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Versions: 00 01 02 03 04 05 06 07 08                                    
Kerberos Working Group                                  Nicolas Williams
INTERNET-DRAFT                                          Sun Microsystems
Category: Standards Track                               Jonathan Trostle
                                                           Cisco Systems
                                                              Mike Swift
                                                        University of WA
                                                             John Brezak
                                                               Microsoft
                                                            Bill Gossman
                                                           Cisco Systems



                Kerberos Set/Change Password: Version 2
              <draft-ietf-krb-wg-kerberos-set-passwd-01.txt>




Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [RFC2026].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups.  Note that
   other groups may also distribute working documents as Internet-
   Drafts.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet- Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   http://www.ietf.org/ietf/1id-abstracts.txt

   The list of Internet-Draft Shadow Directories can be accessed at
   http://www.ietf.org/shadow.html.

   This draft expires on December 31st, 2001. Please send comments to
   the authors.


Copyright Notice

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

Abstract

   This document specifies an extensible protocol for setting keys and
   changing the passwords of Kerberos V principals.



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Table of Contents

   1  Introduction
   2  The Protocol
   2.1  Transports
   2.2  Protocol Framing
   2.2.1  The protocol over UDP
   2.2.2  The protocol over TCP
   2.3  Protocol version negotiation
   2.3.1  Protocol major version negotiation
   2.3.2  Protocol minor version negotiation
   2.4  Use of Kerberos V
   2.5  Use of ASN.1
   2.6  Internationalization
   2.6.1  Normalization Forms for UTF-8 Strings
   2.6.2  Language Negotiation
   2.7  Protocol Extensibility
   2.8  Protocol Subsets
   3  Protocol Elements
   3.1  PDUs
   3.2  Operations
   3.2.1  Null
   3.2.2  Change Kerberos Password
   3.2.3  Set Kerberos Password
   3.2.4  Set Kerberos Keys
   3.2.5  Generate Kerberos Keys
   3.2.6  Get New Keys
   3.2.7  Commit New Keys
   3.2.8  Get Password Quality Policy
   3.2.9  Get Principal Aliases
   3.2.10  Get Realm's Supported Kerberos V Version and Features
   4  ASN.1 Module
   6  IANA Considerations
   7  Security Considerations
   8  Acknowledgements
   9  References
   9.1  Normative References
   9.2  Informative References
   10  Authors' Addresses
   11  Notes to the RFC Editor

Conventions used in this document

   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].

1  Introduction

   Up to this point Kerberos V has lacked a single, standard protocol
   for changing passwords and keys.  While several vendor-specific

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   protocols exist for changing Kerberos passwords/keys, none are
   properly internationalized and all are incomplete in one respect or
   another and none are sufficiently extensible to cope with new
   features that may be added to Kerberos V at some future time.

   This document defines a protocol that is somewhat backward-compatible
   with the "kpasswd" protocol, version 1 [KPASSWDv1] and a derivative
   defined in [RFC3244] that uses more or less the same protocol
   framing.

   This new protocol is designed to be extensible and properly
   internationalized.

2  The Protocol

   The structure of the protocol is quite similar to that of typical RPC
   protocols.  Each transaction consists of a data structure specific to
   an operation which is then wrapped in a data structure which is
   general to all operations of the protocol.  These data structures are
   defined with the Abstract Syntax Notation 1 (ASN.1) [X680] and they
   are encoded using the Distinguished Encoding Rules (DER) [X690].

   The protocol data is wrapped in a KRB-PRIV, or, in some cases, a
   KRB-ERROR, and framed in a header that is backwards compatible with
   version 1 [KPASSWDv1] of this protocol and [RFC3244].

   [Discussion:  Should the v1/rfc3244 framing and port numbers be
                 dropped?]

2.1  Transports

   The service SHOULD accept requests on UDP port 464 and TCP port 464.
   This is the same port used by version 1 [KPASSWDv1] of this protocol,
   but version 2 is a completely different protocol sharing with
   [KPASSWDv1] and [RFC3244] only the outer framing.

   [Discussion:  Should we remove UDP support?  I think so [Nico].]

2.2  Protocol Framing

   For compatibility with the original Kerberos password changing
   protocol developed at MIT as well as RFC3244, the first 4 bytes of
   the message consist of a 2-byte network byte order message length,
   followed by a 2 byte network byte order protocol version number,
   followed by a 2 byte network byte order length for an optional
   AP-REQ, AP-REP or KRB-ERROR, followed by the same, if present,
   followed by a KRB-PRIV (optional in TCP) containing the actual
   protocol message encoded in DER [X690].

   In the case of TCP there is an additional 4 byte network byte order
   length prepended to the frame described above as per-RFC3244.

   The protocol version number MUST be set to 2 for this protocol.

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   Bytes on the wire description of the framing:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         message length        |    protocol version number    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | AP-REQ length (0 if absent)   | AP-REQ data (if present)      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   KRB-PRIV message                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The same framing applies equally to requests and responses, but
   responses use AP-REP and/or KRB-ERROR instead of AP-REQ:

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         message length        |    protocol version number    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | AP-REP length (0 if absent)   | AP-REP data (if present)      |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   KRB-PRIV message                            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       0                   1                   2                   3
       0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |         message length        |    protocol version number    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | KRB-ERROR length (0 if absent)| KRB-ERROR data (if present)   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   For the UDP case the AP-REQ/AP-REP/KRB-ERROR MUST always be included.

   Note that this framing is used by version 1 [KPASSWDv1] and version
   0xff80 [RFC3244], though the latter does not use the framing when
   responding with KRB-ERROR messages.

   Version 0xff80 servers may respond to requests with an un-framed
   KRB-ERROR and e-data set as per-RFC3244 [RFC3244], otherwise clients
   and server MUST always use this framing.  See section 2.3.

2.2.1  The protocol over UDP

   In the UDP case there is a single message from the client and a
   single response from the server with no state kept between requests,
   and each request MUST include a Kerberos AP-REQ and a KRB-PRIV and
   each response MUST carry an AP-REP, or KRB-ERROR and a KRB-PRIV.

