draft-ietf-secsh-publickey-subsystem-06.txt   draft-ietf-secsh-publickey-subsystem-07.txt 
Secure Shell Working Group J. Galbraith Secure Shell Working Group J. Galbraith
Internet-Draft J. Van Dyke Internet-Draft J. Van Dyke
Intended status: Informational B. McClure Intended status: Informational B. McClure
Expires: February 1, 2007 VanDyke Software Expires: March 5, 2007 VanDyke Software
J. Bright J. Bright
Silicon Circus Silicon Circus
July 31, 2006 September 1, 2006
Secure Shell Public-Key Subsystem Secure Shell Public-Key Subsystem
draft-ietf-secsh-publickey-subsystem-06.txt draft-ietf-secsh-publickey-subsystem-07.txt
Status of this Memo Status of this Memo
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This Internet-Draft will expire on February 1, 2007. This Internet-Draft will expire on March 5, 2007.
Copyright Notice Copyright Notice
Copyright (C) The Internet Society (2006). Copyright (C) The Internet Society (2006).
Abstract Abstract
Secure Shell defines an authentication mechanism that is based on Secure Shell defines an authentication mechanism that is based on
public keys, but does not define any mechanism for key distribution. public keys, but does not define any mechanism for key distribution.
No common key management solution exists in current implementations. No common key management solution exists in current implementations.
This document describes a protocol that can be used to configure This document describes a protocol that can be used to configure
public keys in an implementation-independent fashion, allowing client public keys in an implementation-independent fashion, allowing client
software to take on the burden of this configuration. software to take on the burden of this configuration.
This protocol is intended to be used from the Secure Shell Connection
Protocol [4] as a subsystem, as described in the section "Starting a
Shell or a Command". The subsystem name used with this protocol is
"publickey".
The public-key subsystem provides a server-independent mechanism for The public-key subsystem provides a server-independent mechanism for
clients to add public keys, remove public keys, and list the current clients to add public keys, remove public keys, and list the current
public keys known by the server. Rights to manage public keys are public keys known by the server. Rights to manage public keys are
specific and limited to the authenticated user. specific and limited to the authenticated user.
A public key may also be associated with various restrictions, A public key may also be associated with various restrictions,
including a mandatory command or subsystem. including a mandatory command or subsystem.
Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Public-Key Subsystem Overview . . . . . . . . . . . . . . . . 5 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 5
2.1. Opening the Public-Key Subsystem . . . . . . . . . . . . . 5 3. Public-Key Subsystem Overview . . . . . . . . . . . . . . . . 6
2.2. Requests and Responses . . . . . . . . . . . . . . . . . . 6 3.1. Opening the Public-Key Subsystem . . . . . . . . . . . . . 6
2.3. The Status Message . . . . . . . . . . . . . . . . . . . . 6 3.2. Requests and Responses . . . . . . . . . . . . . . . . . . 7
2.3.1. Status Codes . . . . . . . . . . . . . . . . . . . . . 6 3.3. The Status Message . . . . . . . . . . . . . . . . . . . . 7
2.4. The Version Packet . . . . . . . . . . . . . . . . . . . . 7 3.3.1. Status Codes . . . . . . . . . . . . . . . . . . . . . 7
3. Public-Key Subsystem Operations . . . . . . . . . . . . . . . 8 3.4. The Version Packet . . . . . . . . . . . . . . . . . . . . 8
3.1. Adding a Public Key . . . . . . . . . . . . . . . . . . . 8 4. Public-Key Subsystem Operations . . . . . . . . . . . . . . . 9
3.2. Removing a Public Key . . . . . . . . . . . . . . . . . . 11 4.1. Adding a Public Key . . . . . . . . . . . . . . . . . . . 9
3.3. Listing Public Keys . . . . . . . . . . . . . . . . . . . 11 4.2. Removing a Public Key . . . . . . . . . . . . . . . . . . 12
3.4. Listing Server Capabilities . . . . . . . . . . . . . . . 11 4.3. Listing Public Keys . . . . . . . . . . . . . . . . . . . 12
4. Security Considerations . . . . . . . . . . . . . . . . . . . 13 4.4. Listing Server Capabilities . . . . . . . . . . . . . . . 12
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14 5. Security Considerations . . . . . . . . . . . . . . . . . . . 14
5.1. Registrations . . . . . . . . . . . . . . . . . . . . . . 14 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
5.2. Names . . . . . . . . . . . . . . . . . . . . . . . . . . 14 6.1. Registrations . . . . . . . . . . . . . . . . . . . . . . 15
5.2.1. Conventions for Names . . . . . . . . . . . . . . . . 14 6.2. Names . . . . . . . . . . . . . . . . . . . . . . . . . . 15
5.2.2. Future Assignments of Names . . . . . . . . . . . . . 15 6.2.1. Conventions for Names . . . . . . . . . . . . . . . . 15
5.3. Request Names . . . . . . . . . . . . . . . . . . . . . . 15 6.2.2. Future Assignments of Names . . . . . . . . . . . . . 16
5.4. Response Names . . . . . . . . . . . . . . . . . . . . . . 15 6.3. Request Names . . . . . . . . . . . . . . . . . . . . . . 16
