Protocol Type and Request names.
4.9.1. Connection Protocol Channel Types
The following table lists the initial assignments of the Connection
Protocol Channel Types.
Channel type Reference
------------ ---------
session [SSH-CONNECT, Section 6.1]
x11 [SSH-CONNECT, Section 6.3.2]
forwarded-tcpip [SSH-CONNECT, Section 7.2]
direct-tcpip [SSH-CONNECT, Section 7.2]
4.9.2. Connection Protocol Global Request Names
The following table lists the initial assignments of the Connection
Protocol Global Request Names.
Request type Reference
------------ ---------
tcpip-forward [SSH-CONNECT, Section 7.1]
cancel-tcpip-forward [SSH-CONNECT, Section 7.1]
4.9.3. Connection Protocol Channel Request Names
The following table lists the initial assignments of the Connection
Protocol Channel Request Names.
Request type Reference
------------ ---------
pty-req [SSH-CONNECT, Section 6.2]
x11-req [SSH-CONNECT, Section 6.3.1]
env [SSH-CONNECT, Section 6.4]
shell [SSH-CONNECT, Section 6.5]
exec [SSH-CONNECT, Section 6.5]
subsystem [SSH-CONNECT, Section 6.5]
window-change [SSH-CONNECT, Section 6.7]
xon-xoff [SSH-CONNECT, Section 6.8]
signal [SSH-CONNECT, Section 6.9]
exit-status [SSH-CONNECT, Section 6.10]
exit-signal [SSH-CONNECT, Section 6.10]
4.9.4. Initial Assignment of Signal Names
The following table lists the initial assignments of the Signal
Names.
Signal Reference
------ ---------
ABRT [SSH-CONNECT]
ALRM [SSH-CONNECT]
FPE [SSH-CONNECT]
HUP [SSH-CONNECT]
ILL [SSH-CONNECT]
INT [SSH-CONNECT]
KILL [SSH-CONNECT]
PIPE [SSH-CONNECT]
QUIT [SSH-CONNECT]
SEGV [SSH-CONNECT]
TERM [SSH-CONNECT]
USR1 [SSH-CONNECT]
USR2 [SSH-CONNECT]
4.9.5. Connection Protocol Subsystem Names
There are no initial assignments of the Connection Protocol Subsystem
Names.
4.10. Key Exchange Method Names
The name "diffie-hellman-group1-sha1" is used for a key exchange
method using an Oakley group, as defined in [RFC2409]. SSH maintains
its own group identifier space, which is logically distinct from
Oakley [RFC2412] and IKE; however, for one additional group, the
Working Group adopted the number assigned by [RFC3526], using
"diffie-hellman-group14-sha1" for the name of the second defined
group. Implementations should treat these names as opaque
identifiers and should not assume any relationship between the groups
used by SSH and the groups defined for IKE.
The following table identifies the initial assignments of the key
exchange methods.
Method name Reference
------------ ---------
diffie-hellman-group1-sha1 [SSH-TRANS, Section 8.1]
diffie-hellman-group14-sha1 [SSH-TRANS, Section 8.2]
4.11. Assigned Algorithm Names
4.11.1. Encryption Algorithm Names
The following table identifies the initial assignment of the
Encryption Algorithm Names.
Encryption Algorithm Name Reference
------------------------- ---------
3des-cbc [SSH-TRANS, Section 6.3]
blowfish-cbc [SSH-TRANS, Section 6.3]
twofish256-cbc [SSH-TRANS, Section 6.3]
twofish-cbc [SSH-TRANS, Section 6.3]
twofish192-cbc [SSH-TRANS, Section 6.3]
twofish128-cbc [SSH-TRANS, Section 6.3]
aes256-cbc [SSH-TRANS, Section 6.3]
aes192-cbc [SSH-TRANS, Section 6.3]
aes128-cbc [SSH-TRANS, Section 6.3]
serpent256-cbc [SSH-TRANS, Section 6.3]
serpent192-cbc [SSH-TRANS, Section 6.3]
serpent128-cbc [SSH-TRANS, Section 6.3]
arcfour [SSH-TRANS, Section 6.3]
idea-cbc [SSH-TRANS, Section 6.3]
cast128-cbc [SSH-TRANS, Section 6.3]
none [SSH-TRANS, Section 6.3]
des-cbc [FIPS-46-3] HISTORIC; See
page 4 of [FIPS-46-3]
4.11.2. MAC Algorithm Names
The following table identifies the initial assignments of the MAC
Algorithm Names.