   Both the client and server MUST destroy the sub-session key, if any,
   resulting from the AP exchange after each operation.

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   UDP clients MUST not request the use of sequence numbers, otherwise
   they cannot generate the KRB-PRIV prior to receiving the AP-REP.

2.2.2  The protocol over TCP

   The initial message from the client MUST carry an AP-REQ and the
   response to any request bearing an AP-REQ MUST carry an AP-REP.

   Subsequent messages MAY involve Kerberos V AP exchanges, but
   generally the client SHOULD NOT initiate a new AP exchange except
   when it desires to authenticate as a different principal, when the
   ticket last used for authentication expires or when the server
   responds with an error indicating that the client must
   re-authenticate.

   KRB-PRIV messages should use the session or sub-session key
   established in the most recent AP exchange performed over the same
   TCP connection.

   After each new AP exchange the client and server MUST destroy the
   sub-session key, if any, resulting from the previous AP exchange.

   Servers MAY close open sessions at any time.

2.3  Protocol version negotiation

   There are several major versions of this protocol.  Version 2 also
   introduces a notion of protocol minor versions for use in negotiating
   protocol extensions.  As of this time only one minor version is
   defined for major version 2: minor version 0, defined herein.

2.3.1  Protocol major version negotiation

   Version 2 clients that also support other versions, such as
   [KPASSWDv1] or [RFC3244] SHOULD attempt to use version 2 of the
   protocol first and then MAY try other versions if the server responds
   with either a message framed as described in section 2.2 but with a
   protocol version number other than 2, or a KRB-ERROR with an error
   code of KRB5_KPASSWD_BAD_VERSION in the e-data field.

   Note that some version 1 servers return a KRB-ERROR indicating that
   versions other than 1 of the change password protocol are not
   supported rather than an AP-REP and a KRB-PRIV containing the error
   data.

   Also note that some [RFC3244] implementations do not return any
   responses to requests for protocol versions other than 0xff80, and in
   the TCP case close the TCP connection.

   As a result change password protocol major version negotiation is
   subject to downgrade attacks.  Therefore major version negotiation is
   NOT RECOMMENDED.

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   Version 2 servers SHOULD respond to non-v2 requests using whatever
   response is appropriate for the versions used by the clients, but if
   a server does not do this or know how to do this then it MUST respond
   with an error framed as in section 2.2, using an AP-REP and KRB-PRIV
   if the client's AP-REQ can be accepted, or a KRB-ERROR (framed)
   otherwise and using a ProtocolErrorCode value of
   unsupported-major-version or .

2.3.2  Protocol minor version negotiation

   Version 2 clients are free to use whatever protocol minor version and
   message extensions are available to them in their initial messages to
   version 2 servers, provided that the minor versions (other than 0)
   have been defined through IETF documents and registered with the
   IANA.

   Version 2 servers MUST answer with the highest protocol minor version
   number supported by the server and the client.

   Version 2 clients MUST use the protocol minor version used in a
   server's reply for any subsequent messages in the same TCP session.

   See section 2.7 for further description of the protocol's
   extensibility and its relation to protocol minor versions and the
   negotiation thereof.

2.4  Use of Kerberos V

   This protocol makes use of messages defined in [RFC1510] and
   [clarifications].  Specifically, AP-REQ, AP-REP, KRB-ERROR and
   KRB-PRIV.

   All operations are to be performed by the server on behalf of the
   client principal.

   Clients SHOULD use "kadmin/setpw" as the principal name of the server
   for all requests except when changing the client principal's own
   password, when expired, for which they should use "kadmin/changepw".

   The client MUST request mutual authentication and the client MUST NOT
   request the use of sequence numbers when using the protocol over
   UDP, but it MUST request the use of sequence numbers when running
   over TCP.

   Clients SHOULD use INITIAL tickets for change password requests.
   Servers MAY force the use of INITIAL tickets for any request - see
   section 3.2.

2.5  Use of ASN.1

   This protocol's messages are defined in ASN.1, using only features
   from [X680].  All ASN.1 types defined herein are to be encoded in

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   DER [X690].  A complete ASN.1 module is given in section 4.  The
   ASN.1 tagging environment for this module is EXPLICIT.

   The DER encoding of the ASN.1 PDUs are exchanged wrapped in a
   KRB-PRIV as described above and/or as e-data in KRB-ERROR messages.

2.6  Internationalization

   This protocol's request PDU carries an optional field indicating the
   languages spoken by the client user; the client SHOULD send its list
   of spoken languages to the server (once per-TCP session).  All
   strings in the protocol are UTF-8 strings.

   The server SHOULD localize all strings intended for users to a
   language in common with the languages spoken by the client user.

   For TCP sessions servers MUST cache the optional language tag lists
   from prior requests for use with subsequent requests that exclude the
   language tag list.  Clients MAY expect such server behaviour and send
   the language tag lists only when they change or even just once
   per-TCP session.  Clients SHOULD send the server the language tag
   list at least once.

   Kerberos principal and realm names used in this protocol MUST be
   constrained as per the specification of the version of Kerberos V
   used by the client.

2.6.1  Normalization Forms for UTF-8 Strings

   No normalization form is required for string types other than
   for PrincipalName and Realm, which two types are constrained by the
   specification of the version of Kerberos V used by the client, and
   the password fields in the change password operation, which MUST be
   normalized according to [k5stringprep].

2.6.2  Language Negotiation

   The server MUST pick a language from the client's input list or
   the default language tag (see [RFC3066]) for text in its responses
   which is meant for the user to read.

   The server SHOULD use a language selection algorithm such that
   consideration is first given to exact matches between the client's
   spoken languages and the server's available locales, followed by
   "fuzzy" matches where only the first sub-tags of the client's
   language tag list are used for matching against the servers available
   locales.

   When the server has a message catalog for one of the client's spoken
   languages the server SHOULD localize any text strings intended for
   users to read.

2.7  Protocol Extensibility

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   The protocol is defined in ASN.1 and uses extensibility markers
   throughout.  As such, the module presented herein can be extended
   within the framework of [X680].

