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7Network Working Group                                           M. Swift
8Request for Comments: 3244                      University of Washington
9Category: Informational                                       J. Trostle
10                                                           Cisco Systems
11                                                               J. Brezak
12                                                               Microsoft
13                                                           February 2002
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15
16            Microsoft Windows 2000 Kerberos Change Password
17                       and Set Password Protocols
18
19Status of this Memo
20
21   This memo provides information for the Internet community.  It does
22   not specify an Internet standard of any kind.  Distribution of this
23   memo is unlimited.
24
25Copyright Notice
26
27   Copyright (C) The Internet Society (2002).  All Rights Reserved.
28
29Abstract
30
31   This memo specifies Microsoft's Windows 2000 Kerberos change password
32   and set password protocols.  The Windows 2000 Kerberos change
33   password protocol interoperates with the original Kerberos change
34   password protocol.  Change password is a request reply protocol that
35   includes a KRB_PRIV message that contains the new password for the
36   user.
37
381. Introduction
39
40   Microsoft's Windows 2000 Kerberos change password protocol
41   interoperates with the original Kerberos change password protocol.
42   Change password is a request reply protocol that includes a KRB_PRIV
43   message that contains the new password for the user.  The original
44   change password protocol does not allow an administrator to set a
45   password for a new user.  This functionality is useful in some
46   environments, and this proposal extends the change password protocol
47   to allow password setting.  The changes are: adding new fields to the
48   request message to indicate the principal which is having its
49   password set, not requiring the initial flag in the service ticket,
50   using a new protocol version number, and adding three new result
51   codes.
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60RFC 3244      Microsoft Windows 2000 Kerberos Change & Set February 2002
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632.  The Protocol
64
65   The service accepts requests on UDP port 464 and TCP port 464 as
66   well.  The protocol consists of a single request message followed by
67   a single reply message.  For UDP transport, each message must be
68   fully contained in a single UDP packet.
69
70   For TCP transport, there is a 4 octet header in network byte order
71   that precedes the message and specifies the length of the message.
72
73   Request Message
74
75     0                   1                   2                   3
76     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
77    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
78    |         message length        |    protocol version number    |
79    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
80    |          AP_REQ length        |         AP_REQ data           /
81    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
82    /                        KRB-PRIV message                       /
83    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
84
85   All 16 bit fields are in big-endian order.
86
87   message length field: contains the number of bytes in the message
88   including this field.
89
90   protocol version number: contains the hex constant 0xff80 (big-endian
91   integer).
92
93   AP-REQ length: length of AP-REQ data, in bytes.  If the length is
94   zero, then the last field contains a KRB-ERROR message instead of a
95   KRB-PRIV message.
96
97   AP-REQ data: (see [1]) The AP-REQ message must be for the service
98   principal kadmin/changepw@REALM, where REALM is the REALM of the user
99   who wishes to change/set his password.  The authenticator in the AP-
100   REQ must include a subsession key.  (NOTE: The subsession key must be
101   pseudo-randomly generated and must never be reused for multiple
102   authenticators.)  To enable setting of passwords, it is not required
103   that the initial flag be set in the Kerberos service ticket.
104
105   KRB-PRIV message (see [1]) This user-data field in the KRB-PRIV
106   message is encrypted using the subkey from the authenticator in the
107   AP-REQ data.  The usec and seq-number fields of the KRB_PRIV message
108   are present and have the same value as the seq-number field in the
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116RFC 3244      Microsoft Windows 2000 Kerberos Change & Set February 2002
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119   authenticator from the AP_REQ message (the seq-number in the
120   authenticator will be present).  The server ignores the optional
121   r-address field in the KRB_PRIV message, if it is present.
122
123   The user-data component of the message consists of the following
124   ASN.1 structure encoded as an OCTET STRING:
125
126      ChangePasswdData ::=  SEQUENCE {
127                          newpasswd[0]   OCTET STRING,
128                          targname[1]    PrincipalName OPTIONAL,
129                          targrealm[2]   Realm OPTIONAL
130                          }
131
132   The server must verify the AP-REQ message, check whether the client
133   principal in the ticket is authorized to set/change the password
134   (either for that principal, or for the principal in the targname
135   field if present), and decrypt the new password.  The server also
136   checks whether the initial flag is required for this request,
137   replying with status 0x0007 if it is not set and should be.  An
138   authorization failure is cause to respond with status 0x0005.  For
139   forward compatibility, the server should be prepared to ignore fields
140   after targrealm in the structure that it does not understand.
141
142   The newpasswd field contains the cleartext password, and the server
143   will apply any local policy checks including password policy checks.
144   The server then generates the appropriate keytypes from the password
145   and stores them in the KDC database.  If all goes well, status 0x0000
146   is returned to the client in the reply message (see below).
