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Versions: 00 01 02 03 04 05 06                                          
INTERNET-DRAFT                                        Mike Swift
draft-ietf-cat-kerberos-set-passwd-04.txt             University of WA
March 2001                                            Jonathan Trostle
                                                      Cisco Systems
                                                      John Brezak
                                                      Microsoft
                                                      Bill Gossman
                                                      Cybersafe

              Kerberos Set/Change Password: Version 2


0. Status Of This Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   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.

   Comments and suggestions on this document are encouraged.  Comments
   on this document should be sent to the CAT working group discussion
   list: ietf-cat-wg@stanford.edu.

   This draft expires on September 30th, 2001.

1. Abstract

   The Kerberos (RFC 1510 [3]) change password protocol (Horowitz [4]),
   does not allow for an administrator to set a password for a new user.
   This functionality is useful in some environments, and this proposal
   extends [4] 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. We also extend the set/change protocol to allow a
   client to send a sequence of keys to the KDC instead of a cleartext
   password. If in the cleartext password case, the cleartext password
   fails to satisfy password policy, the server should use the result
   code KRB5_KPASSWD_POLICY_REJECT.

2. 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 RFC-2119 [2].

3. The Protocol

   The service MUST accept 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
   precedes the message and specifies the length of the message. This
   requirement is consistent with the TCP transport header in 1510bis.

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 network byte order.

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

   protocol version number: contains the hex constant 0x0002 (network
   byte order).

   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 [3]) For a change password/key request, the AP-REQ
   message service ticket sname, srealm principal identifier is
   kadmin/changepw@REALM where REALM is the realm of the change password
   service. The same applies to a set password/key request except the
   principal identifier is kadmin/setpw@REALM. To enable setting of
   passwords/keys, it is not required that the initial flag be set in the
   Kerberos service ticket. The initial flag is required for change requests,
   but not for set requests. We have the following definitions:

                    old passwd   initial flag  target principal can be
                    in request?  required?     distinct from
                                               authenticating principal?

   change password:  yes         yes           no

   set password:     no          policy (*)    yes

   set key:          no          policy (*)    yes

   change key:       no          yes           no

   policy (*): implementations SHOULD allow administrators to set the
   initial flag required for set requests policy to either yes or no.
   Clients MUST be able to retry set requests that fail due to error 7
   (initial flag required) with an initial ticket. Clients SHOULD NOT
   cache service tickets targetted at kadmin/changepw.

   KRB-PRIV message (see [3]) This KRB-PRIV message must be encrypted
   using the session key from the ticket in the AP-REQ.

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

   ChangePasswdData :: =  SEQUENCE {
                       newpasswdorkeys[0]   NewPasswdOrKeys,
                       targname[1]          PrincipalName OPTIONAL,
                         -- only present in set password/key: the principal
                         -- which will have its password or keys set. Not
                         -- present in a set request if the client principal
                         -- from the ticket is the principal having its
                         -- passwords or keys set.
                       targrealm[2]         Realm OPTIONAL,
                         -- only present in set password/key: the realm for
                         -- the principal which will have its password or
                         -- keys set. Not present in a set request if the
                         -- client principal from the ticket is the principal
                         -- having its passwords or keys set.
                       flags[3]             RequestFlags OPTIONAL
                         -- 32 bit string
                       }

   NewPasswdOrKeys :: = CHOICE {
                       passwords[0]  PasswordSequence,  -- change/set passwd
                       keyseq[1]     KeySequences       -- change/set key
   }

   KeySequences :: = SEQUENCE OF KeySequence

   KeySequence :: = SEQUENCE {
                       key[0]        EncryptionKey,
                       salt[1]       OCTET STRING OPTIONAL,
                       salt-type[2]  INTEGER OPTIONAL
   }

   PasswordSequence :: = SEQUENCE {
                       newpasswd[0]  OCTET STRING,
                       oldpasswd[1]  OCTET STRING OPTIONAL
                         -- oldpasswd always present for change password
                         -- but not present for set password, set key, or
                         -- change key
   }

   RequestFlags :: = BIT STRING {
                     reserved(0),
                     request-srv-gen-keys(1)  -- only in change/set keys
                                              -- if the client desires
                                              -- server to contribute to keys;
                                              -- server will return keys
                     }

   The server must verify the AP-REQ message, check whether the client
   principal in the ticket is authorized to set or change the password
   (either for that principal, or for the principal in the targname
   field if present), and decrypt the new password/keys. 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 newpasswdorkeys field contains either the new cleartext password
   (with the old cleartext password for a change password operation),
   or a sequence of encryption keys with their respective salts.

   In the cleartext password case, if the old password is sent in the
   request, the request MUST be a change password request. If the old
   password is not present in the request, the request MUST be a set
   password request. The server should apply policy checks to the old
   and new password after verifying that the old password is valid.
   The server can check validity by obtaining a key from the old
   password with a keytype that is present in the KDC database for the
   user and comparing the keys for equality. 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). For a change password operation,
   the initial flag in the service ticket MUST be set.

   In the key sequence case, the sequence of keys is sent to the change
   or set password service (kadmin/changepw or kadmin/setpw respectively).
   For a principal that can act as a server, its preferred keytype should
   be sent as the first key in the sequence, but the KDC is not required
   to honor this preference. Application servers should use the key
   sequence option for changing/setting their keys. The change/set password
   services should check that all keys are in the proper format, returning
   the KRB5_KPASSWD_MALFORMED error otherwise.

