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Versions: 00 01

Network Working Group                                            G. Zorn
Internet-Draft                                     Microsoft Corporation
Category: Informational                                    November 1997
<draft-ietf-radius-mschap-attr-01.txt>

                 RADIUS Attributes for MS-CHAP Support


1.  Status of this Memo

This  document  is an Internet-Draft.  Internet-Drafts are working docu-
ments of the Internet Engineering Task Force (IETF), its areas, and  its
working groups.  Note that other groups may also distribute working doc-
uments 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''.

To  learn  the  current  status  of any Internet-Draft, please check the
``1id-abstracts.txt'' listing contained in  the  Internet-Drafts  Shadow
Directories  on ds.internic.net (US East Coast), nic.nordu.net (Europe),
ftp.isi.edu (US West Coast), or munnari.oz.au (Pacific Rim).

This memo provides information for the Internet  community.   This  memo
does  not specify an Internet standard of any kind.  The distribution of
this memo is  unlimited.   It  is  filed  as  <draft-ietf-radius-mschap-
attr-01.txt>  and  expires  May  21,  1998.  Please send comments to the
RADIUS Working Group mailing list (ietf-radius@livingston.com) or to the
author (glennz@microsoft.com).


2.  Abstract

This  document  describes  a  set  of  vendor-specific RADIUS attributes
designed to support the use of Microsoft's proprietary  dialect  of  PPP
CHAP  (MS-CHAP) in dial-up networks.  MS-CHAP is derived from and (where
possible) consistent with PPP CHAP [1]; the differences between PPP CHAP
and  MS-CHAP  are  significant  enough  to warrant the definition of new
RADIUS attributes, however.


3.  Introduction

Microsoft created Microsoft Challenge-Handshake Authentication  Protocol
(MS-CHAP)  to  authenticate  remote  Windows workstations, providing the
functionality to which LAN-based users are accustomed.  Where  possible,



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MS-CHAP is consistent with standard CHAP, and the differences are easily
modularized.  Briefly, the differences between MS-CHAP and standard CHAP
are:

   * MS-CHAP is enabled by negotiating CHAP Algorithm 0x80 in LCP
     option 3, Authentication Protocol.

   * The MS-CHAP Response packet is in a format designed for
     compatibility with Microsoft Windows NT 3.5, 3.51 and 4.0,
     Microsoft Windows95, and Microsoft LAN Manager 2.x networking
     products.  The MS-CHAP format does not require the
     authenticator to store a clear-text or reversibly encrypted
     password.

   * MS-CHAP provides an authenticator-controlled authentication
     retry mechanism.

   * MS-CHAP provides an authenticator-controlled password changing
     mechanism.

   * MS-CHAP defines an extended  set of reason-for-failure codes,
     returned in the Failure packet Message field.

The attributes defined in this document reflect these differences.


4.  Specification of Requirements

In  this  document,  the key words "MAY", "MUST, "MUST NOT", "optional",
"recommended", "SHOULD", and "SHOULD  NOT"  are  to  be  interpreted  as
described in [2].


5.  Attributes

The  following sections describe sub-attributes which may be transmitted
in one or more RADIUS attributes of type Vendor-Specific [3].  More than
one  sub-attribute  MAY  be  transmitted  in  a  single  Vendor-Specific
Attribute; if this is done, the sub-attributes SHOULD  be  packed  as  a
sequence of Vendor-Type/Vendor-Length/Value triples following the inital
Type, Length and Vendor-ID fields.  The Length field of the  Vendor-Spe-
cific Attribute MUST be set equal to the sum of the Vendor-Length fields
of the sub-attributes contained in the Vendor-Specific  Attribute,  plus
six.   The  Vendor-ID  field of the Vendor-Specific Attribute(s) MUST be
set to decimal 311 (Microsoft).






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5.1.  MS-CHAP-Challenge

   Description

      This Attribute contains the challenge sent by a NAS to a Microsoft
      Challenge-Handshake  Authentication  Protocol  (MS-CHAP) user.  It
      MAY be used in both Access-Request and Access-Challenge packets.

   A summary of the MS-CHAP-Challenge Attribute format is  shown  below.
   The fields are transmitted from left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vendor-Type | Vendor-Length |           String...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Vendor-Type
      11 for MS-CHAP-Challenge.

   Vendor-Length
      > 2

   String
      The String field contains the MS-CHAP challenge.