147
148   Reply Message
149
150     0                   1                   2                   3
151     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
152    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
153    |         message length        |    protocol version number    |
154    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
155    |          AP_REP length        |         AP-REP data           /
156    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
157    /                         KRB-PRIV message                      /
158    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
159
160   All 16 bit fields are in big-endian order.
161
162   message length field: contains the number of bytes in the message
163   including this field.
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175   protocol version number: contains the hex constant 0x0001 (big-endian
176   integer). (The reply message has the same format as the original
177   change password protocol.)
178
179   AP-REP length: length of AP-REP data, in bytes.  If the length is
180   zero, then the last field contains a KRB-ERROR message instead of a
181   KRB-PRIV message.
182
183   AP-REP data: the AP-REP is the response to the AP-REQ in the request
184   packet.
185
186   KRB-PRIV message: This KRB-PRIV message must be encrypted with the
187   subsession key from the authenticator in the AP-REQ data.
188
189   The server will respond with a KRB-PRIV message unless it cannot
190   decode the client AP-REQ or KRB-PRIV message, in which case it will
191   respond with a KRB-ERROR message.  NOTE: Unlike change password
192   version 1, the KRB-ERROR message will be sent back without any
193   encapsulation.
194
195   The user-data component of the KRB-PRIV message, or e-data component
196   of the KRB-ERROR message, consists of the following data.
197
198     0                   1                   2                   3
199     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
200    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
201    |          result code          |        result string          /
202    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
203
204   result code (16 bits) (result codes 0-4 are from the original change
205   password protocol):
206
207      The result code must have one of the following values
208      (big-endian integer):
209
210      KRB5_KPASSWD_SUCCESS             0 request succeeds (This value
211                                         is not allowed in a KRB-ERROR
212                                         message)
213
214      KRB5_KPASSWD_MALFORMED           1 request fails due to being
215                                         malformed
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217      KRB5_KPASSWD_HARDERROR           2 request fails due to "hard"
218                                         error in processing the
219                                         request (for example, there
220                                         is a resource or other
221                                         problem causing the request
222                                         to fail)
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231      KRB5_KPASSWD_AUTHERROR           3 request fails due to an error
232                                         in authentication processing
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234      KRB5_KPASSWD_SOFTERROR           4 request fails due to a
235                                         "soft" error in processing
236                                         the request
237
238      KRB5_KPASSWD_ACCESSDENIED        5 requestor not authorized
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240      KRB5_KPASSWD_BAD_VERSION         6 protocol version unsupported
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242      KRB5_KPASSWD_INITIAL_FLAG_NEEDED 7 initial flag required
243
244      0xFFFF is returned if the request fails for some other reason.
245      Although only a few non-zero result codes are specified here, the
246      client should accept any non-zero result code as indicating
247      failure.
248
249   result string:
250
251      This field contains information which might be useful to the user,
252      such as feedback about policy failures.  The string is encoded in
253      UTF-8.  It may be omitted if the server does not wish to include
254      it.  If it is present, the client will display the string to the
255      user.
256
2573. Security Considerations
258
259   Password policies should be enforced to make sure that users do not
260   pick passwords (for change password) that are vulnerable to brute
261   force password guessing attacks.  An administrator who is authorized
262   to set other principal's passwords is highly trusted and must also
263   carefully protect his/her own credentials.
264
2654.  References
266
267   [1]   Kohl, J. and C. Neuman, "The Kerberos Network Authentication
268         Service (V5)", RFC 1510, September 1993.
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2875. Authors' Addresses
288
289   Mike Swift
290   University of Washington
291   Seattle, WA
292
293   EMail: mikesw@cs.washington.edu
294
295
296   Jonathan Trostle
297   Cisco Systems
298   170 W. Tasman Dr.
299   San Jose, CA 95134
300
301   EMail: john3725@world.std.com
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304   John Brezak
305   Microsoft
306   1 Microsoft Way
307   Redmond, WA 98052
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309   EMail: jbrezak@microsoft.com
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3436.  Full Copyright Statement
344
345   Copyright (C) The Internet Society (2002).  All Rights Reserved.
346
347   This document and translations of it may be copied and furnished to
348   others, and derivative works that comment on or otherwise explain it
349   or assist in its implementation may be prepared, copied, published
350   and distributed, in whole or in part, without restriction of any
351   kind, provided that the above copyright notice and this paragraph are
352   included on all such copies and derivative works.  However, this
353   document itself may not be modified in any way, such as by removing
354   the copyright notice or references to the Internet Society or other
355   Internet organizations, except as needed for the purpose of
356   developing Internet standards in which case the procedures for
357   copyrights defined in the Internet Standards process must be
358   followed, or as required to translate it into languages other than
359   English.
360
361   The limited permissions granted above are perpetual and will not be
362   revoked by the Internet Society or its successors or assigns.
363
364   This document and the information contained herein is provided on an
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367   BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF THE INFORMATION
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369   MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
370
371Acknowledgement
372
373   Funding for the RFC Editor function is currently provided by the
374   Internet Society.
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