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rfc:rfc4819

Network Working Group J. Galbraith Request for Comments: 4819 J. Van Dyke Category: Standards Track VanDyke Software

                                                             J. Bright
                                                        Silicon Circus
                                                            March 2007
                 Secure Shell Public Key Subsystem

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 IETF Trust (2007).

Abstract

 Secure Shell defines a user authentication mechanism that is based on
 public keys, but does not define any mechanism for key distribution.
 No common key management solution exists in current implementations.
 This document describes a protocol that can be used to configure
 public keys in an implementation-independent fashion, allowing client
 software to take on the burden of this configuration.
 The Public Key Subsystem provides a server-independent mechanism for
 clients to add public keys, remove public keys, and list the current
 public keys known by the server.  Rights to manage public keys are
 specific and limited to the authenticated user.
 A public key may also be associated with various restrictions,
 including a mandatory command or subsystem.

Galbraith, et al. Standards Track [Page 1] RFC 4819 Secure Shell Public Key Subsystem March 2007

Table of Contents

 1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
 2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
 3.  Public Key Subsystem Overview  . . . . . . . . . . . . . . . .  3
   3.1.  Opening the Public Key Subsystem . . . . . . . . . . . . .  4
   3.2.  Requests and Responses . . . . . . . . . . . . . . . . . .  5
   3.3.  The Status Message . . . . . . . . . . . . . . . . . . . .  5
     3.3.1.  Status Codes . . . . . . . . . . . . . . . . . . . . .  5
   3.4.  The Version Packet . . . . . . . . . . . . . . . . . . . .  6
 4.  Public Key Subsystem Operations  . . . . . . . . . . . . . . .  7
   4.1.  Adding a Public Key  . . . . . . . . . . . . . . . . . . .  7
   4.2.  Removing a Public Key  . . . . . . . . . . . . . . . . . . 10
   4.3.  Listing Public Keys  . . . . . . . . . . . . . . . . . . . 10
   4.4.  Listing Server Capabilities  . . . . . . . . . . . . . . . 10
 5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11
 6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 12
   6.1.  Registrations  . . . . . . . . . . . . . . . . . . . . . . 12
   6.2.  Names  . . . . . . . . . . . . . . . . . . . . . . . . . . 12
     6.2.1.  Conventions for Names  . . . . . . . . . . . . . . . . 12
     6.2.2.  Future Assignments of Names  . . . . . . . . . . . . . 13
   6.3.  Public Key Subsystem Request Names . . . . . . . . . . . . 13
   6.4.  Public Key Subsystem Response Names  . . . . . . . . . . . 13
   6.5.  Public Key Subsystem Attribute Names . . . . . . . . . . . 13
   6.6.  Public Key Subsystem Status Codes  . . . . . . . . . . . . 14
     6.6.1.  Conventions  . . . . . . . . . . . . . . . . . . . . . 14
     6.6.2.  Initial Assignments  . . . . . . . . . . . . . . . . . 14
     6.6.3.  Future Assignments . . . . . . . . . . . . . . . . . . 15
 7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 15
   7.1.  Normative References . . . . . . . . . . . . . . . . . . . 15
   7.2.  Informative References . . . . . . . . . . . . . . . . . . 15
 8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 16

Galbraith, et al. Standards Track [Page 2] RFC 4819 Secure Shell Public Key Subsystem March 2007

1. Introduction

 Secure Shell (SSH) is a protocol for secure remote login and other
 secure network services over an insecure network.  Secure Shell
 defines a user authentication mechanism that is based on public keys,
 but does not define any mechanism for key distribution.  Common
 practice is to authenticate once with password authentication and
 transfer the public key to the server.  However, to date no two
 implementations use the same mechanism to configure a public key for
 use.
 This document describes a subsystem that can be used to configure
 public keys in an implementation-independent fashion.  This approach
 allows client software to take on the burden of this configuration.
 The Public Key Subsystem protocol is designed for extreme simplicity
 in implementation.  It is not intended as a Public Key Infrastructure
 for X.509 Certificates (PKIX) replacement.
 The Secure Shell Public Key Subsystem has been designed to run on top
 of the Secure Shell transport layer [2] and user authentication
 protocols [3].  It provides a simple mechanism for the client to
 manage public keys on the server.
 This document should be read only after reading the Secure Shell
 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
 fashion before it can be used.  If password authentication is used,
 servers SHOULD provide a configuration option to disable the use of
 password authentication after the first public key is added.