5.2.  MS-CHAP-Response

   Description

      This  Attribute  contains  the  response  value  provided by a PPP
      Microsoft Challenge-Handshake  Authentication  Protocol  (MS-CHAP)
      user  in  response  to  the challenge.  It is only used in Access-
      Request packets.

   A summary of the MS-CHAP-Response Attribute format  is  shown  below.
   The fields are transmitted from left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |  Vendor-Type  | Vendor-Length |    Ident    |     Flags     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           LM-Response
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            LM-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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                            LM-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            LM-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            LM-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            LM-Response(cont)                    |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                           NT-Response
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            NT-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            NT-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            NT-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            NT-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            NT-Response (cont)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Vendor-Type
      1 for MS-CHAP-Response.

   Vendor-Length
      52

   Ident
      Identical to the PPP CHAP Identifier.

   Flags
      The Flags field is one octet in length.  If the Flags field is one
      (0x01), the NT-Response field is to be used in preference  to  the
      LM-Response  field  for authentication.  The LM-Response field MAY
      still be used (if non-empty), but the NT-Response SHOULD be  tried
      first.   If  it is zero, the NT-Response field MUST be ignored and
      the LM-Response field used.

   LM-Response
      The LM-Response field is 24 octets in length and holds an  encoded
      function  of  the  password  and  the received challenge.  If this
      field is empty, it SHOULD be zero-filled.

   NT-Response
      The NT-Response field is 24 octets in length and holds an  encoded
      function  of  the  password  and  the received challenge.  If this
      field is empty, it SHOULD be zero-filled.




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5.3.  MS-CHAP-Domain

   Description

      The MS-CHAP-Domain Attribute indicates the Windows  NT  domain  in
      which  the  user  was  authenticated.   It MAY be included in both
      Access-Accept and Accounting-Request packets.

   A summary of the MS-CHAP-Domain Attribute format is given below.  The
   fields are transmitted left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vendor-Type | Vendor-Length |     Ident     |    String...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Vendor-Type
      10 for MS-CHAP-Domain.

   Vendor-Length
      > 3

   Ident
      The  Ident  field  is  one octet and aids in matching requests and
      replies.

   String
      This field contains the name in ASCII of the Windows NT domain  in
      which the user was authenticated.


5.4.  MS-CHAP-Error

   Description

      The  MS-CHAP-Error  Attribute  contains  error data related to the
      preceding MS-CHAP exchange.  It  is  only  used  in  Access-Reject
      packets.

   A  summary of the MS-CHAP-Error Attribute format is given below.  The
   fields are transmitted left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vendor-Type | Vendor-Length |     Ident     |    String...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+



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   Vendor-Type
      2 for MS-CHAP-Error.

   Vendor-Length
      > 3

   Ident
      The Ident field is one octet and aids  in  matching  requests  and
      replies.

   String
      This  field  contains up to 48 octets of specially formatted ASCII
      text, which is interpreted by the authenticating peer.  The format
      of this field is as follows:

         "E=eeeeeeeeee R=r C=cccccccccccccccc V=vvvvvvvvvv"

      where  the  "eeeeeeeeee"  represents  an ASCII representation of a
      decimal error code of up to 10 digits corresponding to one of  the
      following:

         646 ERROR_RESTRICTED_LOGON_HOURS
         647 ERROR_ACCT_DISABLED
         648 ERROR_PASSWD_EXPIRED
         649 ERROR_NO_DIALIN_PERMISSION
         691 ERROR_AUTHENTICATION_FAILURE
         709 ERROR_CHANGING_PASSWORD

      Implementations  should  deal  with  codes not on this list grace-
      fully, however.  Please note that (unlike PPP CHAP),  the  receipt
      of    some    of   these   error   codes   (in   particular,   the
      ERROR_PASSWD_EXPIRED code) will modify the subsequent operation of
      the  MS-CHAP  protocol.   The 'r' is a retry flag (set to '1' if a
      retry is allowed and '0' otherwise), the "cccccccccccccccc" repre-
      sents  16  hexadecimal digits ('0'-'F') specifying a new challenge
      value, and the "vvvvvvvvvv" is a decimal version  code  signifying
      the version of MS-CHAP supported by the server.


5.5.  MS-CHAP-CPW-1

   Description

      This  Attribute allows the user to change their password if it has
      expired.  This Attribute is only used in  Access-Request  packets,
      and  should  only  be  included  if an MS-CHAP-Error attribute was
      included in the immediately preceding  Access-Reject  packet,  the
      String  field  of  the  MS-CHAP-Error attribute indicated that the



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      user password had expired, and the MS-CHAP version is less than 2.