5.5. Attribute Names . . . . . . . . . . . . . . . . . . . . . 15 6.4. Response Names . . . . . . . . . . . . . . . . . . . . . . 16
5.6. Status Codes . . . . . . . . . . . . . . . . . . . . . . . 16 6.5. Attribute Names . . . . . . . . . . . . . . . . . . . . . 16
5.6.1. Conventions . . . . . . . . . . . . . . . . . . . . . 16 6.6. Status Codes . . . . . . . . . . . . . . . . . . . . . . . 17
5.6.2. Initial Assignments . . . . . . . . . . . . . . . . . 16 6.6.1. Conventions . . . . . . . . . . . . . . . . . . . . . 17
5.6.3. Future Assignments . . . . . . . . . . . . . . . . . . 16 6.6.2. Initial Assignments . . . . . . . . . . . . . . . . . 17
6. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17 6.6.3. Future Assignments . . . . . . . . . . . . . . . . . . 17
6.1. Normative References . . . . . . . . . . . . . . . . . . . 17 7. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
6.2. Informative References . . . . . . . . . . . . . . . . . . 17 7.1. Normative References . . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 7.2. Informative References . . . . . . . . . . . . . . . . . . 18
Intellectual Property and Copyright Statements . . . . . . . . . . 19 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
Intellectual Property and Copyright Statements . . . . . . . . . . 20
1. Introduction 1. Introduction
Secure Shell is a protocol for secure remote login and other secure Secure Shell is a protocol for secure remote login and other secure
network services over an insecure network. Secure Shell defines an network services over an insecure network. Secure Shell defines an
authentication mechanism that is based on public keys, but does not authentication mechanism that is based on public keys, but does not
define any mechanism for key distribution. Common practice is to define any mechanism for key distribution. Common practice is to
authenticate once with password authentication and transfer the authenticate once with password authentication and transfer the
public key to the server. However, to date no two implementations public key to the server. However, to date no two implementations
use the same mechanism to configure a public key for use. use the same mechanism to configure a public key for use.
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in implementation. It is not intended as a PKIX replacement. in implementation. It is not intended as a PKIX replacement.
The Secure Shell Public-Key subsystem has been designed to run on top The Secure Shell Public-Key subsystem has been designed to run on top
of the Secure Shell transport layer [2] and user authentication of the Secure Shell transport layer [2] and user authentication
protocols [3]. It provides a simple mechanism for the client to protocols [3]. It provides a simple mechanism for the client to
manage public keys on the server. manage public keys on the server.
This document should be read only after reading the Secure Shell This document should be read only after reading the Secure Shell
architecture [1] and Secure Shell connection [4] documents. architecture [1] and Secure Shell connection [4] documents.
This protocol is intended to be used from the Secure Shell Connection
Protocol [4] as a subsystem, as described in the section "Starting a
Shell or a Command". The subsystem name used with this protocol is
"publickey".
This protocol requires that the user be able to authenticate in some This protocol requires that the user be able to authenticate in some
fashion before it can be used. If password authentication is used, fashion before it can be used. If password authentication is used,
servers SHOULD provide a configuration option to disable the use of servers SHOULD provide a configuration option to disable the use of
password authentication after the first public key is added. password authentication after the first public key is added.
2. Public-Key Subsystem Overview 2. Terminology
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 [5].
3. Public-Key Subsystem Overview
The public-key subsystem provides a server-independent mechanism for The public-key subsystem provides a server-independent mechanism for
clients to add public keys, remove public keys, and list the current clients to add public keys, remove public keys, and list the current
public keys known by the server. The subsystem name is "publickey". public keys known by the server. The subsystem name is "publickey".
The public keys added, removed, and listed using this protocol are The public keys added, removed, and listed using this protocol are
specific and limited to those of the authenticated user. specific and limited to those of the authenticated user.
The operations to add, remove, and list the authenticated user's The operations to add, remove, and list the authenticated user's
public keys are performed as request packets sent to the server. The public keys are performed as request packets sent to the server. The
server sends response packets that indicate success or failure as server sends response packets that indicate success or failure as
well as provide specific response data. well as provide specific response data.