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 RFC 2119 [5].

3. Public Key Subsystem Overview

 The Public Key Subsystem provides a server-independent mechanism for
 clients to add public keys, remove public keys, and list the current
 public keys known by the server.  The subsystem name is "publickey".

Galbraith, et al. Standards Track [Page 3] RFC 4819 Secure Shell Public Key Subsystem March 2007

 The public keys added, removed, and listed using this protocol are
 specific and limited to those of the authenticated user.
 The operations to add, remove, and list the authenticated user's
 public keys are performed as request packets sent to the server.  The
 server sends response packets that indicate success or failure as
 well as provide specific response data.
 The format of public key blobs are detailed in Section 6.6, "Public
 Key Algorithms" of the SSH Transport Protocol document [2].

3.1. Opening the Public Key Subsystem

 The Public Key Subsystem is started by a client sending an
 SSH_MSG_CHANNEL_REQUEST over an existing session's channel.
 The details of how a session is opened are described in the SSH
 Connection Protocol document [4] in the section "Opening a Session".
 To open the Public Key Subsystem, the client sends:
      byte      SSH_MSG_CHANNEL_REQUEST
      uint32    recipient channel
      string    "subsystem"
      boolean   want reply
      string    "publickey"
 Client implementations SHOULD reject this request; it is normally
 sent only by the client.
 If want reply is TRUE, the server MUST respond with
 SSH_MSG_CHANNEL_SUCCESS if the Public Key Subsystem was successfully
 started, or SSH_MSG_CHANNEL_FAILURE if the server failed to start or
 does not support the Public Key Subsystem.
 The server SHOULD respond with SSH_MSG_CHANNEL_FAILURE if the user is
 not allowed access to the Public Key Subsystem (for example, because
 the user authenticated with a restricted public key).
 It is RECOMMENDED that clients request and check the reply for this
 request.

Galbraith, et al. Standards Track [Page 4] RFC 4819 Secure Shell Public Key Subsystem March 2007

3.2. Requests and Responses

 All Public Key Subsystem requests and responses are sent in the
 following form:
      uint32    length
      string    name
      ... request/response specific data follows
 The length field describes the length of the name field and of the
 request/response-specific data, but does not include the length of
 the length field itself.  The client MUST receive acknowledgement of
 each request prior to sending a new request.
 The version packet, as well as all requests and responses described
 in Section 4, are a description of the 'name' field and the data part
 of the packet.

3.3. The Status Message

 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 has been sent.
      string    "status"
      uint32    status code
      string    description [7]
      string    language tag [6]
 A status message MUST be sent for any unrecognized packets, and the
 request SHOULD NOT close the subsystem.

3.3.1. Status Codes

 The status code gives the status in a more machine-readable format
 (suitable for localization), and can have the following values:
      SSH_PUBLICKEY_SUCCESS                      0
      SSH_PUBLICKEY_ACCESS_DENIED                1
      SSH_PUBLICKEY_STORAGE_EXCEEDED             2
      SSH_PUBLICKEY_VERSION_NOT_SUPPORTED        3
      SSH_PUBLICKEY_KEY_NOT_FOUND                4
      SSH_PUBLICKEY_KEY_NOT_SUPPORTED            5
      SSH_PUBLICKEY_KEY_ALREADY_PRESENT          6
      SSH_PUBLICKEY_GENERAL_FAILURE              7
      SSH_PUBLICKEY_REQUEST_NOT_SUPPORTED        8
      SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED      9

Galbraith, et al. Standards Track [Page 5] RFC 4819 Secure Shell Public Key Subsystem March 2007

 If a request completed successfully, the server MUST send the status
 code SSH_PUBLICKEY_SUCCESS.  The meaning of the failure codes is as
 implied by their names.