   Typed holes are not used in this protocol as it is very simple and
   does not require the ability to deal with abstract data types defined
   in different layers.  For this reason, the only way to extend this
   protocol is by extending the ASN.1 module within the framework of the
   IETF; all future extensions to this protocol have to be defined in
   IETF documents unless otherwise specified in a future IETF revision
   of this protocol.

   A protocol minor version number is used to negotiate use of
   extensions.  See section 2.3.2 for the minor version negotiation.

   Message extensions are to be closely tied to protocol minor numbers.

   Clients MAY use any protocol minor version that they support in
   initial requests, and MUST use the protocol minor version indicated
   in the server's initial reply in any subsequent requests in the same
   TCP session.

   Servers SHOULD ignore additions to the ASN.1 types, in initial
   requests, where the syntax allows them that they do not understand,
   except for extensions to the "Op-req" type, which MUST result in an
   error; servers MAY respond with an error (ProtocolErrorCode value of
   unsupported-minor-version) to clients that use minor versions
   unsupported by the server in their initial requests.

   Servers MUST select the highest minor version in common with their
   clients for use in replies.

2.8  Protocol Subsets

   The structure of the protocol is such that the ASN.1 syntaxes for the
   various operations supported by the protocol are independent of the
   each other.  Client and server mplementations MAY implement subsets
   of the overall protocol by removing some alternatives to the Op-req,
   Op-rep and Op-err CHOICEs from the ASN.1 module given in section 4.

   For example, it should be possible to have a password-change only
   client that cannot set principal's keys - and vice versa.

3  Protocol Elements

   The protocol as defined herein supports the following operations
   relating to the management of Kerberos principal's passwords or keys:

     - change password
     - set password (administrative)
     - set new keys
     - generate new keys

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     - get new, un-committed keys
     - commit new keys
     - get password policy name and/or description of principal
     - list aliases of a principal
     - list enctypes and version of Kerberos V supported by realm

   These operations are needed to support Kerberos V interoperability
   between clients and KDCs of different implementation origins.

   The operation for retrieving a list of aliases of a principal is
   needed where KDCs implement aliasing of principal names and allows
   clients to properly setup their "keytabs" when principal aliasing is
   in use.

   Operations such as creation or deletion of principals are outside the
   scope of this document, and should be performed via other means, such
   as through directories or other Kerberos administration protocols.

   The individual operations are described in section 3.2.

3.1  PDUs

   The types "Request," "Response" and "Error-Response" are the ASN.1
   module's PDUs.

   The "Request" and "Response" PDUs are always to be sent wrapped in
   KRB-PRIV messages, except for the "Error-Response" PDU which MUST be
   sent as KRB-ERROR e-data (see section 2.4.1) when AP exchanges fail,
   otherwise it MUST be sent wrapped in a KRB-PRIV.

   The ASN.1 syntax for the PDUs is given in section 4.

   Note that the first field of each PDU is the major version of the
   protocol, defaulted to 2, meaning that it is never included in
   version 2 exchanges.  Similarly, the second field of each PDU is the
   minor version, defaulted to 0.

   The request, responses and error PDUs consist of an outer structure
   ("Request," "Response" and "Error-Response") containing fields common
   to all requests/responses, and an inner structure for fields that are
   specific to each operation's requests/responses.  The inner structure
   is optional in the case of the Error-Response PDU and need not be
   included when generic errors occur for which there is a suitable
   ProtocolErrorCode.

   Specifically, the outer Request structure has a field for passing a
   client user's spoken (read) languages to the server.  It also has two
   optional fields for identifying the requested operation's target
   principal's name and realm (if not sent then the server MUST use the
   client principal name and realm from the AP exchange as the target).

   The Response and Error PDUs' outer structures include a field
   indicating the language that the server has chosen for localization

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   of text intended to be displayed to users; this field is defaulted
   to "i-default".  This language tag applies to all UTF8 strings
   in the inner structure (Op-rep and Op-err) that are meant to be
   displayed to users.

   The protocol error codes are:

      - proto-generic-error

        An operation-specific error ocurred, see the inner Op-error.

      - proto-format-error
      - proto-unsupported-major-version
      - proto-unsupported-minor-version
      - proto-unsupported-operation

      - proto-wrong-service-principal

        Use kadmin/setpw for the server's principal name.

      - proto-re-authentication-required

        The server demands that the client re-authenticate through a new
        AP exchange.

      - proto-initial-ticket-required

        Use of an INITIAL ticket is required for the requested
        operation.

      - proto-client-and-target-realm-mismatch

        The server requires that the client's principal name and the
        target principal of the operation share the same realm name.

      - proto-target-principal-unknown
      - proto-authorization-failed

3.2  Operations

   This section describes the semantics of each operation request and
   response defined in the ASN.1 module in section 4.

3.2.1  Null

   NAME

      null - Null or "ping" operation

   DESCRIPTION

      The null request is intended for use with TCP; its purpose is
      similar to RPC null procedures and is akin to a "ping" operation.

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   ERRORS

      None.

3.2.2  Change Kerberos Password

   NAME

      change-pw - Change password operation

   SYNOPSIS

      Req-change-pw(old-pw, [new-pw], [etypes]) ->
         Rep-change-pw([info-text], [new-pw], [etypes]) |
         Err-change-pw([help-text], error code, [error info])

   DESCRIPTION

      Change a principal's password.

      The change password request has one required field and three
      optional fields: "old-pw" (required), "new-pw" and "etypes",
      corresponding to the target principal's old password, new password
      and desired enctypes for the new long-term keys.

      The server MUST validate the old password and MUST check the
      quality of the new password, if sent, according the password
      quality policy associated with the target principal.

      The server SHOULD require that the old password be sent or that
      the client's ticket be INITIAL, or both, when the client principal
      and the target principal are the same.

      A client MAY request that the server generate a new password by
      excluding the new password from its request, in which case the
      server MUST either generate a new password or respond with an
      error indicating that it does not support this feature.