MAC Algorithm Name Reference
------------------ ---------
hmac-sha1 [SSH-TRANS, Section 6.4]
hmac-sha1-96 [SSH-TRANS, Section 6.4]
hmac-md5 [SSH-TRANS, Section 6.4]
hmac-md5-96 [SSH-TRANS, Section 6.4]
none [SSH-TRANS, Section 6.4]
4.11.3. Public Key Algorithm Names
The following table identifies the initial assignments of the Public
Key Algorithm names.
Public Key Algorithm Name Reference
------------------------- ---------
ssh-dss [SSH-TRANS, Section 6.6]
ssh-rsa [SSH-TRANS, Section 6.6]
pgp-sign-rsa [SSH-TRANS, Section 6.6]
pgp-sign-dss [SSH-TRANS, Section 6.6]
4.11.4. Compression Algorithm Names
The following table identifies the initial assignments of the
Compression Algorithm names.
Compression Algorithm Name Reference
-------------------------- ---------
none [SSH-TRANS, Section 6.2]
zlib [SSH-TRANS, Section 6.2]
5. Security Considerations
This protocol provides a secure encrypted channel over an insecure
network.
Full security considerations for this protocol are provided in
[SSH-ARCH].
6. References
6.1. Normative References
[SSH-ARCH] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell
(SSH) Protocol Architecture", RFC 4251, January 2006.
[SSH-TRANS] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell
(SSH) Transport Layer Protocol", RFC 4253, January
2006.
[SSH-USERAUTH] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell
(SSH) Authentication Protocol", RFC 4252, January
2006.
[SSH-CONNECT] Ylonen, T. and C. Lonvick, Ed., "The Secure Shell
(SSH) Connection Protocol", RFC 4254, January 2006.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2409] Harkins, D. and D. Carrel, "The Internet Key Exchange
(IKE)", RFC 2409, November 1998.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing
an IANA Considerations Section in RFCs", BCP 26, RFC
2434, October 1998.
[RFC3526] Kivinen, T. and M. Kojo, "More Modular Exponential
(MODP) Diffie-Hellman groups for Internet Key Exchange
(IKE)", RFC 3526, May 2003.
6.2. Informative References
[RFC0822] Crocker, D., "Standard for the format of ARPA Internet
text messages", STD 11, RFC 822, August 1982.
[RFC1034] Mockapetris, P., "Domain names - concepts and
facilities", STD 13, RFC 1034, November 1987.
[RFC2412] Orman, H., "The OAKLEY Key Determination Protocol",
RFC 2412, November 1998.
[FIPS-46-3] US National Institute of Standards and Technology,
"Data Encryption Standard (DES)", Federal Information
Processing Standards Publication 46-3, October 1999.
Authors' Addresses
Sami Lehtinen
SSH Communications Security Corp
Valimotie 17
00380 Helsinki
Finland
EMail: sjl@ssh.com
Chris Lonvick (editor)
Cisco Systems, Inc.
12515 Research Blvd.
Austin 78759
USA
EMail: clonvick@cisco.com
Trademark Notice
"ssh" is a registered trademark in the United States and/or other
countries.
Full Copyright Statement
Copyright (C) The Internet Society (2006).
This document is subject to the rights, licenses and restrictions
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
This document and the information contained herein are provided on an
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY AND THE INTERNET
ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS OR IMPLIED,
INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE
INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
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Acknowledgement
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AI ELI5
On this page
PROBLEMThe SSH protocol documents use many numbers and names (messages, error codes, algorithms) that need one shared registry and clear rules for adding more.
MECHANISMThis document gives IANA the initial contents of each SSH registry, the naming conventions, and the allocation policy for future entries, such as Standards Action or IETF Consensus, with ranges kept for private use.
STATUS TODAYIt defines no new protocol. It is a Proposed Standard and has been updated by RFC 8268, RFC 9142 and RFC 9519.