The format of public-key blobs are detailed in the SSH Transport The format of public-key blobs are detailed in section 6.6, "Public
Protocol document [2]. Key Algorithms" of the SSH Transport Protocol document [2].
2.1. Opening the Public-Key Subsystem 3.1. Opening the Public-Key Subsystem
The public-key subsystem is started by a client sending an The public-key subsystem is started by a client sending an
SSH_MSG_CHANNEL_REQUEST over an existing session's channel. SSH_MSG_CHANNEL_REQUEST over an existing session's channel.
The details of how a session is opened are described in the SSH The details of how a session is opened are described in the SSH
Connection Protocol document [4] in the section "Opening a Session". Connection Protocol document [4] in the section "Opening a Session".
To open the public-key subsystem, the client sends: To open the public-key subsystem, the client sends:
byte SSH_MSG_CHANNEL_REQUEST byte SSH_MSG_CHANNEL_REQUEST
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started or SSH_MSG_CHANNEL_FAILURE if the server failed to start or started or SSH_MSG_CHANNEL_FAILURE if the server failed to start or
does not support the public-key subsystem. does not support the public-key subsystem.
The server SHOULD respond with SSH_MSG_CHANNEL_FAILURE if the user is The server SHOULD respond with SSH_MSG_CHANNEL_FAILURE if the user is
not allowed access to the public-key subsystem (for example, because not allowed access to the public-key subsystem (for example, because
the user authenticated with a restricted public key). the user authenticated with a restricted public key).
It is RECOMMENDED that clients request and check the reply for this It is RECOMMENDED that clients request and check the reply for this
request. request.
2.2. Requests and Responses 3.2. Requests and Responses
All public-key subsystem requests and responses are sent in the All public-key subsystem requests and responses are sent in the
following form: following form:
uint32 length uint32 length
string name string name
... request/response specific data follows ... request/response specific data follows
The length field describes the length of the name field and of the The length field describes the length of the name field and of the
request/response-specific data, but does not include the length of request/response-specific data, but does not include the length of
the length field itself. The client MUST receive acknowledgement of the length field itself. The client MUST receive acknowledgement of
each request prior to sending a new request. each request prior to sending a new request.
The version packet, as well as all requests and responses described The version packet, as well as all requests and responses described
in Section 3, are a description of the 'name' field and the data part in Section 4, are a description of the 'name' field and the data part
of the packet. of the packet.
2.3. The Status Message 3.3. The Status Message
A request is acknowledged by sending a status packet. If there is A request is acknowledged by sending a status packet. If there is
data in response to the request, the status packet is sent after all data in response to the request, the status packet is sent after all
data has been sent. data has been sent.
string "status" string "status"
uint32 status code uint32 status code
string description [RFC-2279] string description [RFC-3629]
string language tag [RFC-1766] string language tag [RFC-3066]
A status message MUST be sent for any unrecognized packets, and the A status message MUST be sent for any unrecognized packets, and the
request SHOULD NOT close the subsystem. request SHOULD NOT close the subsystem.
2.3.1. Status Codes 3.3.1. Status Codes
The status code gives the status in a more machine-readable format The status code gives the status in a more machine-readable format
(suitable for localization), and can have the following values: (suitable for localization), and can have the following values:
SSH_PUBLICKEY_SUCCESS 0 SSH_PUBLICKEY_SUCCESS 0
SSH_PUBLICKEY_ACCESS_DENIED 1 SSH_PUBLICKEY_ACCESS_DENIED 1
SSH_PUBLICKEY_STORAGE_EXCEEDED 2 SSH_PUBLICKEY_STORAGE_EXCEEDED 2
SSH_PUBLICKEY_VERSION_NOT_SUPPORTED 3 SSH_PUBLICKEY_VERSION_NOT_SUPPORTED 3
SSH_PUBLICKEY_KEY_NOT_FOUND 4 SSH_PUBLICKEY_KEY_NOT_FOUND 4
SSH_PUBLICKEY_KEY_NOT_SUPPORTED 5 SSH_PUBLICKEY_KEY_NOT_SUPPORTED 5
SSH_PUBLICKEY_KEY_ALREADY_PRESENT 6 SSH_PUBLICKEY_KEY_ALREADY_PRESENT 6
SSH_PUBLICKEY_GENERAL_FAILURE 7 SSH_PUBLICKEY_GENERAL_FAILURE 7
SSH_PUBLICKEY_REQUEST_NOT_SUPPORTED 8 SSH_PUBLICKEY_REQUEST_NOT_SUPPORTED 8
SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED 9 SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED 9
If a request completed successfully, the server MUST send the status If a request completed successfully, the server MUST send the status
code SSH_PUBLICKEY_SUCCESS. The meaning of the failure codes is as code SSH_PUBLICKEY_SUCCESS. The meaning of the failure codes is as
implied by their names. implied by their names.