      Server-generated passwords MUST meet the target principal's
      password quality policy.  It is RECOMMENDED that server-generated
      passwords be user-friendly, that is, memorable and that the target
      principal's preferred languages be taken into account by the
      password generation alogrithm used by the server.

   RETURN

      Upon successful password changes the server responds with a
      Rep-change-pw.  The fields of Rep-change-pw are all optional and
      include:

         - 'info-text' which the server can use to send a message to the
           user such as "Your new password will expire in 90 days," for

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           example.

         - 'new-pw' which the server MUST include if the client
           requested that the server generate a new password; generated
           passwords MUST pass the target principal's password quality
           policy.

         - 'etypes' which the server MAY include to indicate which types
           of long-term keys it created for the target principal and
           which the server MUST include if the client specified a set
           of enctypes in its request.

   ERRORS

      The server may respond to change password requests with protocol
      or operation errors.  See section 3.1 for a description of
      protocol error codes.

      All operation errors include an optional 'help-text' field by
      which the server can describe the error in a human-readable,
      localizaed string.

      Change password error codes include:

         - generic-error

         - old-pw-incorrect

         - wont-generate-new-pw

           The server will not generate a new password for this
           principal or does not support password generation in general.

         - new-pw-rejected-generic

           The client's proposed new password failed the target
           principal's password quality policy.

           The server MUST include a description of the password quality
           policy or aspect of it that the client's proposed new
           password failed to meet.

           The server MAY generate and send a new password that the
           client can then use as a new password and which is guaranteed
           to pass the target principal's current password quality
           policy.

         - etype-not-supported

           The client requested an enctype that the KDC does not
           support.

3.2.3  Set Kerberos Password

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   NAME

      set-pw - Set password operation

   SYNOPSIS

      Req-set-pw([languages], [new-pw], [etypes]) ->
         Rep-set-pw([info-text], [new-pw], [etypes]) |
         Err-set-pw([help-text], error code, [error info])

   DESCRIPTION

      Administratively set a principal's password.

      The change password request has three optional fields:
      "languages", "new-pw" and "etypes", corresponding to the target
      principal's preferred languages, new password and desired enctypes
      for the new long-term keys.

      The server MUST check the quality of the new password, if sent,
      according the password quality policy associated with the target
      principal.

      The server SHOULD require that the client use the change-pw
      operation instead of set-pw when the client principal and the
      target principal are the same.

      A client MAY request that the server generate a new password by
      excluding the new password from its request, in which case the
      server MUST either generate a new password or respond with an
      error indicating that it does not support this feature.

      Server-generated passwords MUST meet the target principal's
      password quality policy.  It is RECOMMENDED that server-generated
      passwords be user-friendly, that is, memorable and that the target
      principal's preferred languages be taken into account by the
      password generation alogrithm used by the server.

   RETURN

      Upon successful password changes the server responds with a
      Rep-change-pw.  The fields of Rep-change-pw are all optional and
      include:

         - 'info-text' which the server can use to send a message to the
           user such as "Your new password will expire in 90 days," for
           example.

         - 'new-pw' which the server MUST include if the client
           requested that the server generate a new password; generated
           passwords MUST pass the target principal's password quality
           policy.

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         - 'etypes' which the server MAY include to indicate which types
           of long-term keys it created for the target principal and
           which the server MUST include if the client specified a set
           of enctypes in its request.

   ERRORS

      The server may respond to change password requests with protocol
      or operation errors.  See section XYZ for a description of
      protocol error codes.

      All operation errors include an optional 'help-text' field by
      which the server can describe the error in a human-readable,
      localizaed string.

      Change password error codes include:

         - generic-error

         - use-change-pw

           The server demands that the client use the change-pw
           operation for the target principal of the set-pw request.

         - wont-generate-new-pw

           The server will not generate a new password for this
           principal or does not support password generation in general.

         - new-pw-rejected-generic

           The client's proposed new password failed the target
           principal's password quality policy.

           The server MUST include a description of the password quality
           policy or aspect of it that the client's proposed new
           password failed to meet.

           The server MAY generate and send a new password that the
           client can then use as a new password and which is guaranteed
           to pass the target principal's current password quality
           policy.

         - etype-not-supported

           The client requested an enctype that the KDC does not
           support.

3.2.4  Set Kerberos Keys

   NAME


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      set-keys

   SYNOPSIS

      Req-set-keys(new-keys, commit?, [isupport]) ->
         Rep-set-keys([info-text], kvno, aliases, [isupport])

   DESCRIPTION

      The set-keys request consists of two required fields and one
      optional field: "new-keys", "commit" (a boolean field - see below)
      and "isupport", an optional field for indicating to the KDC what
      Kerberos V features are supported by the target principal.

      When "commit" is true the KDC makes the new keys available for
      issueing tickets encrypted in them immediately.  Otherwise the
      client MUST follow up with a commit-keys request to make the keys
      available.

      If a principal has keys are awaiting commitment when a new
      set-keys request for that principal s made then the KDC MUST
      overwrite the deferred keys.

   RETURN

      For successful set-keys operations the server returns:

         - Informational text, optional.

         - The new kvno for the target principal.

         - A list of aliases of the target principal known to the KDC
           (optional).

         - The set of Kerberos V features supported by the KDC
           (optional).

   ERRORS

      The server may respond with the following errors:

         - generic
         - deferred-commit-no-support
         - etype-no-support

3.2.5  Generate Kerberos Keys

   NAME

      gen-keys

   SYNOPSIS


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      Req-gen-keys(etypes, [entropy], commit?, [isupport]) ->
         Rep-set-keys([info-text], key, kvno, aliases, [isupport])

   DESCRIPTION

      The gen-keys is similar to the set-keys request (see section
      3.2.4) but differs in that the server generates keys of
      client-requested enctypes, rather than the client providing
      specific keys.

      The gen-keys request consists of two required fields and two
      optional fields: "etypes" (the enctypes of the new keys),
      "entropy", "commit" and "isupport" (see section 3.2.4).

      If a principal has keys are awaiting commitment when a new
      set-keys request for that principal s made then the KDC MUST
      overwrite the deferred keys.