   A summary of the MS-CHAP-CPW-1  Attribute format is shown below.  The
   fields are transmitted from left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vendor-Type | Vendor-Length |     Code      |     Ident     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       LM-Old-Password
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        LM-Old-Password (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        LM-Old-Password (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        LM-Old-Password (cont)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       LM-New-Password
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        LM-New-Password (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        LM-New-Password (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        LM-New-Password (cont)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       NT-Old-Password
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        NT-Old-Password (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        NT-Old-Password (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        NT-Old-Password (cont)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       NT-New-Password
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        NT-New-Password (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        NT-New-Password (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                        NT-New-Password (cont)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |    New-LM-Password-Length   |             Flags             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Vendor-Type
      3 for MS-CHAP-PW-1




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   Vendor-Length
      72

   Code
      The Code field is one octet in length.  Its value is always 5.

   Ident
      The Ident field is one octet and aids  in  matching  requests  and
      replies.

   LM-Old-Password
      The LM-Old-Password field is 16 octets in length.  It contains the
      encrypted Lan Manager hash of the old password.

   LM-New-Password
      The LM-New-Password field is 16 octets in length.  It contains the
      encrypted Lan Manager hash of the new password.

   NT-Old-Password
      The NT-Old-Password field is 16 octets in length.  It contains the
      encrypted Lan Manager hash of the old password.

   NT-New-Password
      The NT-New-Password field is 16 octets in length.  It contains the
      encrypted Lan Manager hash of the new password.

   New-LM-Password-Length
      The  New-LM-Password-Length field is two octets in length and con-
      tains the length in octets of the new LAN Manager-compatible pass-
      word.

   Flags
      The Flags field is two octets in length.  If the least significant
      bit of the Flags field is one, this  indicates  that  the  NT-New-
      Password  and NT-Old-Password fields are valid and SHOULD be used.
      Otherwise, the LM-New-Password and LM-Old-Password fields MUST  be
      used.


5.6.  MS-CHAP-CPW-2

   Description

      This  Attribute allows the user to change their password if it has
      expired.  This Attribute is only used in  Access-Request  packets,
      and  should  only  be  included  if an MS-CHAP-Error attribute was
      included in the immediately preceding  Access-Reject  packet,  the
      String  field  of  the  MS-CHAP-Error attribute indicated that the



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      user password had  expired,  and  the  MS-CHAP  version  is  2  or
      greater.

   A summary of the MS-CHAP-CPW-2  Attribute format is shown below.  The
   fields are transmitted from left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vendor-Type | Vendor-Length |     Code      |     Ident     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Old-NT-Hash
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         Old-NT-Hash (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         Old-NT-Hash (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                         Old-NT-Hash (cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        Old-LM-Hash
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          Old-LM-Hash(cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          Old-LM-Hash(cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          Old-LM-Hash(cont)                      |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                        LM-Response
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          LM-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          LM-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          LM-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          LM-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          LM-Response (cont)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                         NT-Response
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          NT-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          NT-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          NT-Response (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          NT-Response (cont)



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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                          NT-Response (cont)                     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Flags             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Vendor-Type
      4 for MS-CHAP-PW-2

   Vendor-Length
      86

   Code
      6

   Ident
      The Ident field is one octet and aids  in  matching  requests  and
      replies.  The value of this field MUST be identical to that in the
      Ident field in all instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT-
      Enc-PW  and  MS-CHAP-PW-2 attributes contained in a single Access-
      Request packet.

   Old-NT-Hash
      The Old-NT-Hash field is 16 octets in length.  It contains the old
      Windows  NT  password hash encrypted with the new Windows NT pass-
      word hash.

   Old-LM-Hash
      The Old-LM-Hash field is 16 octets in length.  It contains the old
      Lan  Manager password hash encrypted with the new Windows NT pass-
      word hash.

   LM-Response
      The LM-Response field is 24 octets in length and holds an  encoded
      function  of  the  password  and  the received challenge.  If this
      field is empty, it SHOULD be zero-filled.

   NT-Response
      The NT-Response field is 24 octets in length and holds an  encoded
      function  of  the  password  and  the received challenge.  If this
      field is empty, it SHOULD be zero-filled.