2.4. The Version Packet 3.4. The Version Packet
Both sides MUST start by sending a version packet that indicates the Both sides MUST start by sending a version packet that indicates the
version of the protocol they are using. version of the protocol they are using.
string "version" string "version"
uint32 protocol-version-number uint32 protocol-version-number
This document describes version 2 of the protocol. This document describes version 2 of the protocol.
Both sides send the highest version that they implement. The lower Both sides send the highest version that they implement. The lower
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status message with the status SSH_PUBLICKEY_VERSION_NOT_SUPPORTED status message with the status SSH_PUBLICKEY_VERSION_NOT_SUPPORTED
SHOULD be sent. Note that, normally, status messages are only sent SHOULD be sent. Note that, normally, status messages are only sent
by the server (in response to requests from the client). This is the by the server (in response to requests from the client). This is the
only occasion on which the client sends a status message. only occasion on which the client sends a status message.
Both sides MUST wait to receive this version before continuing. The Both sides MUST wait to receive this version before continuing. The
"version" packet MUST NOT be sent again after this initial exchange. "version" packet MUST NOT be sent again after this initial exchange.
The SSH_PUBLICKEY_VERSION_NOT_SUPPORTED status code must not be sent The SSH_PUBLICKEY_VERSION_NOT_SUPPORTED status code must not be sent
in response to any other request. in response to any other request.
3. Public-Key Subsystem Operations Implementations MAY use the first 15 bytes of the version packet as a
"magic cookie" to avoid processing spurious output from the user's
shell (as described in section 6.5 of [4]). These bytes will always
be:
0x00 0x00 0x00 0x0F 0x00 0x00 0x00 0x07 0x76 0x65 0x72 0x73 0x69 0x6F
0x6E
4. Public-Key Subsystem Operations
The public-key subsystem currently defines four operations: add, The public-key subsystem currently defines four operations: add,
remove, list, and listattributes. remove, list, and listattributes.
3.1. Adding a Public Key 4.1. Adding a Public Key
If the client wishes to add a public key, the client sends: If the client wishes to add a public key, the client sends:
string "add" string "add"
string public-key algorithm name string public-key algorithm name
string public-key blob string public-key blob
boolean overwrite boolean overwrite
uint32 attribute-count uint32 attribute-count
string attrib-name string attrib-name
string attrib-value string attrib-value
bool mandatory bool critical
repeated attribute-count times repeated attribute-count times
The server MUST attempt to store the public key for the user in the The server MUST attempt to store the public key for the user in the
appropriate location so the public key can be used for subsequent appropriate location so the public key can be used for subsequent
public-key authentications. If the overwrite field is false and the public-key authentications. If the overwrite field is false and the
specified key already exists, the server MUST return specified key already exists, the server MUST return
SSH_PUBLICKEY_KEY_ALREADY_PRESENT. If the server returns this, the SSH_PUBLICKEY_KEY_ALREADY_PRESENT. If the server returns this, the
client SHOULD provide an option to the user to overwrite the key. If client SHOULD provide an option to the user to overwrite the key. If
the overwrite field is true and the specified key already exists, but the overwrite field is true and the specified key already exists, but
cannot be overwritten, the server MUST return cannot be overwritten, the server MUST return
SSH_PUBLICKEY_ACCESS_DENIED. SSH_PUBLICKEY_ACCESS_DENIED.
Attribute names are defined following the same scheme laid out for Attribute names are defined following the same scheme laid out for
algorithm names in [1]. If the server does not implement a mandatory algorithm names in [1]. If the server does not implement a critical
attribute, it MUST fail the add, with the status code attribute, it MUST fail the add, with the status code
SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED. For the purposes of a SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED. For the purposes of a
mandatory attribute, mere storage of the attribute is not sufficient critical attribute, mere storage of the attribute is not sufficient
-- rather, the server must understand and implement the intent of the -- rather, the server must understand and implement the intent of the
attribute. attribute.
The following attributes are currently defined: The following attributes are currently defined:
"comment" "comment"
The value of the comment attribute contains user-specified text about The value of the comment attribute contains user-specified text about
the public key. The server SHOULD make every effort to preserve this the public key. The server SHOULD make every effort to preserve this
value and return it with the key during any subsequent list value and return it with the key during any subsequent list
operation. The server MUST NOT attempt to interpret or act upon the operation. The server MUST NOT attempt to interpret or act upon the
content of the comment field in any way. The comment attribute must content of the comment field in any way. The comment attribute must
be specified in UTF-8 format [6]. be specified in UTF-8 format [7].