§1Purpose and Conventions
This document does not define a new protocol. It creates the initial state of the IANA databases for the SSH protocol and holds the instructions for future assignments. Apart from one HISTORIC algorithm generally regarded as obsolete, it adds nothing that is not already defined in the SSH architecture (RFC 4251), transport (RFC 4253), authentication (RFC 4252) and connection (RFC 4254) documents. Its whole text is the IANA Considerations for SSH.
SSH documents use the RFC 2119 requirement keywords. Namespace allocation words such as PRIVATE USE, FIRST COME FIRST SERVED, EXPERT REVIEW, SPECIFICATION REQUIRED, IESG APPROVAL, IETF CONSENSUS and STANDARDS ACTION follow RFC 2434. The document also fixes a convention: protocol field names appear in single quotes, and example values in double quotes.
This is not a new game. It is the scoreboard that lists the numbers and names the game already uses, and the rules for adding more.
§2Message Numbers
Every SSH packet starts with a one-byte message number that says what the payload is. Numbers run from 1 to 255 and are split into blocks by protocol layer: 1 to 19 for generic transport messages, 20 to 29 for algorithm negotiation, 30 to 49 for key-exchange-specific messages, 50 to 59 for generic user authentication, 60 to 79 for method-specific authentication, 80 to 89 for generic connection messages and 90 to 127 for channel messages. The range 128 to 191 is reserved for client protocols and 192 to 255 is for local extensions.
The initial table assigns, for example, SSH_MSG_DISCONNECT = 1, SSH_MSG_KEXINIT = 20, SSH_MSG_USERAUTH_REQUEST = 50, SSH_MSG_GLOBAL_REQUEST = 80, SSH_MSG_CHANNEL_OPEN = 90 and SSH_MSG_CHANNEL_DATA = 94.
New numbers in 1 to 29, 50 to 59 and 80 to 127 MUST go through STANDARDS ACTION. Numbers 30 to 49 and 60 to 79 are defined by the key exchange or authentication method. Numbers 128 to 191 need IETF CONSENSUS, and IANA does not control 192 to 255, which is PRIVATE USE.
Each kind of message wears a number tag. The numbers are grouped like apartment floors, so a number tells you which part of SSH the message belongs to.
- 1-19Transport generic — Disconnect, ignore, debug and similar messages.
- 20-29Algorithm negotiation — For example KEXINIT (20) and NEWKEYS (21).
- 30-49Key exchange specific — Meaning set by the key exchange method.
- 50-59User authentication generic — Request, failure, success and banner messages.
- 60-79User authentication method specific — Meaning set by the authentication method.
- 80-89Connection protocol generic — Global requests and their replies.
- 90-127Channel related — Open, data, close and requests on a channel.
- 128-191Client protocols — Reserved; assigned by IETF CONSENSUS.
- 192-255Local extensions — PRIVATE USE; IANA does not control it.
§3Reason Codes and Data Types
Three small registries hold 32-bit values. Disconnection reason codes, sent in SSH_MSG_DISCONNECT, run from 1 (SSH_DISCONNECT_HOST_NOT_ALLOWED_TO_CONNECT) to 15 (SSH_DISCONNECT_ILLEGAL_USER_NAME). Channel connection failure codes, sent in SSH_MSG_CHANNEL_OPEN_FAILURE, are 1 to 4, from SSH_OPEN_ADMINISTRATIVELY_PROHIBITED to SSH_OPEN_RESOURCE_SHORTAGE. The extended channel data registry has one entry, SSH_EXTENDED_DATA_STDERR = 1.
For all three, new values MUST be assigned sequentially through IETF CONSENSUS, and IANA will not assign anything from 0xFE000000 to 0xFFFFFFFF, which is left for PRIVATE USE.
For channel failure codes the private range is split in two. 0xFE000000 to 0xFEFFFFFF is for locally assigned channel types, such as one named example_session@example.com. If the server does not understand the channel type, it MUST answer with reason code 3. The range starting with 0xFF has no restrictions and is essentially for experimentation.