3.4. The Version Packet

 Both sides MUST start a connection by sending a version packet that
 indicates the version of the protocol they are using.
      string "version"
      uint32 protocol-version-number
 This document describes version 2 of the protocol.  Version 1 was
 used by an early draft of this document.  The version number was
 incremented after changes in the handling of status packets.
 Both sides send the highest version that they implement.  The lower
 of the version numbers is the version of the protocol to use.  If
 either side can't support the lower version, it should close the
 subsystem and notify the other side by sending an
 SSH_MSG_CHANNEL_CLOSE message.  Before closing the subsystem, a
 status message with the status SSH_PUBLICKEY_VERSION_NOT_SUPPORTED
 SHOULD be sent.  Note that, normally, status messages are only sent
 by the server (in response to requests from the client).  This is the
 only occasion on which the client sends a status message.
 Both sides MUST wait to receive this version before continuing.  The
 "version" packet MUST NOT be sent again after this initial exchange.
 The SSH_PUBLICKEY_VERSION_NOT_SUPPORTED status code must not be sent
 in response to any other request.
 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

Galbraith, et al. Standards Track [Page 6] RFC 4819 Secure Shell Public Key Subsystem March 2007

4. Public Key Subsystem Operations

 The Public Key Subsystem currently defines four operations: add,
 remove, list, and listattributes.

4.1. Adding a Public Key

 If the client wishes to add a public key, the client sends:
      string    "add"
      string    public key algorithm name
      string    public key blob
      boolean   overwrite
      uint32    attribute-count
       string    attrib-name
       string    attrib-value
       bool      critical
      repeated attribute-count times
 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
 public key authentications.  If the overwrite field is false and the
 specified key already exists, the server MUST return
 SSH_PUBLICKEY_KEY_ALREADY_PRESENT.  If the server returns this, the
 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
 cannot be overwritten, the server MUST return
 SSH_PUBLICKEY_ACCESS_DENIED.
 Attribute names are defined following the same scheme laid out for
 algorithm names in [1].  If the server does not implement a critical
 attribute, it MUST fail the add, with the status code
 SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED.  For the purposes of a
 critical attribute, mere storage of the attribute is not sufficient
 -- rather, the server must understand and implement the intent of the
 attribute.
 The following attributes are currently defined:
 "comment"
 The value of the comment attribute contains user-specified text about
 the public key.  The server SHOULD make every effort to preserve this
 value and return it with the key during any subsequent list
 operation.  The server MUST NOT attempt to interpret or act upon the
 content of the comment field in any way.  The comment attribute must
 be specified in UTF-8 format [7].

Galbraith, et al. Standards Track [Page 7] RFC 4819 Secure Shell Public Key Subsystem March 2007

 The comment field is useful so the user can identify the key without
 resorting to comparing its fingerprint.  This attribute SHOULD NOT be
 critical.
 "comment-language"
 If this attribute is specified, it MUST immediately follow a
 "comment" attribute and specify the language for that attribute [6].
 The client MAY specify more than one comment if it additionally
 specifies a different language for each of those comments.  The
 server SHOULD attempt to store each comment with its language
 attribute.  This attribute SHOULD NOT be critical.
 "command-override"
 "command-override" specifies a command to be executed when this key
 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
 the command or shell which would otherwise have been executed as a
 result of that request.  If the command string is empty, both "exec"
 and "shell" requests should be denied.  If no "command-override"
 attribute is specified, all "exec" and "shell" requests should be
 permitted (as long as they satisfy other security or authorization
 checks the server may perform).  This attribute SHOULD be critical.
 "subsystem"
 "subsystem" specifies a comma-separated list of subsystems that may
 be started (using a "subsystem" request) when this key is in use.
 This attribute SHOULD be critical.  If the value is empty, no
 subsystems may be started.  If the "subsystem" attribute is not
 specified, no restrictions are placed on which subsystems may be
 started when authenticated using this key.
 "x11"
 "x11" specifies that X11 forwarding may not be performed when this
 key is in use.  The attribute-value field SHOULD be empty for this
 attribute.  This attribute SHOULD be critical.
 "shell"
 "shell" specifies that session channel "shell" requests should be
 denied when this key is in use.  The attribute-value field SHOULD be
 empty for this attribute.  This attribute SHOULD be critical.