The comment field is useful so the user can identify the key without The comment field is useful so the user can identify the key without
resorting to comparing its fingerprint. This attribute SHOULD NOT be resorting to comparing its fingerprint. This attribute SHOULD NOT be
mandatory. critical.
"comment-language" "comment-language"
If this attribute is specified, it MUST immediately follow a If this attribute is specified, it MUST immediately follow a
"comment" attribute and specify the language for that attribute [5]. "comment" attribute and specify the language for that attribute [6].
The client MAY specify more than one comment if it additionally The client MAY specify more than one comment if it additionally
specifies a different language for each of those comments. The specifies a different language for each of those comments. The
server SHOULD attempt to store each comment with its language server SHOULD attempt to store each comment with its language
attribute. This attribute SHOULD NOT be mandatory. attribute. This attribute SHOULD NOT be critical.
"command-override" "command-override"
"command-override" specifies a command to be executed when this key "command-override" specifies a command to be executed when this key
is in use. The command should be executed by the server when it is in use. The command should be executed by the server when it
receives an "exec" or "shell" request from the client, in place of receives an "exec" or "shell" request from the client, in place of
the command or shell which would otherwise have been executed as a the command or shell which would otherwise have been executed as a
result of that request. If the command string is empty, both "exec" result of that request. If the command string is empty, both "exec"
and "shell" requests should be denied. If no "command-override" and "shell" requests should be denied. If no "command-override"
attribute is specified, all "exec" and "shell" requests should be attribute is specified, all "exec" and "shell" requests should be
permitted (as long as they satisfy other security or authorization permitted (as long as they satisfy other security or authorization
checks the server may perform). This attribute SHOULD be mandatory. checks the server may perform). This attribute SHOULD be critical.
"subsystem" "subsystem"
"subsystem" specifies a comma-separated list of subsystems that may "subsystem" specifies a comma-separated list of subsystems that may
be started (using a "subsystem" request) when this key is in use. be started (using a "subsystem" request) when this key is in use.
This attribute SHOULD be mandatory. If the value is empty, no This attribute SHOULD be critical. If the value is empty, no
subsystems may be started. If the "subsystem" attribute is not subsystems may be started. If the "subsystem" attribute is not
specified, no restrictions are placed on which subsystems may be specified, no restrictions are placed on which subsystems may be
started when authenticated using this key. started when authenticated using this key.
"x11" "x11"
"x11" specifies that X11 forwarding may not be performed when this "x11" specifies that X11 forwarding may not be performed when this
key is in use. The attribute-value field SHOULD be empty for this key is in use. The attribute-value field SHOULD be empty for this
attribute. This attribute SHOULD be mandatory. attribute. This attribute SHOULD be critical.
"shell" "shell"
"shell" specifies that session channel "shell" requests should be "shell" specifies that session channel "shell" requests should be
denied when this key is in use. The attribute-value field SHOULD be denied when this key is in use. The attribute-value field SHOULD be
empty for this attribute. This attribute SHOULD be mandatory. empty for this attribute. This attribute SHOULD be critical.
"exec" "exec"
"exec" specifies that session channel "exec" requests should be "exec" specifies that session channel "exec" requests should be
denied when this key is in use. The attribute-value field SHOULD be denied when this key is in use. The attribute-value field SHOULD be
empty for this attribute. This attribute SHOULD be mandatory. empty for this attribute. This attribute SHOULD be critical.
"agent" "agent"
"agent" specifies that session channel "auth-agent-req" requests "agent" specifies that session channel "auth-agent-req" requests
should be denied when this key is in use. The attribute-value field should be denied when this key is in use. The attribute-value field
SHOULD be empty for this attribute. This attribute SHOULD be SHOULD be empty for this attribute. This attribute SHOULD be
mandatory. critical.
"env" "env"
"env" specifies that session channel "env" requests should be denied "env" specifies that session channel "env" requests should be denied
when this key is in use. The attribute-value field SHOULD be empty when this key is in use. The attribute-value field SHOULD be empty
for this attribute. This attribute SHOULD be mandatory. for this attribute. This attribute SHOULD be critical.
"from" "from"
"from" specifies a comma-separated list of hosts from which the key "from" specifies a comma-separated list of hosts from which the key
may be used. If a host not in this list attempts to use this key for may be used. If a host not in this list attempts to use this key for
authorization purposes, the authorization attempt MUST be denied. authorization purposes, the authorization attempt MUST be denied.