   RETURN

      For successful set-keys operations the server returns:

         - Informational text, optional.

         - The new kvno for the target principal.

         - The new key (only one is needed).

         - A list of aliases of the target principal known to the KDC
           (optional).

         - The set of Kerberos V features supported by the KDC
           (optional).

   ERRORS

      The server may respond with the following errors:

         - generic
         - deferred-commit-no-support
         - etype-no-support

3.2.6  Get New Keys

   NAME

      get-keys

   SYNOPSIS

      Req-get-keys(kvno) ->
         Rep-get-keys([info-text], keys, aliases, [isupport]) |
         Err-get-keys([help-text], error code, [error info])

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   DESCRIPTION

      This request allows a client to get the keys set or generated in a
      previous set-keys or gen-keys request with deferred commitment..

   RETURN

      If the target principal and kvno correspond to uncommitted keys
      the server MUST respond with the actual keys that would be set by
      a subsequent commit-keys request.  Otherwise the server MUST
      respond with an error (meaning that this operation cannot be used
      to extract keys from the KDC that may be in use).

   ERRORS

         - generic
         - kvno-committed
         - no-such-kvno

3.2.7  Commit New Keys

   NAME

      commit-keys

   SYNOPSIS

      Req-commit-keys(kvno) ->
         Rep-commit-keys() |
         Err-commit-keys([help-text], error code, [error info])

   DESCRIPTION

      The commit-keys operation allows a client to bring a principal's
      new keys into use at the KDC.

      Clients SHOULD make a commit-keys request corresponding to a
      deferred commitment set-keys/gen-keys operation as soon as the
      local key database for the target principal is updated.

      The target principal name and the kvno MUST match those from a
      prior set-keys or gen-keys operation.

      Servers MAY expire delayed key commitments at will.  Servers
      SHOULD expire uncommitted new keys after a reasonable amount of
      time (600 seconds is RECOMMENDED).

      Servers MUST respond to new set-keys requests for principals with
      pending, uncommitted new keys by expiring the uncommitted new keys
      and proceeding as if there had been no expired new keys.

   ERRORS

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      - generic
      - new-keys-conflict (A set-keys or gen-keys request succeeded
                           subsequent to the request that matches this
                           {principal, kvno} tuple.)

3.2.8  Get Password Quality Policy

   NAME

      get-pw-policy

   SYNOPSIS

      Req-get-pw-policy() ->
         Rep-get-pw-policy([policy name], [policy description])

   DESCRIPTION

      Returns a description of the target principal's associated
      password quality policy, if any, as a list of localized
      UTF8String values.

      Clients can use this operation in conjunction with the change-pw
      operation to obtain text that can be displayed to the user before
      the user actually enters a new password.

      It is common for sites to set policies with respect to password
      quality.  It is beyond the scope of this document to describe such
      policies.  Management of password quality policies' actual content
      is also beyond the scope of this protocol.

   ERRORS

      No operation errors are defined.


3.2.9  Get Principal Aliases

   NAME

      get-print-aliases

   SYNOPSIS

      Req-get-princ-aliases() ->
         Rep-get-princ-aliases(aliases)

   DESCRIPTION

      Returns a list of aliases of the target principal.

   ERRORS

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      No operation-specific errors.

3.2.10  Get Realm's Supported Kerberos V Version and Features

   NAME

      get-realm-krb5-support

   SYNOPSIS

      Req-get-realm-krb5-support() ->
         Rep-get-realm-krb5-support(isupport)

   DESCRIPTION

      Returns set of Kerberos V features support by the target
      principal's realm's KDCs.

   ERRORS

      No operation-specific errors.

3.3  Principal Aliases

   Applications that use Kerberos often have to derive acceptor
   principal names from hostnames entered by users.  Such hostnames may
   be aliases, they may be fully qualified, partially qualified or not
   qualified at all.  Some implementations have resorted to deriving
   principal names from such hostnames by utilizing the names services
   to canonicalize the hostname first; such practices are not secure
   unless the name service are secure, which often aren't.

   One method for securely deriving principal names from hostnames is to
   alias principals at the KDC such that the KDC will issue tickets for
   principal names which are aliases of others.  It is helpful for
   principals to know what are their aliases as known by the KDCs.

   Note that changing a principal's aliases is out of scope for this
   protocol.

3.4  Kerberos V Feature Negotiation

   ...

4  ASN.1 Module

   DEFINITIONS EXPLICIT TAGS ::= BEGIN

   -- From [clarifications] with modifications
   PrincipalName            ::= SEQUENCE {
        name-string [1] SEQUENCE OF UTF8String
   }

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   Realm                    ::= UTF8String

   -- NOTE WELL: Principal and realm names MUST be constrained by the
   --            specification of the version of Kerberos V used by the
   --            client.
   --
   -- [Perhaps PrincipalName should be a SEQUENCE of an optional name
   --  type and a UTF8String, for simplicity.]

   -- From [clarifications]
   Int32            ::= INTEGER (-2147483648..2147483647)
   UInt32           ::= INTEGER (0..4294967295)

   -- Based on [clarifications]
   Etype            ::= Int32   -- as in [clarifications]
   Key      ::= SEQUENCE {
        enc-type        [0] Etype,      -- from Kerberos
        key             [1] OCTET STRING,
        ...
   }

   Language-Tag     ::= UTF8String -- Constrained by [RFC3066]

   -- Empty, extensible SEQUENCEs are legal ASN.1
   Extensible-NULL      ::= SEQUENCE {
        ...
   }

   -- Kerberos clients negotiate some parameters relating to their peers
   -- indirectly through the KDC.  Today this is true of ticket session
   -- key enctypes, but in the future this indirect negotiation may also
   -- occur with respect to the minor version of Kerberos V to be used
   -- between clients and servers.  Additionally, KDCs may need to know
   -- what authorization-data types are supported by service principals,
   -- both, for compatibility with legacy software and for optimization.
   --
   -- Thesefore it is important for KDCs to know what features of
   -- Kerberos V each service principal supports.
   --
   -- In version 2.0 of this protocol the clients and servers may notify
   -- each other of their support for:
   --
   --  - KerberosV minor version (rfc1510 -> 0, clarifications ->1)
   --  - enctypes
   --  - authorization data types
   --  - transited encoding data types
   --
   -- All authorization-data types defined in [clarifications] are
   -- assumed to be supported if the minor version is 1 and do not need
   -- to be included in the ad-type list.
   --
   -- Int32 is used for enctype and transited encoding data type
   -- identifiers.

