rfc2759.txt

radius服务器

Network Working Group                                            G. Zorn
Request for Comments: 2759                         Microsoft Corporation
Category: Informational                                     January 2000


                Microsoft PPP CHAP Extensions, Version 2


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 (2000).  All Rights Reserved.

Abstract

   The Point-to-Point Protocol (PPP) [1] provides a standard method for
   transporting multi-protocol datagrams over point-to-point links.  PPP
   defines an extensible Link Control Protocol and a family of Network
   Control Protocols (NCPs) for establishing and configuring different
   network-layer protocols.

   This document describes version two of Microsoft's PPP CHAP dialect
   (MS-CHAP-V2).  MS-CHAP-V2 is similar to, but incompatible with, MS-
   CHAP version one (MS-CHAP-V1, described in [9]).  In particular,
   certain protocol fields have been deleted or reused but with
   different semantics.  In addition, MS-CHAP-V2 features mutual
   authentication.

   The algorithms used in the generation of various MS-CHAP-V2 protocol
   fields are described in section 8.  Negotiation and hash generation
   examples are provided in section 9.

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 [3].









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RFC 2759                  Microsoft MS-CHAP-V2              January 2000


Table of Contents

   1. Introduction  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2. LCP Configuration . . . . . . . . . . . . . . . . . . . . . . .  3
   3. Challenge Packet  . . . . . . . . . . . . . . . . . . . . . . .  3
   4. Response Packet . . . . . . . . . . . . . . . . . . . . . . . .  4
   5. Success Packet  . . . . . . . . . . . . . . . . . . . . . . . .  4
   6. Failure Packet  . . . . . . . . . . . . . . . . . . . . . . . .  5
   7. Change-Password Packet  . . . . . . . . . . . . . . . . . . . .  6
   8. Pseudocode  . . . . . . . . . . . . . . . . . . . . . . . . . .  7
   8.1. GenerateNTResponse()  . . . . . . . . . . . . . . . . . . . .  7
   8.2. ChallengeHash() . . . . . . . . . . . . . . . . . . . . . . .  8
   8.3. NtPasswordHash()  . . . . . . . . . . . . . . . . . . . . . .  9
   8.4. HashNtPasswordHash()  . . . . . . . . . . . . . . . . . . . .  9
   8.5. ChallengeResponse() . . . . . . . . . . . . . . . . . . . . .  9
   8.6. DesEncrypt()  . . . . . . . . . . . . . . . . . . . . . . . . 10
   8.7. GenerateAuthenticatorResponse() . . . . . . . . . . . . . . . 10
   8.8. CheckAuthenticatorResponse()  . . . . . . . . . . . . . . . . 12
   8.9. NewPasswordEncryptedWithOldNtPasswordHash() . . . . . . . . . 12
   8.10. EncryptPwBlockWithPasswordHash() . . . . . . . . . . . . . . 13
   8.11. Rc4Encrypt() . . . . . . . . . . . . . . . . . . . . . . . . 13
   8.12. OldNtPasswordHashEncryptedWithNewNtPasswordHash()  . . . . . 14
   8.13. NtPasswordHashEncryptedWithBlock() . . . . . . . . . . . . . 14
   9. Examples  . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
   9.1. Negotiation Examples  . . . . . . . . . . . . . . . . . . . . 14
   9.1.1. Successful authentication . . . . . . . . . . . . . . . . . 15
   9.1.2. Authenticator authentication failure  . . . . . . . . . . . 15
   9.1.3. Failed authentication with no retry allowed . . . . . . . . 15
   9.1.4. Successful authentication after retry . . . . . . . . . . . 15
   9.1.5. Failed hack attack with 3 attempts allowed  . . . . . . . . 15
   9.1.6. Successful authentication with password change  . . . . . . 16
   9.1.7. Successful authentication with retry and password change. . 16
   9.2. Hash Example  . . . . . . . . . . . . . . . . . . . . . . . . 16
   9.3. Example of DES Key Generation . . . . . . . . . . . . . . . . 17
   10. Security Considerations  . . . . . . . . . . . . . . . . . . . 17
   11. References . . . . . . . . . . . . . . . . . . . . . . . . . . 18
   12. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19
   13. Author's Address . . . . . . . . . . . . . . . . . . . . . . . 19
   14. Full Copyright Statement . . . . . . . . . . . . . . . . . . . 20