The server SHOULD make a log entry regarding this. The server MAY The server SHOULD make a log entry regarding this. The server MAY
provide a method for administrators to disallow the appearance of a provide a method for administrators to disallow the appearance of a
host in this list. host in this list. The server should use whatever method is
appropriate for its platform to identify the host - e.g. for IP-based
networks, checking the IP address or performing a reverse DNS lookup.
"port-forward" "port-forward"
"port-forward" specifies that no "direct-tcpip" requests should be "port-forward" specifies that no "direct-tcpip" requests should be
accepted, except those to hosts specified in the comma-separated list accepted, except those to hosts specified in the comma-separated list
supplied as a value to this attribute. If the value of this supplied as a value to this attribute. If the value of this
attribute is empty, all "direct-tcpip" requests should be refused attribute is empty, all "direct-tcpip" requests should be refused
when using this key. This attribute SHOULD be mandatory. when using this key. This attribute SHOULD be critical.
"reverse-forward" "reverse-forward"
"reverse-forward" specifies that no "tcpip-forward" requests should "reverse-forward" specifies that no "tcpip-forward" requests should
be accepted, except for the port numbers in the comma-separated list be accepted, except for the port numbers in the comma-separated list
supplied as a value to this attribute. If the value of this supplied as a value to this attribute. If the value of this
attribute is empty, all "tcpip-forward" requests should be refused attribute is empty, all "tcpip-forward" requests should be refused
when using this key. This attribute SHOULD be mandatory. when using this key. This attribute SHOULD be critical.
In addition to the attributes specified by the client, the server MAY In addition to the attributes specified by the client, the server MAY
provide a method for administrators to enforce certain attributes provide a method for administrators to enforce certain attributes
compulsorily. compulsorily.
3.2. Removing a Public Key 4.2. Removing a Public Key
If the client wishes to remove a public key, the client sends: If the client wishes to remove a public key, the client sends:
string "remove" string "remove"
string public-key algorithm name string public-key algorithm name
string public-key blob string public-key blob
The server MUST attempt to remove the public key for the user from The server MUST attempt to remove the public key for the user from
the appropriate location, so that the public key cannot be used for the appropriate location, so that the public key cannot be used for
subsequent authentications. subsequent authentications.
3.3. Listing Public Keys 4.3. Listing Public Keys
If the client wishes to list the known public keys, the client sends: If the client wishes to list the known public keys, the client sends:
string "list" string "list"
The server will respond with zero or more of the following responses: The server will respond with zero or more of the following responses:
string "publickey" string "publickey"
string public-key algorithm name string public-key algorithm name
string public-key blob string public-key blob
uint32 attribute-count uint32 attribute-count
string attrib-name string attrib-name
string attrib-value string attrib-value
repeated attribute-count times repeated attribute-count times
Following the last "publickey" response, a status packet MUST be Following the last "publickey" response, a status packet MUST be
sent. sent.
An implementation MAY choose not to support this request. An implementation MAY choose not to support this request.
3.4. Listing Server Capabilities 4.4. Listing Server Capabilities
If the client wishes to know which key attributes the server If the client wishes to know which key attributes the server
supports, it sends: supports, it sends:
string "listattributes" string "listattributes"
The server will respond with zero or more of the following responses: The server will respond with zero or more of the following responses:
string "attribute" string "attribute"
string attribute name string attribute name
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the "shell" attribute, with "compulsory" marked true. Whatever the "shell" attribute, with "compulsory" marked true. Whatever
attributes the user subsequently asked the server to apply to their attributes the user subsequently asked the server to apply to their
key, the server would also apply the "shell" attribute, rendering it key, the server would also apply the "shell" attribute, rendering it
impossible for the user to use a shell. impossible for the user to use a shell.
Following the last "attribute" response, a status packet MUST be Following the last "attribute" response, a status packet MUST be
sent. sent.
An implementation MAY choose not to support this request. An implementation MAY choose not to support this request.
4. Security Considerations 5. Security Considerations
This protocol assumes that it is run over a secure channel and that This protocol assumes that it is run over a secure channel and that
the endpoints of the channel have been authenticated. Thus, this the endpoints of the channel have been authenticated. Thus, this
protocol assumes that it is externally protected from network-level protocol assumes that it is externally protected from network-level
attacks. attacks.
This protocol provides a mechanism that allows client authentication This protocol provides a mechanism that allows client authentication
data to be uploaded and manipulated. It is the responsibility of the data to be uploaded and manipulated. It is the responsibility of the
server implementation to enforce any access controls that may be server implementation to enforce any access controls that may be
required to limit the access allowed for any particular user (the required to limit the access allowed for any particular user (the
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for the new key than were previously present. Servers should take for the new key than were previously present. Servers should take
care that when doing this, clients are not able to override presets care that when doing this, clients are not able to override presets
from the server's administrator. from the server's administrator.