   For change/set key, the request message may include the request flags bit
   string with the request-srv-gen-keys bit set. In this case, the client
   is requesting that the server add entropy to its keys in the KeySequences
   field. When using this option, the client SHOULD attempt to generate
   pseudorandom keys with as much entropy as possible in its request. The
   server will return the final key sequence in a KeySequences structure in
   the edata of the reply message. The server does not store any of the

   new keys at this point. The client MUST make a subsequent change/set
   key request without the request-srv-gen-keys bit; if the server returns
   KRB5_KPASSWD_SUCCESS for this second request, then the new keys have
   been written into the database. A conformant server MUST support this
   option.

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 network byte order.

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

   protocol version number: contains the hex constant 0x0002 (network
   byte order). (The reply message has the same format as in [4]).

   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. An implementation should check this field to determine
   whether a KRB-ERROR message or KRB-PRIV message has been returned.

   AP-REP data: the AP-REP is the response to the AP-REQ in the request
   packet.

   KRB-PRIV from [4]: This KRB-PRIV message must be encrypted using the
   session key from the ticket in the AP-REQ.

   The server will respond with a KRB-PRIV message unless it cannot
   validate the client AP-REQ or KRB-PRIV message, in which case it will
   respond with a KRB-ERROR message.

   The user-data component of the KRB-PRIV message, or e-data component
   of the KRB-ERROR message, must consist 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          |        minor status           |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | key version (only on success) |        edata                  /
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      result code (16 bits) (result codes 0-4 are from [4]):
         The result code must have one of the following values (network
         byte order):

         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)

         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_INITIALFLAG_NEEDED 7 initial flag required

         KRB5_KPASSWD_POLICY_REJECT      8 new cleartext password fails
                                           policy; the result string should
                                           include a text message to be
                                           presented to the user.

         KRB5_KPASSWD_BAD_PRINCIPAL      9 target principal does not exist
                                           (only in response to a set
                                           password or set key request).

         KRB5_KPASSWD_ETYPE_NOSUPP 10 the request contains a key sequence
                                      containing at least one etype that is
                                      not supported by the KDC. The response
                                      edata contains an ASN.1 encoded
                                      PKERB-ETYPE-INFO type that specifies
                                      the etypes that the KDC supports:

                                      KERB-ETYPE-INFO-ENTRY :: = SEQUENCE {
                                         encryption-type[0]  INTEGER,
                                         salt[1]        OCTET STRING
                                               OPTIONAL -- not sent, client
                                                       -- ignores if sent
                                      }

                                      PKERB-ETYPE-INFO ::= SEQUENCE OF
                                                      KERB-ETYPE-INFO-ENTRY

                                      The client should retry the request
                                      using only etypes (keytypes) that are
                                      contained within the PKERB-ETYPE-INFO
                                      structure in the previous response.

         KRB5_KPASSWD_ETYPE_SRVGENKEYS 11 the request has the request-
                                          srv-gen-keys flag set and the
                                          server is returning the
                                          KeySequence structure defined
                                          above in the edata field of the
                                          reply. The server returns one key

                                          sequence structure of the same
                                          keytype for each key sequence
                                          structure in the client request,
                                          unless it does not support one of
                                          the keytypes (or etypes). In that
                                          case, it returns error
                                          KRB5_KPASSWD_ETYPE_NOSUPP as
                                          discussed above. The server MUST
                                          add keylength number of bits of
                                          entropy to each key. The assumption
                                          here is that the client may have
                                          added insufficient entropy to the
                                          request keys. The server SHOULD use
                                          the client key from each
                                          KeySequence structure as input
                                          into the final keyvalue for the
                                          returned key.

         0xFFFF is returned if the request fails for some other reason.
         The client must interpret any non-zero result code as a failure.
      minor status (16 bits):
         This field contains a minor status code. It can be used to index
         into a catalog of strings and the indexed string can then be
         displayed to the user. Additional information on a password
         set/change policy failure is one use for this string.
      key version (16 bits - optional): present if and only if the result
         code is KRB5_KPASSWD_SUCCESS. This contains the key version of
         the new key(s).
      edata: used to convey additional information as defined by the
         result code.

4. Acknowledgements

   The authors thank Tony Andrea for his input to the document.

5. References

   [1] Bradner, S., "The Internet Standards Process -- Revision 3", BCP
       9, RFC 2026, October 1996.

   [2] Bradner, S., "Key words for use in RFCs to Indicate Requirement
       Levels", BCP 14, RFC 2119, March 1997

   [3] J. Kohl, C. Neuman. The Kerberos Network Authentication
       Service (V5), Request for Comments 1510.

   [4] M. Horowitz. Kerberos Change Password Protocol,
       ftp://ds.internic.net/internet-drafts/
       draft-ietf-cat-kerb-chg-password-02.txt

6. Expiration Date

   This draft expires on September 30th, 2001.

7. Authors' Addresses

   Jonathan Trostle
   Cisco Systems
   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
   1 Microsoft Way
   Redmond, WA 98052
   Email: jbrezak@microsoft.com

   Bill Gossman
   Cybersafe Corporation
   1605 NW Sammamish Rd.
   Issaquah, WA 98027-5378
   Email: bill.gossman@cybersafe.com