Microsoft Windows 2000 Kerberos Change Password and Set Password Protocols
RFC 3244

Document Type RFC - Informational (February 2002; No errata)
Last updated 2013-03-02
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Network Working Group                                           M. Swift
Request for Comments: 3244                      University of Washington
Category: Informational                                       J. Trostle
                                                           Cisco Systems
                                                               J. Brezak
                                                               Microsoft
                                                           February 2002

            Microsoft Windows 2000 Kerberos Change Password
                       and Set Password Protocols

Status of this Memo

   This memo provides information for the Internet community.  It does
   not specify an Internet standard of any kind.  Distribution of this
   memo is unlimited.

Copyright Notice

   Copyright (C) The Internet Society (2002).  All Rights Reserved.

Abstract

   This memo specifies Microsoft's Windows 2000 Kerberos change password
   and set password protocols.  The Windows 2000 Kerberos change
   password protocol interoperates with the original Kerberos change
   password protocol.  Change password is a request reply protocol that
   includes a KRB_PRIV message that contains the new password for the
   user.

1. Introduction

   Microsoft's Windows 2000 Kerberos change password protocol
   interoperates with the original Kerberos change password protocol.
   Change password is a request reply protocol that includes a KRB_PRIV
   message that contains the new password for the user.  The original
   change password protocol does not allow an administrator to set a
   password for a new user.  This functionality is useful in some
   environments, and this proposal extends the change password protocol
   to allow password setting.  The changes are: adding new fields to the
   request message to indicate the principal which is having its
   password set, not requiring the initial flag in the service ticket,
   using a new protocol version number, and adding three new result
   codes.

Swift, et al.                Informational                      [Page 1]
RFC 3244      Microsoft Windows 2000 Kerberos Change & Set February 2002

2.  The Protocol

   The service accepts requests on UDP port 464 and TCP port 464 as
   well.  The protocol consists of a single request message followed by
   a single reply message.  For UDP transport, each message must be
   fully contained in a single UDP packet.

   For TCP transport, there is a 4 octet header in network byte order
   that precedes the message and specifies the length of the message.

   Request 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    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |          AP_REQ length        |         AP_REQ data           /
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    /                        KRB-PRIV message                       /
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   All 16 bit fields are in big-endian order.

   message length field: contains the number of bytes in the message
   including this field.

   protocol version number: contains the hex constant 0xff80 (big-endian
   integer).

   AP-REQ length: length of AP-REQ data, in bytes.  If the length is
   zero, then the last field contains a KRB-ERROR message instead of a
   KRB-PRIV message.

   AP-REQ data: (see [1]) The AP-REQ message must be for the service
   principal kadmin/changepw@REALM, where REALM is the REALM of the user
   who wishes to change/set his password.  The authenticator in the AP-
   REQ must include a subsession key.  (NOTE: The subsession key must be
   pseudo-randomly generated and must never be reused for multiple
   authenticators.)  To enable setting of passwords, it is not required
   that the initial flag be set in the Kerberos service ticket.

   KRB-PRIV message (see [1]) This user-data field in the KRB-PRIV
   message is encrypted using the subkey from the authenticator in the
   AP-REQ data.  The usec and seq-number fields of the KRB_PRIV message
   are present and have the same value as the seq-number field in the

Swift, et al.                Informational                      [Page 2]
RFC 3244      Microsoft Windows 2000 Kerberos Change & Set February 2002

   authenticator from the AP_REQ message (the seq-number in the
   authenticator will be present).  The server ignores the optional
   r-address field in the KRB_PRIV message, if it is present.

   The user-data component of the message consists of the following
   ASN.1 structure encoded as an OCTET STRING:

      ChangePasswdData ::=  SEQUENCE {
                          newpasswd[0]   OCTET STRING,
                          targname[1]    PrincipalName OPTIONAL,
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