This protocol requires the client to assume that the server will This protocol requires the client to assume that the server will
correctly implement and observe attributes applied to keys. correctly implement and observe attributes applied to keys.
Implementation errors in the server could cause clients to authorize Implementation errors in the server could cause clients to authorize
keys for access they were not intended to have, or to apply fewer keys for access they were not intended to have, or to apply fewer
restrictions than were intended. restrictions than were intended.
5. IANA Considerations 6. IANA Considerations
This section contains conventions used in naming the namespaces, the This section contains conventions used in naming the namespaces, the
initial state of the registry, and instructions for future initial state of the registry, and instructions for future
assignments. assignments.
5.1. Registrations 6.1. Registrations
Consistent with Section 7 of [1], this document makes the following Consistent with Section 7 of [1], this document makes the following
registration: registration:
The subsystem name "publickey". The subsystem name "publickey".
5.2. Names 6.2. Names
In the following sections, the values for the namespaces are textual. In the following sections, the values for the namespaces are textual.
The conventions and instructions to the IANA for future assignments The conventions and instructions to the IANA for future assignments
are given in this section. The initial assignments are given in are given in this section. The initial assignments are given in
their respective sections. their respective sections.
5.2.1. Conventions for Names 6.2.1. Conventions for Names
All names registered by the IANA in the following sections MUST be All names registered by the IANA in the following sections MUST be
printable US-ASCII strings, and MUST NOT contain the characters at- printable US-ASCII strings, and MUST NOT contain the characters at-
sign ("@"), comma (","), or whitespace or control characters (ASCII sign ("@"), comma (","), or whitespace or control characters (ASCII
codes 32 or less). Names are case-sensitive, and MUST NOT be longer codes 32 or less). Names are case-sensitive, and MUST NOT be longer
than 64 characters. than 64 characters.
A provision is made here for locally extensible names. The IANA will 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. 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 Names with the at-sign in them will have the format of
"name@domainname" (without the double quotes) where the part "name@domainname" (without the double quotes) where the part
preceeding the at-sign is the name. The format of the part preceding preceeding the at-sign is the name. The format of the part preceding
the at-sign is not specified, however these names MUST be printable the at-sign is not specified, however these names MUST be printable
US-ASCII strings, and MUST NOT contain the comma character (","), or US-ASCII strings, and MUST NOT contain the comma character (","), or
whitespace, or control characters (ASCII codes 32 or less). The part whitespace, or control characters (ASCII codes 32 or less). The part
following the at-sign MUST be a valid, fully qualified Internet following the at-sign MUST be a valid, fully qualified Internet
domain name [8] controlled by the person or organization defining the domain name [9] controlled by the person or organization defining the
name. Names are case-sensitive, and MUST NOT be longer than 64 name. Names are case-sensitive, and MUST NOT be longer than 64
characters. It is up to each domain how it manages its local characters. It is up to each domain how it manages its local
namespace. It has been noted that these names resemble STD 11 [7] namespace. It has been noted that these names resemble STD 11 [8]
email addresses. This is purely coincidental and actually has email addresses. This is purely coincidental and actually has
nothing to do with STD 11 [7]. An example of a locally defined name nothing to do with STD 11 [8]. An example of a locally defined name
is "ourcipher-cbc@example.com" (without the double quotes). is "ourcipher-cbc@example.com" (without the double quotes).
5.2.2. Future Assignments of Names 6.2.2. Future Assignments of Names
Requests for assignments of new Names MUST be done through the IETF Requests for assignments of new Names MUST be done through the IETF
Consensus method as described in [9]. Consensus method as described in [10].
5.3. Request Names 6.3. Request Names
The following table lists the initial assignments of Request names. The following table lists the initial assignments of Request names.
Request Name Request Name
------------- -------------
version version
add add
remove remove
list list
listattributes listattributes
5.4. Response Names 6.4. Response Names
The following table lists the initial assignments of Response names. The following table lists the initial assignments of Response names.
Response Name Response Name
-------------- --------------
version version
status status
publickey publickey
attribute attribute
5.5. Attribute Names 6.5. Attribute Names
Attributes are used to define properties or restrictions for public Attributes are used to define properties or restrictions for public
keys. The following table lists the initial assignments of Attribute keys. The following table lists the initial assignments of Attribute
names. names.