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RFC 2759                  Microsoft MS-CHAP-V2              January 2000


1.  Introduction

   Where possible, MS-CHAP-V2 is consistent with both MS-CHAP-V1 and
   standard CHAP.  Briefly, the differences between MS-CHAP-V2 and MS-
   CHAP-V1 are:

   *  MS-CHAP-V2 is enabled by negotiating CHAP Algorithm 0x81 in LCP
      option 3, Authentication Protocol.

   *  MS-CHAP-V2 provides mutual authentication between peers by
      piggybacking a peer challenge on the Response packet and an
      authenticator response on the Success packet.

   *  The calculation of the "Windows NT compatible challenge response"
      sub-field in the Response packet has been changed to include the
      peer challenge and the user name.

   *  In MS-CHAP-V1, the "LAN Manager compatible challenge response"
      sub-field was always sent in the Response packet.  This field has
      been replaced in MS-CHAP-V2 by the Peer-Challenge field.

   *  The format of the Message field in the Failure packet has been
      changed.

   *  The Change Password (version 1) and Change Password (version 2)
      packets are no longer supported. They have been replaced with a
      single Change-Password packet.

2.  LCP Configuration

   The LCP configuration for MS-CHAP-V2 is identical to that for
   standard CHAP, except that the Algorithm field has value 0x81, rather
   than the MD5 value 0x05.  PPP implementations which do not support
   MS-CHAP-V2, but correctly implement LCP Config-Rej, should have no
   problem dealing with this non-standard option.

3.  Challenge Packet

   The MS-CHAP-V2 Challenge packet is identical in format to the
   standard CHAP Challenge packet.

   MS-CHAP-V2 authenticators send an 16-octet challenge Value field.
   Peers need not duplicate Microsoft's algorithm for selecting the 16-
   octet value, but the standard guidelines on randomness [1,2,7] SHOULD
   be observed.

   Microsoft authenticators do not currently provide information in the
   Name field.  This may change in the future.



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RFC 2759                  Microsoft MS-CHAP-V2              January 2000


4.  Response Packet

   The MS-CHAP-V2 Response packet is identical in format to the standard
   CHAP Response packet.  However, the Value field is sub-formatted
   differently as follows:

   16 octets: Peer-Challenge
    8 octets: Reserved, must be zero
   24 octets: NT-Response
    1 octet : Flags

   The Peer-Challenge field is a 16-octet random number.  As the name
   implies, it is generated by the peer and is used in the calculation
   of the NT-Response field, below.  Peers need not duplicate
   Microsoft's algorithm for selecting the 16-octet value, but the
   standard guidelines on randomness [1,2,7] SHOULD be observed.

   The NT-Response field is an encoded function of the password, the
   user name, the contents of the Peer-Challenge field and the received
   challenge as output by the routine GenerateNTResponse() (see section
   8.1, below).  The Windows NT password is a string of 0 to
   (theoretically) 256 case-sensitive Unicode [8] characters.  Current
   versions of Windows NT limit passwords to 14 characters, mainly for
   compatibility reasons; this may change in the future.  When computing
   the NT-Response field contents, only the user name is used, without
   any associated Windows NT domain name.  This is true regardless of
   whether a Windows NT domain name is present in the Name field (see
   below).

   The Flag field is reserved for future use and MUST be zero.

   The Name field is a string of 0 to (theoretically) 256 case-sensitive
   ASCII characters which identifies the peer's user account name.  The
   Windows NT domain name may prefix the user's account name (e.g.
   "BIGCO\johndoe" where "BIGCO" is a Windows NT domain containing the
   user account "johndoe").  If a domain is not provided, the backslash
   should also be omitted, (e.g. "johndoe").