Galbraith, et al. Standards Track [Page 8] RFC 4819 Secure Shell Public Key Subsystem March 2007

 "exec"
 "exec" specifies that session channel "exec" requests should be
 denied when this key is in use.  The attribute-value field SHOULD be
 empty for this attribute.  This attribute SHOULD be critical.
 "agent"
 "agent" specifies that session channel "auth-agent-req" requests
 should be denied when this key is in use.  The attribute-value field
 SHOULD be empty for this attribute.  This attribute SHOULD be
 critical.
 "env"
 "env" specifies that session channel "env" requests should be denied
 when this key is in use.  The attribute-value field SHOULD be empty
 for this attribute.  This attribute SHOULD be critical.
 "from"
 "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
 authorization purposes, the authorization attempt MUST be denied.
 The server SHOULD make a log entry regarding this.  The server MAY
 provide a method for administrators to disallow the appearance of a
 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.  For IP-based networks, it is anticipated that each element
 of the "from" parameter will take the form of a specific IP address
 or hostname.
 "port-forward"
 "port-forward" specifies that no "direct-tcpip" requests should be
 accepted, except those to hosts specified in the comma-separated list
 supplied as a value to this attribute.  If the value of this
 attribute is empty, all "direct-tcpip" requests should be refused
 when using this key.  This attribute SHOULD be critical.
 "reverse-forward"
 "reverse-forward" specifies that no "tcpip-forward" requests should
 be accepted, except for the port numbers in the comma-separated list
 supplied as a value to this attribute.  If the value of this
 attribute is empty, all "tcpip-forward" requests should be refused
 when using this key.  This attribute SHOULD be critical.

Galbraith, et al. Standards Track [Page 9] RFC 4819 Secure Shell Public Key Subsystem March 2007

 In addition to the attributes specified by the client, the server MAY
 provide a method for administrators to enforce certain attributes
 compulsorily.

4.2. Removing a Public Key

 If the client wishes to remove a public key, the client sends:
      string    "remove"
      string    public key algorithm name
      string    public key blob
 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
 subsequent authentications.

4.3. Listing Public Keys

 If the client wishes to list the known public keys, the client sends:
      string    "list"
 The server will respond with zero or more of the following responses:
      string    "publickey"
      string    public key algorithm name
      string    public key blob
      uint32    attribute-count
       string    attrib-name
       string    attrib-value
      repeated attribute-count times
 There is no requirement that the responses be in any particular
 order.  Whilst some server implementations may send the responses in
 some order, client implementations should not rely on responses being
 in any order.
 Following the last "publickey" response, a status packet MUST be
 sent.
 Implementations SHOULD support this request.

4.4. Listing Server Capabilities

 If the client wishes to know which key attributes the server
 supports, it sends:
      string    "listattributes"

Galbraith, et al. Standards Track [Page 10] RFC 4819 Secure Shell Public Key Subsystem March 2007

 The server will respond with zero or more of the following responses:
      string    "attribute"
      string    attribute name
      boolean   compulsory
 The "compulsory" field indicates whether this attribute will be
 compulsorily applied to any added keys (irrespective of whether the
 attribute has been specified by the client) due to administrative
 settings on the server.  If the server does not support
 administrative settings of this nature, it MUST return false in the
 compulsory field.  An example of use of the "compulsory" attribute
 would be a server with a configuration file specifying that the user
 is not permitted shell access.  Given this, the server would return
 the "shell" attribute, with "compulsory" marked true.  Whatever
 attributes the user subsequently asked the server to apply to their
 key, the server would also apply the "shell" attribute, rendering it
 impossible for the user to use a shell.
 Following the last "attribute" response, a status packet MUST be
 sent.
 An implementation MAY choose not to support this request.