   Flags
      The Flags field is two octets in length.  If the least significant
      bit  (bit  0) of this field is one, the NT-Response field is to be
      used in preference to the LM-Response  field  for  authentication.
      The  LM-Response field MAY still be used (if present), but the NT-
      Response SHOULD be tried first.  If least significant bit  of  the



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      field  is  zero, the NT-Response field MUST be ignored and the LM-
      Response field used instead.  If bit 1 of the Flags field is  one,
      the Old-LM-Hash field is valid and SHOULD be used.  If this bit is
      set, at least one instance of the MS-CHAP-LM-Enc-PW attribute MUST
      be included in the packet.


5.7.  MS-CHAP-LM-Enc-PW

   Description

      This Attribute contains the new Windows NT password encrypted with
      the old LAN Manager password hash.  The encrypted Windows NT pass-
      word  is 516 octets in length; since this is longer than the maxi-
      mum lengtth of a RADIUS attribute, the password must be split into
      several  attibutes for transmission.  A 2 octet sequence number is
      included in the attribute to help preserve ordering of  the  pass-
      word fragments.

      This Attribute is only used in Access-Request packets, in conjunc-
      tion with the MS-CHAP-CPW-2 attribute.  It should only be included
      if an MS-CHAP-Error attribute was included in the immediately pre-
      ceding Access-Reject packet, the String field of the MS-CHAP-Error
      attribute  indicated  that  the user password had expired, and the
      MS-CHAP version is 2 or greater.

   A summary of the MS-CHAP-LM-Enc-PW Attribute format is  shown  below.
   The fields are transmitted from left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vendor-Type | Vendor-Length |      Code     |     Ident     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |     Sequence-Number         |          String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Vendor-Type
      5 for MS-CHAP-LM-Enc-PW

   Vendor-Length
      > 6

   Code
      6.  Code is the same as for the MS-CHAP-PW-2 attribute.

   Ident
      The  Ident  field  is  one octet and aids in matching requests and



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      replies.  The value  of  this  field  MUST  be  identical  in  all
      instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT-Enc-PW and MS-CHAP-
      PW-2 attributes which  are  present  in  the  same  Access-Request
      packet.

   Sequence-Number
      The  Sequence-Number  field  is two octets in length and indicates
      which "chunk" of the encrypted password is contained in  the  fol-
      lowing String field.

   String
      The String field contains a portion of the encrypted password.


5.8.  MS-CHAP-NT-Enc-PW

   Description

      This Attribute contains the new Windows NT password encrypted with
      the old Windows NT password hash.  The encrypted Windows NT  pass-
      word  is 516 octets in length; since this is longer than the maxi-
      mum lengtth of a RADIUS attribute, the password must be split into
      several  attibutes for transmission.  A 2 octet sequence number is
      included in the attribute to help preserve ordering of  the  pass-
      word fragments.

      This Attribute is only used in Access-Request packets, in conjunc-
      tion with the MS-CHAP-CPW-2 attribute.  It should only be included
      if an MS-CHAP-Error attribute was included in the immediately pre-
      ceding Access-Reject packet, the String field of the MS-CHAP-Error
      attribute  indicated  that  the user password had expired, and the
      MS-CHAP version is 2 or greater.

   A summary of the MS-CHAP-NT-Enc-PW Attribute format is  shown  below.
   The fields are transmitted from left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vendor-Type | Vendor-Length |      Code     |     Ident     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |       Sequence-Number       |           String ...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Vendor-Type
      6 for MS-CHAP-NT-Enc-PW

   Vendor-Length



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      > 6

   Code
      6.  Code is the same as for the MS-CHAP-PW-2 attribute.

   Ident
      The  Ident  field  is  one octet and aids in matching requests and
      replies.  The value  of  this  field  MUST  be  identical  in  all
      instances of the MS-CHAP-LM-Enc-PW, MS-CHAP-NT-Enc-PW and MS-CHAP-
      PW-2 attributes which  are  present  in  the  same  Access-Request
      packet.

   Sequence-Number
      The  Sequence-Number  field  is two octets in length and indicates
      which "chunk" of the encrypted password is contained in  the  fol-
      lowing String field.

   String
      The String field contains a portion of the encrypted password.


5.9.  MS-CHAP-MPPE-Keys

   Description

      The  MS-CHAP-MPPE-Keys Attribute contains two session keys for use
      by the Microsoft Point-to-Point Encryption Protocol (MPPE).   This
      Attribute  is  only  included in Access-Accept packets.  Note that
      the keys are generative session keys; no processing need  be  done
      by the RADIUS client before using the keys in the MPPE protocol.

   A  summary  of the MS-CHAP-MPPE-Keys Attribute format is given below.
   The fields are transmitted left to right.