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   --
   -- An extensible CHOICE of Int32 is used for authorization data
   -- types.

   KerberosV-TR-ID              ::= Int32

   KerberosV-AD-ID              ::= CHOICE {
        ad-int          [0] Int32,
        ...
   }

   KerberosVSupportNego ::= SEQUENCE {
        version         [0] ENUM {
                rfc1510,
                clarifications, -- replace with assigned RFC number
                -- add extensions
                ...
        }
        enc-types       [1] SEQUENCE OF Etype,
        ad-types        [2] SEQUENCE OF KerberosV-AD-ID OPTIONAL,
                                    -- authorization data types
        tr-enc-types    [3] SEQUENCE OF KerberosV-TR-ID OPTIONAL,
                                    -- transited encoding types
        ...
        -- A future extended Kerberos V may have optional features, in
        -- which case there might be an additional choice here, not of
        -- NULL, but of some other, possibly structured, type.
   }

   Request              ::= [APPLICATION 0] SEQUENCE {
        pvno-minor      [0] INTEGER DEFAULT 0,
        languages       [1] SEQUENCE OF Language-Tag OPTIONAL,
                -- Should be defaulted to the SEQUENCE of "i-default"
        targ-name       [2] PrincipalName OPTIONAL,
        targ-realm      [3] Realm OPTIONAL,
                -- If targ-name/realm are missing then the request
                -- applies to the principal of the client
        operation       [4] Op-req,
        ...
   }

   Response     ::= [APPLICATION 1] SEQUENCE {
        pvno-minor      [0] INTEGER DEFAULT 0,
        language        [1] Language-Tag DEFAULT "i-default",
        result          [2] Op-rep,
        ...
   }

   Error-Response       ::= [APPLICATION 2] SEQUENCE {
        pvno-minor      [0] INTEGER DEFAULT 0,
        language        [1] Language-Tag DEFAULT "i-default",
        error-code      [2] ProtocolErrorCode,
        help-text       [3] UTF8String OPTIONAL,

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        op-error        [4] Op-err OPTIONAL,
        ...
   }

   Op-req               ::= CHOICE {
        null                    [0] Req-null,
        change-pw               [1] Req-change-pw,
        set-pw                  [2] Req-set-pw,
        set-keys                [3] Req-set-keys,
        gen-keys                [4] Req-gen-keys,
        get-keys                [5] Req-get-keys,
        commit-keys             [6] Req-commit-keys,
        get-pw-policy           [7] Req-get-pw-policy,
        get-princ-aliases       [8] Req-get-princ-aliases,
        get-realm-krb5-support  [9] Req-get-realm-krb5-support,
        ...
   }

   Op-rep               ::= CHOICE {
        null                    [0] Rep-null,
        change-pw               [1] Rep-change-pw,
        set-pw                  [2] Rep-set-pw,
        set-keys                [3] Rep-set-keys,
        gen-keys                [4] Req-gen-keys,
        get-keys                [5] Req-get-keys,
        commit-keys             [6] Rep-commit-keys,
        get-pw-policy           [7] Rep-get-pw-policy,
        get-princ-aliases       [8] Rep-get-princ-aliases,
        get-realm-krb5-support  [9] Rep-get-realm-krb5-support,
        ...
   }

   Op-err       ::= CHOICE {
        null                    [0] Err-null,
        change-pw               [1] Err-change-pw,
        set-pw                  [2] Err-set-pw,
        set-keys                [3] Err-set-keys,
        gen-keys                [4] Err-gen-keys,
        get-keys                [5] Err-get-keys,
        commit-keys             [6] Err-commit-keys,
        get-pw-policy           [7] Err-get-pw-policy,
        get-princ-aliases       [8] Err-get-princ-aliases,
        get-realm-krb5-support  [9] Err-get-realm-krb5-support,
        ...
   }

   ProtocolErrorCode        ::= ENUM {
        proto-format-error,
        proto-unsupported-major-version,
        proto-unsupported-minor-version,
        proto-unsupported-operation,      -- Request CHOICE tag unknown
        proto-generic-see-op-error,       -- See Op-error
        proto-wrong-service-principal,    -- Use kadmin/setpw

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        proto-re-authentication-required,
        proto-initial-ticket-required,
        proto-client-and-target-realm-mismatch,
        proto-target-principal-unknown,
        proto-authorization-failed,
        ...
   }

   --
   -- Requests and responses
   --

   -- NULL request, much like ONC RPC's NULL procedure - NOT extensible
   Req-null    ::= NULL

   Rep-null    ::= NULL

   Err-null    ::= NULL

   -- Change password
   Req-change-pw        ::= SEQUENCE {
        old-pw          [0] UTF8String,
        new-pw          [1] UTF8String OPTIONAL,
        etypes          [2] SEQUENCE (1..) OF Etype OPTIONAL,
        ...
   }

   Rep-change-pw        ::= SEQUENCE {
        info-text       [0] UTF8String OPTIONAL,
        new-pw          [1] UTF8String OPTIONAL,
                                -- generated by the server if present
                                -- (and requested by the client)
        etypes          [2] SEQUENCE (1..) OF Etype OPTIONAL,
        ...
   }

   Err-change-pw        ::= SEQUENCE {
        help-text               [0] UTF8String OPTIONAL,
        error                   [1] CHOICE {
                op-generic-error                [0] Extensible-NULL,
                op-old-pw-incorrect             [1] Extensible-NULL,
                op-wont-generate-new-pw         [2] Extensible-NULL,
                op-new-pw-rejected-generic      [3] SEQUENCE {
                        policy              [1] SEQUENCE OF UTF8String,
                        suggested-pw        [2] UTF8String OPTIONAL,
                        ...
                }
                op-etype-not-supported          [4] SEQUENCE {
                        supported-etypes    [1] SEQUENCE OF Etype,
                        ...
                },
                ...
        },