When something goes wrong, SSH says why with a code number, like a teacher's list: 1 means not allowed, 2 means broke the rules. A few numbers at the end are saved for people to invent their own.
| Registry | Initial values | IETF CONSENSUS range | PRIVATE USE range |
|---|---|---|---|
| Disconnect reason code | 1 to 15 | 0x00000010 to 0xFDFFFFFF | 0xFE000000 to 0xFFFFFFFF |
| Channel open failure code | 1 to 4 | 0x00000005 to 0xFDFFFFFF | 0xFE000000 to 0xFFFFFFFF |
| Extended data type code | 1 | 0x00000002 to 0xFDFFFFFF | 0xFE000000 to 0xFFFFFFFF |
§4Pseudo-Terminal Modes
A pty-req channel request MUST include an encoded terminal modes value, which is a byte stream of opcode and argument pairs. Opcodes are one byte long. Opcodes 1 to 159 have a uint32 argument, and 160 to 255 are not yet defined.
The initial table maps opcodes to terminal settings that will look familiar from Unix terminals. Opcode 0 (TTY_OP_END) ends the list, 1 is VINTR (the interrupt character), 53 is ECHO (enable echoing), 91 is CS8 (8 bit mode), 128 is TTY_OP_ISPEED and 129 is TTY_OP_OSPEED (input and output baud rate in bits per second). Not all of these characters are supported on all systems. New opcodes MUST be assigned through IETF CONSENSUS.
When you ask for a terminal, you can also send a list of settings, like turning the echo of your typing on. Each setting has its own number.
§5Names and Name Spaces
Many SSH registries use text names instead of numbers. Registered names MUST be printable US-ASCII, MUST NOT contain an at-sign, a comma, whitespace, control characters or DEL, are case-sensitive, and MUST NOT be longer than 64 characters. New names MUST go through IETF CONSENSUS.
Names containing an at-sign are locally extensible and are neither registered nor controlled by IANA. They have the form name@domainname, where the part after the at-sign MUST be a fully qualified domain name controlled by whoever defines the name. The RFC gives ourcipher-cbc@example.com as an example, and notes that the resemblance to email addresses is purely coincidental.
The remaining tables list the initial names. Service names: ssh-userauth and ssh-connection. Authentication methods: publickey, password, hostbased and none. Channel types: session, x11, forwarded-tcpip and direct-tcpip. Global requests: tcpip-forward and cancel-tcpip-forward. There are also channel request names such as pty-req, shell, exec and exit-status, a list of signal names such as INT and TERM, and no initial subsystem names.
Official names have to be short and plain, and a name with an @ and your own website address in it is yours to make up without asking anyone.
§6Key Exchange and Algorithm Names
Key exchange methods start with diffie-hellman-group1-sha1, which uses an Oakley group from RFC 2409, and diffie-hellman-group14-sha1. The RFC says SSH keeps its own group identifier space, so implementations should treat these names as opaque identifiers and not assume a link to the IKE groups.
Encryption algorithm names include 3des-cbc, aes128-cbc, aes192-cbc, aes256-cbc, blowfish-cbc, the Twofish and Serpent families, arcfour, idea-cbc, cast128-cbc and none. The one HISTORIC entry is des-cbc. MAC names are hmac-sha1, hmac-sha1-96, hmac-md5, hmac-md5-96 and none. Public key algorithms are ssh-dss, ssh-rsa, pgp-sign-rsa and pgp-sign-dss. Compression names are none and zlib.
The details of each algorithm are in the transport layer document, RFC 4253. This RFC only fixes the names.
Each locking method SSH can use gets a nickname, so both sides can say which one they want to use.
§7Security Considerations
The section is two sentences. It says the protocol provides a secure encrypted channel over an insecure network, and that full security considerations are in the SSH architecture document, RFC 4251. This registry document adds none of its own.
This list only lists numbers. The safety rules for SSH are in the main SSH book.
§8References
[SSH-ARCH]RFC 4251Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Protocol Architecture", RFC 4251, January 2006.January 2006[SSH-TRANS]RFC 4253Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Transport Layer Protocol", RFC 4253, January 2006.January 2006[SSH-USERAUTH]RFC 4252Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Authentication Protocol", RFC 4252, January 2006.January 2006[SSH-CONNECT]RFC 4254Ylonen, T. and C. Lonvick, Ed., "The Secure Shell (SSH) Connection Protocol", RFC 4254, January 2006.January 2006[RFC2119]RFC 2119Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, March 1997.March 1997[RFC2434]RFC 2434Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.October 1998