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Network Working Group                                       J. GalbraithRequest for Comments: 4819                                   J. Van DykeCategory: Standards Track                               VanDyke Software                                                               J. Bright                                                          Silicon Circus                                                              March 2007Secure Shell Public Key SubsystemStatus 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 2007Table of Contents1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .32.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .33.  Public Key Subsystem Overview  . . . . . . . . . . . . . . . .33.1.  Opening the Public Key Subsystem . . . . . . . . . . . . .43.2.  Requests and Responses . . . . . . . . . . . . . . . . . .53.3.  The Status Message . . . . . . . . . . . . . . . . . . . .53.3.1.  Status Codes . . . . . . . . . . . . . . . . . . . . .53.4.  The Version Packet . . . . . . . . . . . . . . . . . . . .64.  Public Key Subsystem Operations  . . . . . . . . . . . . . . .74.1.  Adding a Public Key  . . . . . . . . . . . . . . . . . . .74.2.  Removing a Public Key  . . . . . . . . . . . . . . . . . .104.3.  Listing Public Keys  . . . . . . . . . . . . . . . . . . .104.4.  Listing Server Capabilities  . . . . . . . . . . . . . . .105.  Security Considerations  . . . . . . . . . . . . . . . . . . .116.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .126.1.  Registrations  . . . . . . . . . . . . . . . . . . . . . .126.2.  Names  . . . . . . . . . . . . . . . . . . . . . . . . . .126.2.1.  Conventions for Names  . . . . . . . . . . . . . . . .126.2.2.  Future Assignments of Names  . . . . . . . . . . . . .136.3.  Public Key Subsystem Request Names . . . . . . . . . . . .136.4.  Public Key Subsystem Response Names  . . . . . . . . . . .136.5.  Public Key Subsystem Attribute Names . . . . . . . . . . .136.6.  Public Key Subsystem Status Codes  . . . . . . . . . . . .146.6.1.  Conventions  . . . . . . . . . . . . . . . . . . . . .146.6.2.  Initial Assignments  . . . . . . . . . . . . . . . . .146.6.3.  Future Assignments . . . . . . . . . . . . . . . . . .157.  References . . . . . . . . . . . . . . . . . . . . . . . . . .157.1.  Normative References . . . . . . . . . . . . . . . . . . .157.2.  Informative References . . . . . . . . . . . . . . . . . .158.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .16Galbraith, et al.           Standards Track                     [Page 2]

RFC 4819           Secure Shell Public Key Subsystem          March 20071.  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 inRFC 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 inSection 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 20073.2.  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   inSection 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      9Galbraith, 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   0x6EGalbraith, et al.           Standards Track                     [Page 6]

RFC 4819           Secure Shell Public Key Subsystem          March 20074.  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 20076.  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 20076.2.2.  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           listattributes6.4.  Public Key Subsystem Response Names   The following table lists the initial assignments of Public Key   Subsystem Response names.           Response Name           --------------           version           status           publickey           attribute6.5.  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-forward6.6.  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   9Galbraith, et al.           Standards Track                    [Page 14]

RFC 4819           Secure Shell Public Key Subsystem          March 20076.6.3.  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.  References7.1.  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 20078.  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.comGalbraith, et al.           Standards Track                    [Page 16]

RFC 4819           Secure Shell Public Key Subsystem          March 2007Full Copyright Statement   Copyright (C) The IETF Trust (2007).   This document is subject to the rights, licenses and restrictions   contained inBCP 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, THE IETF TRUST 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   WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Intellectual Property   The IETF takes no position regarding the validity or scope of any   Intellectual Property Rights or other rights that might be claimed to   pertain to the implementation or use of the technology described in   this document or the extent to which any license under such rights   might or might not be available; nor does it represent that it has   made any independent effort to identify any such rights.  Information   on the procedures with respect to rights in RFC documents can be   found inBCP 78 andBCP 79.   Copies of IPR disclosures made to the IETF Secretariat and any   assurances of licenses to be made available, or the result of an   attempt made to obtain a general license or permission for the use of   such proprietary rights by implementers or users of this   specification can be obtained from the IETF on-line IPR repository athttp://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]