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        ...
   }

   -- Set password
   Req-set-pw   ::= SEQUENCE {
        languages       [0] SEQUENCE OF Language-Tag OPTIONAL,
        new-pw          [1] UTF8String OPTIONAL,
        etypes          [2] SEQUENCE (1..) OF Etype OPTIONAL,
        ...
   }

   Rep-set-pw   ::= SEQUENCE {
        info-text       [0] UTF8String OPTIONAL,
        new-pw          [1] UTF8String OPTIONAL,
                                -- generated by the server if present
                                -- (and requested by the client)
        etypes          [2] SEQUENCE (1..) OF Etype OPTIONAL,
        ...
   }

   Err-set-pw   ::= SEQUENCE {
        help-text               [0] UTF8String OPTIONAL,
        error                   [1] CHOICE {
                op-generic-error                [0] Extensible-NULL,
                op-use-change-pw                [1] Extensible-NULL,
                op-wont-generate-new-pw         [2] Extensible-NULL,
                op-new-pw-rejected-generic      [3] SEQUENCE {
                        policy              [1] SEQUENCE OF UTF8String,
                        suggested-pw        [2] UTF8String OPTIONAL,
                        ...
                }
                op-etype-not-supported          [4] SEQUENCE {
                        supported-etypes    [1] SEQUENCE OF Etype,
                        ...
                },
                ...
        },
        ...
   }

   -- Set keys
   Req-set-keys ::= SEQUENCE {
        keys            [0] SEQUENCE OF Key,
        commit          [1] BOOLEAN,
                                -- TRUE  -> install keys now
                                --
                                -- FALSE -> require set-keys-commit
                                --          before issuing tickets
                                --          encrypted with these keys.
                                --
                                -- See commit-keys op
        isupport        [2] KerberosVSupportNego OPTIONAL,
                                -- For future Kerberos V extensions KDCs

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                                -- may need to know what krb5 version is
                                -- supported by individual service
                                -- principals.  This field provides a
                                -- way to tell the KDC what version of
                                -- Kerberos V the target principal
                                -- supports.
        ...
   }

   Rep-set-keys ::= SEQUENCE {
        info-text       [0] UTF8String OPTIONAL,
        kvno            [1] UInt32,
        aliases         [2] SEQUENCE OF SEQUENCE {
                name        [0] PrincipalName,
                realm       [1] Realm OPTIONAL,
                ...
        },
        isupport        [3] KerberosVSupportNego OPTIONAL,
        ...
        -- Should there be ETYPE-INFO2 stuff here?
   }

   Err-set-keys ::= SEQUENCE {
        help-text       [0] UTF8String OPTIONAL, -- Reason for rejection
        error           [1] CHOICE {
                op-generic                      [0] Extensible-NULL,
                op-deferred-commit-no-support   [1] Extensible-NULL,
                op-etype-no-support             [2] SEQUENCE OF {
                        supported-etypes        [1] SEQUENCE OF Etype,
                        ...
                }
                ...
        }
   }

   -- Generate keys
   Req-gen-keys ::= SEQUENCE {
        etypes          [0] SEQUENCE (1..) OF Etype,
        entropy         [1] OCTET STRING OPTIONAL,
        commit          [2] BOOLEAN,
                                -- TRUE  -> install keys now
                                --
                                -- FALSE -> require set-keys-commit
                                --          before issuing tickets
                                --          encrypted with these keys.
                                --
                                -- See commit-keys op
        isupport        [3] KerberosVSupportNego OPTIONAL,
                                -- For future Kerberos V extensions KDCs
                                -- may need to know what krb5 version is
                                -- supported by individual service
                                -- principals.  This field provides a
                                -- way to tell the KDC what version of

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                                -- Kerberos V the target principal
                                -- supports.
        ...
   }

   Rep-gen-keys ::= SEQUENCE {
        info-text       [0] UTF8String OPTIONAL,
        kvno            [1] UInt32,
        key             [2] Key,
        aliases         [3] SEQUENCE OF SEQUENCE {
                name        [0] PrincipalName,
                realm       [1] Realm OPTIONAL,
                ...
        },
        isupport        [4] KerberosVSupportNego OPTIONAL,
        ...
        -- Should there be ETYPE-INFO2 stuff here?
   }

   Err-gen-keys ::= Err-set-keys

   -- Get un-committed key request
   Req-get-keys ::= SEQUENCE {
        kvno            [0] UInt32,
        ...
   }

   Rep-get-keys ::= SEQUENCE {
        info-text       [0] UTF8String OPTIONAL,
        keys            [1] SEQUENCE OF Key,
        aliases         [2] SEQUENCE OF SEQUENCE {
                name        [0] PrincipalName,
                realm       [1] Realm OPTIONAL,
                ...
        },
        isupport        [3] KerberosVSupportNego OPTIONAL,
        ...
        -- Should there be ETYPE-INFO2 stuff here?
   }

   Err-get-keys ::= SEQUENCE {
        help-text       [0] UTF8String OPTIONAL, -- Reason for rejection
        error           [1] CHOICE {
                op-generic              [0] Extensible-NULL,
                op-kvno-committed       [1] Extensible-NULL,
                op-no-such-kvno         [1] Extensible-NULL,
                ...
        }
   }

   -- Commit a set keys request
   Req-commit-keys ::= SEQUENCE {
        kvno            [0] UInt32,

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        ...
   }

   Rep-commit-keys ::= Extensible-NULL

   Err-commit-keys ::= SEQUENCE {
        help-text       [0] UTF8String OPTIONAL, -- Reason for rejection
        error           [1] CHOICE {
                op-generic                  [0] Extensible-NULL,
                op-kvno-expired             [1] Extensible-NULL,
                    -- The client took too long to respond.
                op-kvno-unknown             [2] Extensible-NULL,
                    -- The targ princ/kvno is invalid or unknown to the
                    -- server (perhaps it lost track of state)
                op-new-keys-conflict        [3] Extensible-NULL,
                    -- A new-keys/commit-keys request subsequent to the
                    -- new-keys that produced the kvno has completed
                    -- and incremented the principal's kvno
                ...
        }
        ...
   }

