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Network Working Group                                           M. SwiftRequest for Comments: 3244                      University of WashingtonCategory: Informational                                       J. Trostle                                                           Cisco Systems                                                               J. Brezak                                                               Microsoft                                                           February 2002Microsoft Windows 2000 Kerberos Change Passwordand Set Password ProtocolsStatus 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 20022.  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 theSwift, 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,                          targrealm[2]   Realm OPTIONAL                          }   The server must verify the AP-REQ message, check whether the client   principal in the ticket is authorized to set/change the password   (either for that principal, or for the principal in the targname   field if present), and decrypt the new password.  The server also   checks whether the initial flag is required for this request,   replying with status 0x0007 if it is not set and should be.  An   authorization failure is cause to respond with status 0x0005.  For   forward compatibility, the server should be prepared to ignore fields   after targrealm in the structure that it does not understand.   The newpasswd field contains the cleartext password, and the server   will apply any local policy checks including password policy checks.   The server then generates the appropriate keytypes from the password   and stores them in the KDC database.  If all goes well, status 0x0000   is returned to the client in the reply message (see below).   Reply 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_REP length        |         AP-REP 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.Swift, et al.                Informational                      [Page 3]

RFC 3244      Microsoft Windows 2000 Kerberos Change & Set February 2002   protocol version number: contains the hex constant 0x0001 (big-endian   integer). (The reply message has the same format as the original   change password protocol.)   AP-REP length: length of AP-REP data, in bytes.  If the length is   zero, then the last field contains a KRB-ERROR message instead of a   KRB-PRIV message.   AP-REP data: the AP-REP is the response to the AP-REQ in the request   packet.   KRB-PRIV message: This KRB-PRIV message must be encrypted with the   subsession key from the authenticator in the AP-REQ data.   The server will respond with a KRB-PRIV message unless it cannot   decode the client AP-REQ or KRB-PRIV message, in which case it will   respond with a KRB-ERROR message.  NOTE: Unlike change password   version 1, the KRB-ERROR message will be sent back without any   encapsulation.   The user-data component of the KRB-PRIV message, or e-data component   of the KRB-ERROR message, consists of the following data.     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    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+    |          result code          |        result string          /    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+   result code (16 bits) (result codes 0-4 are from the original change   password protocol):      The result code must have one of the following values      (big-endian integer):      KRB5_KPASSWD_SUCCESS             0 request succeeds (This value                                         is not allowed in a KRB-ERROR                                         message)      KRB5_KPASSWD_MALFORMED           1 request fails due to being                                         malformed      KRB5_KPASSWD_HARDERROR           2 request fails due to "hard"                                         error in processing the                                         request (for example, there                                         is a resource or other                                         problem causing the request                                         to fail)Swift, et al.                Informational                      [Page 4]

RFC 3244      Microsoft Windows 2000 Kerberos Change & Set February 2002      KRB5_KPASSWD_AUTHERROR           3 request fails due to an error                                         in authentication processing      KRB5_KPASSWD_SOFTERROR           4 request fails due to a                                         "soft" error in processing                                         the request      KRB5_KPASSWD_ACCESSDENIED        5 requestor not authorized      KRB5_KPASSWD_BAD_VERSION         6 protocol version unsupported      KRB5_KPASSWD_INITIAL_FLAG_NEEDED 7 initial flag required      0xFFFF is returned if the request fails for some other reason.      Although only a few non-zero result codes are specified here, the      client should accept any non-zero result code as indicating      failure.   result string:      This field contains information which might be useful to the user,      such as feedback about policy failures.  The string is encoded in      UTF-8.  It may be omitted if the server does not wish to include      it.  If it is present, the client will display the string to the      user.3. Security Considerations   Password policies should be enforced to make sure that users do not   pick passwords (for change password) that are vulnerable to brute   force password guessing attacks.  An administrator who is authorized   to set other principal's passwords is highly trusted and must also   carefully protect his/her own credentials.4.  References   [1]   Kohl, J. and C. Neuman, "The Kerberos Network Authentication         Service (V5)",RFC 1510, September 1993.Swift, et al.                Informational                      [Page 5]

RFC 3244      Microsoft Windows 2000 Kerberos Change & Set February 20025. Authors' Addresses   Mike Swift   University of Washington   Seattle, WA   EMail: mikesw@cs.washington.edu   Jonathan Trostle   Cisco Systems   170 W. Tasman Dr.   San Jose, CA 95134   EMail: john3725@world.std.com   John Brezak   Microsoft   1 Microsoft Way   Redmond, WA 98052   EMail: jbrezak@microsoft.comSwift, et al.                Informational                      [Page 6]

RFC 3244      Microsoft Windows 2000 Kerberos Change & Set February 20026.  Full Copyright Statement   Copyright (C) The Internet Society (2002).  All Rights Reserved.   This document and translations of it may be copied and furnished to   others, and derivative works that comment on or otherwise explain it   or assist in its implementation may be prepared, copied, published   and distributed, in whole or in part, without restriction of any   kind, provided that the above copyright notice and this paragraph are   included on all such copies and derivative works.  However, this   document itself may not be modified in any way, such as by removing   the copyright notice or references to the Internet Society or other   Internet organizations, except as needed for the purpose of   developing Internet standards in which case the procedures for   copyrights defined in the Internet Standards process must be   followed, or as required to translate it into languages other than   English.   The limited permissions granted above are perpetual and will not be   revoked by the Internet Society or its successors or assigns.   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   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.Acknowledgement   Funding for the RFC Editor function is currently provided by the   Internet Society.Swift, et al.                Informational                      [Page 7]