   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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Vendor-Type | Vendor-Length |           Keys
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            Keys (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            Keys (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            Keys (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            Keys (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            Keys (cont)



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   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            Keys (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                            Keys (cont)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
             Keys (cont)         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Vendor-Type
      12 for MS-CHAP-MPPE-Keys.

   Vendor-Length
      34

   Keys
      The Keys field consists of two logical sub-fields: the LM-Key  and
      the  NT-Key.   The LM-Key is eight octets in length and is derived
      from the first eight bytes of the  hashed  LAN  Manager  password.
      The  NT-Key  sub-field  is sixteen octets in length and is derived
      from the first sixteen octets of the hashed Windows  NT  password.
      The  format of the plaintext Keys field is illustrated in the fol-
      lowing diagram:

      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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           LM-Key
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               LM-Key (cont)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                           NT-Key
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               NT-Key (cont)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               NT-Key (cont)
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                               NT-Key (cont)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Padding
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                              Padding (cont)                        |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      The Keys field MUST be encrypted by the RADIUS  server  using  the
      same  method  defined  for  the User-Password Attribute [3].  Note
      that the padding is required because the method  referenced  above
      requires  the  field  to  be encrypted to be a multiple of sixteen
      octets in length.



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INTERNET-DRAFT          MS-CHAP RADIUS Attributes           October 1997


6.  Table of Attributes

The following table provides a guide to which of  the  above  attributes
may be found in which kinds of packets, and in what quantity.

   Request Accept Reject Challenge Acct-Request #  Attribute
   0+      0      0      0+        0            11 MS-CHAP-Challenge
   0+      0      0      0         0             1 MS-CHAP-Response
   0       0+     0      0         0+           10 MS-CHAP-Domain
   0       0      0+     0         0             2 MS-CHAP-Error
   0+      0      0      0         0             3 MS-CHAP-CPW-1
   0+      0      0      0         0             4 MS-CHAP-CPW-2
   0+      0      0      0         0             5 MS-CHAP-LM-Enc-PW
   0+      0      0      0         0             6 MS-CHAP-NT-Enc-PW
   0       0+     0      0         0            12 MS-CHAP-MPPE-Keys

The following table defines the meaning of the above table entries.

   0     This attribute MUST NOT be present in packet.
   0+    Zero or more instances of this attribute MAY be present in packet.
   0-1   Zero or one instance of this attribute MAY be present in packet.


7.  Security Considerations

MS-CHAP,  like  PPP  CHAP,  is  susceptible to dictionary attacks.  User
passwords should be chosen with care, and be  of  sufficient  length  to
deter easy guessing.  Although the scheme used to protect the Keys field
of the MS-CHAP-MPPE-Keys Attribute is believed to be  relatively  secure
on  the  wire,  RADIUS proxies will decrypt and re-encrypt the field for
forwarding.  Therefore, the MS-CHAP-MPPE-Keys attribute  SHOULD  NOT  be
used on networks where untrusted RADIUS proxies reside.


8.  Acknowledgements

Thanks   to   Carl   Rigney   (cdr@livingston.com),   Narendra   Gidwani
(nareng@microsoft.com), Steve Cobb (stevec@microsoft.com),  Pat  Calhoun
(pcalhoun@usr.com),  Dave  Mitton  (dmitton@baynetworks.com),  Paul Funk
(paul@funk.com), Gurdeep Singh Pall (gurdeep@microsoft.com) and Don Rule
(donaldr@microsoft.com) for useful suggestions and editorial feedback.


9.  Expiration Date

This document expires May 21, 1998.





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INTERNET-DRAFT          MS-CHAP RADIUS Attributes           October 1997


10.  Chair's Address

The RADIUS Working Group can be contacted via the current chair:

   Carl Rigney
   Livingston Enterprises
   4464 Willow Road
   Pleasanton, California  94588

   Phone: +1 510 426 0770
   E-Mail: cdr@livingston.com


11.  Author's Address

Questions about this memo can also be directed to:

   Glen Zorn
   Microsoft Corporation
   One Microsoft Way
   Redmond, Washington 98052

   Phone: +1 425 703 1559
   FAX:   +1 425 936 7329
   EMail: glennz@microsoft.com


12.  References

[1]  Simpson,  W.,  "PPP  Challenge  Handshake  Authentication  Protocol
     (CHAP)", RFC 1994, August 1996

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

[3]  Rigney,  C.,  et.  al.,  "Remote  Access Dial In User Service", RFC
     2138, April 1997














Zorn                                                           [Page 16]


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