   -- Get password policy
   Req-get-pw-policy   ::= Extensible-NULL

   Rep-get-pw-policy   ::= SEQUENCE {
        policy-name     [0] UTF8String OPTIONAL,
        description     [1] SEQUENCE OF UTF8String OPTIONAL,
        ...
   }

   Err-get-pw-policy   ::= Extensible-NULL

   -- Get principal aliases
   Req-get-princ-aliases        ::= Extensible-NULL

   Rep-get-princ-aliases        ::= SEQUENCE {
        help-text       [0] UTF8String OPTIONAL,
        aliases         [1] SEQUENCE OF SEQUENCE {
                name        [0] PrincipalName,
                realm       [1] Realm OPTIONAL,
                ...
        },
        ...
   }

   Err-get-princ-aliases        ::= Extensible-NULL

   -- Get list of enctypes supported by KDC for new keys
   Req-get-realm-krb5-support   ::=     Extensible-NULL

   Rep-get-realm-krb5-support   ::= SEQUENCE {

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        isupport        [0] KerberosVSupportNego,
                                -- Version of Kerberos V supported by
                                -- the target realm.
        ...
   }

   Err-get-realm-krb5-support   ::= Extensible-NULL

   END


6  IANA Considerations

   None.

7  Security Considerations

   Implementors and site administrators should note that the redundancy
   of UTF-8 encodings varies by Unicode codepoint used.  Password
   quality policies should, therefore, take this into account when
   estimating the amount of redundancy and entropy in a proposed new
   password.  [?? It's late at night - I think this is correct.]

   Kerberos set/change password/key protocol major version negotiation
   cannot be done securely.  A downgrade attack is possible against
   clients that attempt to negotiate the protocol major version to use
   with a server.  It is not clear at this time that the attacker would
   gain much from such a downgrade attack other than denial of service
   (DoS) by forcing the client to use a protocol version which does not
   support some feature needed by the client (Kerberos V in general is
   subject to a variety of DoS attacks anyways [RFC1510]).

   This protocol does not have Perfect Forward Security (PFS).  As a
   result, any passive network snooper watching password/key changing
   operations who has stolen a principal's password or long-term keys
   can find out what the new ones are.

   [More text needed]

8  Acknowledgements

   The authors would like to thank  Raeburn, Tom Yu, Martin Rex, Sam
   Hartman, Tony Andrea, Paul W. Nelson, Marcus Watts, Love, Joel N.
   Weber II, Jeffrey Hutzelman and other participants from the IETF
   Kerberos Working Group for their assistance.

9  References

9.1  Normative References

   [RFC2026]
      S. Bradner, RFC2026:  "The Internet Standard Process - Revision
      3," October 1996, Obsoletes - RFC 1602, Status: Best Current

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      Practice.

   [RFC2119]
      S. Bradner, RFC2119 (BCP14):  "Key words for use in RFCs to
      Indicate Requirement Levels," March 1997, Status: Best Current
      Practice.

   [X680]
      Abstract Syntax Notation One (ASN.1): Specification of Basic
      Notation, ITU-T Recommendation X.680 (1997) | ISO/IEC
      International Standard 8824-1:1998.
      http://www.itu.int/ITU-T/studygroups/com17/languages/X680_0702.pdf

   [X690]
      ASN.1 encoding rules: Specification of Basic Encoding Rules (BER),
      Canonical Encoding Rules (CER) and Distinguished Encoding Rules
      (DER), ITU-T Recommendation X.690 (1997)| ISO/IEC International
      Standard 8825-1:1998.
      http://www.itu.int/ITU-T/studygroups/com17/languages/X690_0702.pdf

   [clarifications]
      RFC-Editor: To be replaced by RFC number for draft-ietf-krb-wg-
      kerberos-clarifications.

   [k5stringprep]
      RFC-Editor: To be replaced by RFC number for draft-ietf-krb-wg-
      utf8-profile.

   [RFC3066]
      H. Alvestrand, RFC3066 (BCP47): "Tags for the Identification of
      Languages," January 2001, Obsoletes RFC1766, Status: Best Current
      Practice.

   [KPASSWDv1]
      (Reference needed!)

9.2  Informative References

   [RFC3244]
      M. Swift, J. Trostle, J. Brezak, RFC3244: "Microsoft Windows 2000
      Kerberos Change Password and Set Password Protocols," February
      2002, Status: Informational.

10  Authors' Addresses

      Nicolas Williams
      Sun Microsystems
      5300 Riata Trace Ct
      Austin, TX 78727
      Email: nicolas.williams@sun.com

      Jonathan Trostle
      Cisco Systems

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      170 W. Tasman Dr.
      San Jose, CA 95134
      Email: jtrostle@cisco.com

      Mike Swift
      University of Washington
      Seattle, WA
      Email: mikesw@cs.washington.edu

      John Brezak
      Microsoft
      1 Microsoft Way
      Redmond, WA 98052
      Email: jbrezak@microsoft.com

      Bill Gossman
      Cisco Systems
      500 108th Ave. NE, Suite 500
      Bellevue, WA 98004
      Email: bgossman@cisco.com

11  Notes to the RFC Editor

   This document has two KRB WG drafts as normative references and
   cannot progress until those drafts progress, but no other draft
   depends on this one.

Full Copyright Statement

   Copyright (C) The Internet Society (2003).  All Rights Reserved.

   This document and translations of it may be copied and furnished to
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   document itself may not be modified in any way, such as by removing
   the copyright notice or references to the Internet Society or other
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   The limited permissions granted above are perpetual and will not be
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   This document and the information contained herein is provided on an
   "AS IS" basis and THE INTERNET SOCIETY AND THE INTERNET ENGINEERING
   TASK FORCE DISCLAIMS 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

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   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.

Acknowledgement

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



















































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