Attribute Name Attribute Name
--------------- ---------------
comment comment
comment-language comment-language
command-override command-override
subsystem subsystem
x11 x11
shell shell
exec exec
agent agent
env env
from from
port-forward port-forward
reverse-forward reverse-forward
5.6. Status Codes 6.6. Status Codes
The status code is a byte value, describing the status of a request. The status code is a byte value, describing the status of a request.
5.6.1. Conventions 6.6.1. Conventions
Status responses have status codes in the range 0 to 255. These Status responses have status codes in the range 0 to 255. These
numbers are allocated as follows. Of these, the range 192 to 255 is numbers are allocated as follows. Of these, the range 192 to 255 is
reserved for use by local, private extensions. reserved for use by local, private extensions.
5.6.2. Initial Assignments 6.6.2. Initial Assignments
The following table identifies the initial assignments of the status The following table identifies the initial assignments of the status
code values. code values.
Status code Value Reference Status code Value Reference
------------ ----- --------- ------------ ----- ---------
SSH_PUBLICKEY_SUCCESS 0 SSH_PUBLICKEY_SUCCESS 0
SSH_PUBLICKEY_ACCESS_DENIED 1 SSH_PUBLICKEY_ACCESS_DENIED 1
SSH_PUBLICKEY_STORAGE_EXCEEDED 2 SSH_PUBLICKEY_STORAGE_EXCEEDED 2
SSH_PUBLICKEY_VERSION_NOT_SUPPORTED 3 SSH_PUBLICKEY_VERSION_NOT_SUPPORTED 3
SSH_PUBLICKEY_KEY_NOT_FOUND 4 SSH_PUBLICKEY_KEY_NOT_FOUND 4
SSH_PUBLICKEY_KEY_NOT_SUPPORTED 5 SSH_PUBLICKEY_KEY_NOT_SUPPORTED 5
SSH_PUBLICKEY_KEY_ALREADY_PRESENT 6 SSH_PUBLICKEY_KEY_ALREADY_PRESENT 6
SSH_PUBLICKEY_GENERAL_FAILURE 7 SSH_PUBLICKEY_GENERAL_FAILURE 7
SSH_PUBLICKEY_REQUEST_NOT_SUPPORTED 8 SSH_PUBLICKEY_REQUEST_NOT_SUPPORTED 8
SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED 9 SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED 9
5.6.3. Future Assignments 6.6.3. Future Assignments
Requests for assignments of new message numbers in the range of 0 to Requests for assignments of new message numbers in the range of 0 to
191 MUST be done through the Standards Action method as described in 191 MUST be done through the Standards Action method as described in
[9]. [10].
The IANA will not control the message numbers range of 192 through The IANA will not control the message numbers range of 192 through
255. This range will be left for private use. 255. This range will be left for private use.
6. References 7. References
6.1. Normative References 7.1. Normative References
[1] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol [1] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol
Architecture", RFC 4251, January 2006. Architecture", RFC 4251, January 2006.
[2] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport [2] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport
Layer Protocol", RFC 4253, January 2006. Layer Protocol", RFC 4253, January 2006.
[3] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) [3] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
Authentication Protocol", RFC 4252, January 2006. Authentication Protocol", RFC 4252, January 2006.
[4] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Connection [4] Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Connection
Protocol", RFC 4254, January 2006. Protocol", RFC 4254, January 2006.
[5] Alvestrand, H., "Tags for the Identification of Languages", [5] Bradner, S., "Key words for use in RFCs to Indicate Requirement
RFC 1766, March 1995. Levels", BCP 14, RFC 2119, March 1997.
[6] Yergeau, F., "UTF-8, a transformation format of ISO 10646", [6] Alvestrand, H., "Tags for the Identification of Languages",
RFC 2279, January 1998. BCP 47, RFC 3066, January 2001.
6.2. Informative References [7] Yergeau, F., "UTF-8, a transformation format of ISO 10646",
STD 63, RFC 3629, November 2003.
[7] Crocker, D., "Standard for the format of ARPA Internet text 7.2. Informative References
[8] Crocker, D., "Standard for the format of ARPA Internet text
messages", STD 11, RFC 822, August 1982. messages", STD 11, RFC 822, August 1982.
[8] Mockapetris, P., "Domain names - concepts and facilities", [9] Mockapetris, P., "Domain names - concepts and facilities",
STD 13, RFC 1034, November 1987. STD 13, RFC 1034, November 1987.
[9] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [10] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 2434, October 1998. Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
Authors' Addresses Authors' Addresses
Joseph Galbraith Joseph Galbraith
VanDyke Software VanDyke Software
4848 Tramway Ridge Blvd 4848 Tramway Ridge Blvd
Suite 101 Suite 101
Albuquerque, NM 87111 Albuquerque, NM 87111
US US
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