rfc2548.txt

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Network Working Group                                            G. Zorn
Request for Comments: 2548                         Microsoft Corporation
Category: Informational                                       March 1999


              Microsoft Vendor-specific RADIUS Attributes

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 (1999).  All Rights Reserved.

Abstract

   This document describes the set of Microsoft vendor-specific RADIUS
   attributes.  These attributes are designed to support Microsoft
   proprietary dial-up protocols and/or provide support for features
   which is not provided by the standard RADIUS attribute set [3].  It
   is expected that this memo will be updated whenever Microsoft defines
   a new vendor-specific attribute, since its primary purpose is to
   provide an open, easily accessible reference for third-parties
   wishing to interoperate with Microsoft products.

1.  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].

2.  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-Specific 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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RFC 2548      Microsoft Vendor-specific RADIUS Attributes     March 1999


2.1.  Attributes for Support of MS-CHAP Version 1

2.1.1.  Introduction

   Microsoft created Microsoft Challenge-Handshake Authentication
   Protocol (MS-CHAP) [4] to authenticate remote Windows workstations,
   providing the functionality to which LAN-based users are accustomed.
   Where possible, MS-CHAP is consistent with standard CHAP [5], 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 section reflect these differences.

2.1.2.  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.










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RFC 2548      Microsoft Vendor-specific RADIUS Attributes     March 1999


    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.

2.1.3.  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.

























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RFC 2548      Microsoft Vendor-specific RADIUS Attributes     March 1999


    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)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                             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.





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RFC 2548      Microsoft Vendor-specific RADIUS Attributes     March 1999


   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.

2.1.4.  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.










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RFC 2548      Microsoft Vendor-specific RADIUS Attributes     March 1999


2.1.5.  MS-CHAP-Error

   Description

      The MS-CHAP-Error Attribute contains error data related to the
      preceding MS-CHAP exchange.  This Attribute may be used in both
      MS-CHAP-V1 and MS-CHAP-V2 (see below) exchanges.  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...
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   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 specially formatted ASCII text, which is
      interpreted by the authenticating peer.

2.1.6.  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 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.






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RFC 2548      Microsoft Vendor-specific RADIUS Attributes     March 1999


    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)
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+