5. Security Considerations

 This protocol assumes that it is run over a secure channel and that
 the endpoints of the channel have been authenticated.  Thus, this
 protocol assumes that it is externally protected from network-level
 attacks.
 This protocol provides a mechanism that allows client authentication
 data to be uploaded and manipulated.  It is the responsibility of the
 server implementation to enforce any access controls that may be
 required to limit the access allowed for any particular user (the
 user being authenticated externally to this protocol, typically using
 the SSH User Authentication Protocol [3]).  In particular, it is
 possible for users to overwrite an existing key on the server with
 this protocol, whilst at the same time specifying fewer restrictions
 for the new key than were previously present.  Servers should take
 care that when doing this, clients are not able to override presets
 from the server's administrator.
 This protocol requires the client to assume that the server will
 correctly implement and observe attributes applied to keys.
 Implementation errors in the server could cause clients to authorize
 keys for access they were not intended to have, or to apply fewer
 restrictions than were intended.

Galbraith, et al. Standards Track [Page 11] RFC 4819 Secure Shell Public Key Subsystem March 2007

6. IANA Considerations

 This section contains conventions used in naming the namespaces, the
 initial state of the registry, and instructions for future
 assignments.

6.1. Registrations

 Consistent with Section 4.9.5 of [8], this document makes the
 following registration:
 The subsystem name "publickey".

6.2. Names

 In the following sections, the values for the namespaces 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.

6.2.1. 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 (","), or whitespace or control characters
 (ASCII codes 32 or less).  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 (","), or
 whitespace, or control characters (ASCII codes 32 or less).  The part
 following the at-sign MUST be a valid, fully qualified Internet
 domain name [10] 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 [9]
 email addresses.  This is purely coincidental and actually has
 nothing to do with STD 11 [9].  An example of a locally defined name
 is "our-attribute@example.com" (without the double quotes).

Galbraith, et al. Standards Track [Page 12] RFC 4819 Secure Shell Public Key Subsystem March 2007

6.2.2. Future Assignments of Names

 Requests for assignments of new Names MUST be done through the IETF
 Consensus method as described in [11].

6.3. Public Key Subsystem Request Names

 The following table lists the initial assignments of Public Key
 Subsystem Request names.
         Request Name
         -------------
         version
         add
         remove
         list
         listattributes

6.4. Public Key Subsystem Response Names

 The following table lists the initial assignments of Public Key
 Subsystem Response names.
         Response Name
         --------------
         version
         status
         publickey
         attribute

6.5. Public Key Subsystem Attribute Names

 Attributes are used to define properties or restrictions for public
 keys.  The following table lists the initial assignments of Public
 Key Subsystem Attribute names.

Galbraith, et al. Standards Track [Page 13] RFC 4819 Secure Shell Public Key Subsystem March 2007

         Attribute Name
         ---------------
         comment
         comment-language
         command-override
         subsystem
         x11
         shell
         exec
         agent
         env
         from
         port-forward
         reverse-forward

6.6. Public Key Subsystem Status Codes

 The status code is a byte value, describing the status of a request.

6.6.1. Conventions

 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
 reserved for use by local, private extensions.

6.6.2. Initial Assignments

 The following table identifies the initial assignments of the Public
 Key Subsystem status code values.
         Status code                           Value    Reference
         ------------                          -----    ---------
         SSH_PUBLICKEY_SUCCESS                   0
         SSH_PUBLICKEY_ACCESS_DENIED             1
         SSH_PUBLICKEY_STORAGE_EXCEEDED          2
         SSH_PUBLICKEY_VERSION_NOT_SUPPORTED     3
         SSH_PUBLICKEY_KEY_NOT_FOUND             4
         SSH_PUBLICKEY_KEY_NOT_SUPPORTED         5
         SSH_PUBLICKEY_KEY_ALREADY_PRESENT       6
         SSH_PUBLICKEY_GENERAL_FAILURE           7
         SSH_PUBLICKEY_REQUEST_NOT_SUPPORTED     8
         SSH_PUBLICKEY_ATTRIBUTE_NOT_SUPPORTED   9

Galbraith, et al. Standards Track [Page 14] RFC 4819 Secure Shell Public Key Subsystem March 2007

6.6.3. Future Assignments

 Requests for assignments of new status codes in the range of 0 to 191
 MUST be done through the Standards Action method as described in
 [11].
 The IANA will not control the status code range of 192 through 255.
 This range is for private use.

7. References

7.1. Normative References

 [1]   Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Protocol
       Architecture", RFC 4251, January 2006.
 [2]   Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Transport
       Layer Protocol", RFC 4253, January 2006.
 [3]   Ylonen, T. and C. Lonvick, "The Secure Shell (SSH)
       Authentication Protocol", RFC 4252, January 2006.
 [4]   Ylonen, T. and C. Lonvick, "The Secure Shell (SSH) Connection
       Protocol", RFC 4254, January 2006.
 [5]   Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997.
 [6]   Phillips, A. and M. Davis, "Tags for Identifying Languages",
       BCP 47, RFC 4646, September 2006.
 [7]   Yergeau, F., "UTF-8, a transformation format of ISO 10646",
       STD 63, RFC 3629, November 2003.

7.2. Informative References

 [8]   Lehtinen, S. and C. Lonvick, "The Secure Shell (SSH) Protocol
       Assigned Numbers", RFC 4250, January 2006.
 [9]   Crocker, D., "Standard for the format of ARPA Internet text
       messages", STD 11, RFC 822, August 1982.
 [10]  Mockapetris, P., "Domain names - concepts and facilities",
       STD 13, RFC 1034, November 1987.
 [11]  Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
       Considerations Section in RFCs", BCP 26, RFC 2434,
       October 1998.

Galbraith, et al. Standards Track [Page 15] RFC 4819 Secure Shell Public Key Subsystem March 2007

8. Acknowledgements

 Brent McClure contributed to the writing of this document.

Authors' Addresses

 Joseph Galbraith
 VanDyke Software
 4848 Tramway Ridge Blvd
 Suite 101
 Albuquerque, NM  87111
 US
 Phone: +1 505 332 5700
 EMail: galb@vandyke.com
 Jeff P. Van Dyke
 VanDyke Software
 4848 Tramway Ridge Blvd
 Suite 101
 Albuquerque, NM  87111
 US
 Phone: +1 505 332 5700
 EMail: jpv@vandyke.com
 Jon Bright
 Silicon Circus
 24 Jubilee Road
 Chichester, West Sussex  PO19 7XB
 UK
 Phone: +49 172 524 0521
 EMail: jon@siliconcircus.com

Galbraith, et al. Standards Track [Page 16] RFC 4819 Secure Shell Public Key Subsystem March 2007

Full Copyright Statement

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 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.
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 "AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS
 OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
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 OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
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 WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

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 specification can be obtained from the IETF on-line IPR repository at
 http://www.ietf.org/ipr.
 The IETF invites any interested party to bring to its attention any
 copyrights, patents or patent applications, or other proprietary
 rights that may cover technology that may be required to implement
 this standard.  Please address the information to the IETF at
 ietf-ipr@ietf.org.

Acknowledgement

 Funding for the RFC Editor function is currently provided by the
 Internet Society.

Galbraith, et al. Standards Track [Page 17]

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