5.  Success Packet

   The Success packet is identical in format to the standard CHAP
   Success packet.  However, the Message field contains a 42-octet
   authenticator response string and a printable message.  The format of
   the message field is illustrated below.

   "S=<auth_string> M=<message>"





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RFC 2759                  Microsoft MS-CHAP-V2              January 2000


   The <auth_string> quantity is a 20 octet number encoded in ASCII as
   40 hexadecimal digits.  The hexadecimal digits A-F (if present) MUST
   be uppercase.  This number is derived from the challenge from the
   Challenge packet, the Peer-Challenge and NT-Response fields from the
   Response packet, and the peer password as output by the routine
   GenerateAuthenticatorResponse() (see section 8.7, below).  The
   authenticating peer MUST verify the authenticator response when a
   Success packet is received.  The method for verifying the
   authenticator is described in section 8.8, below.  If the
   authenticator response is either missing or incorrect, the peer MUST
   end the session.

   The <message> quantity is human-readable text in the appropriate
   charset and language [12].

6.  Failure Packet

   The Failure packet is identical in format to the standard CHAP
   Failure packet.  There is, however, formatted text stored in the
   Message field which, contrary to the standard CHAP rules, does affect
   the operation of the protocol.  The Message field format is:

      "E=eeeeeeeeee R=r C=cccccccccccccccccccccccccccccccc V=vvvvvvvvvv
M=<msg>"

      where

      The "eeeeeeeeee" is the ASCII representation of a decimal error
      code (need not be 10 digits) corresponding to one of those listed
      below, though implementations should deal with codes not on this
      list gracefully.

         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

      The "r" is an ASCII flag set to '1' if a retry is allowed, and '0'
      if not.  When the authenticator sets this flag to '1' it disables
      short timeouts, expecting the peer to prompt the user for new
      credentials and resubmit the response.

      The "cccccccccccccccccccccccccccccccc" is the ASCII representation
      of a hexadecimal challenge value.  This field MUST be exactly 32
      octets long and MUST be present.




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RFC 2759                  Microsoft MS-CHAP-V2              January 2000


      The "vvvvvvvvvv" is the ASCII representation of a decimal version
      code (need not be 10 digits) indicating the password changing
      protocol version supported on the server.  For MS-CHAP-V2, this
      value SHOULD always be 3.

      <msg> is human-readable text in the appropriate charset and
      language [12].

7.  Change-Password Packet

   The Change-Password packet does not appear in either standard CHAP or
   MS-CHAP-V1.  It allows the peer to change the password on the account
   specified in the preceding Response packet.  The Change-Password
   packet should be sent only if the authenticator reports
   ERROR_PASSWD_EXPIRED (E=648) in the Message field of the Failure
   packet.

   This packet type is supported by recent versions of Windows NT 4.0,
   Windows 95 and Windows 98.  It is not supported by Windows NT 3.5,
   Windows NT 3.51, or early versions of Windows NT 4.0, Windows 95 and
   Windows 98.

   The format of this packet is as follows:

        1 octet  : Code
        1 octet  : Identifier
        2 octets : Length
      516 octets : Encrypted-Password
       16 octets : Encrypted-Hash
       16 octets : Peer-Challenge
        8 octets : Reserved
       24 octets : NT-Response
        2-octet  : Flags

   Code
      7

   Identifier
      The Identifier field is one octet and aids in matching requests
      and replies.  The value is the Identifier of the received Failure
      packet to which this packet responds plus 1.

   Length
      586







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RFC 2759                  Microsoft MS-CHAP-V2              January 2000


   Encrypted-Password
      This field contains the PWBLOCK form of the new Windows NT
      password encrypted with the old Windows NT password hash, as
      output by the NewPasswordEncryptedWithOldNtPasswordHash() routine
      (see section 8.9, below).

   Encrypted-Hash
      This field contains the old Windows NT password hash encrypted
      with the new Windows NT password hash, as output by the
      OldNtPasswordHashEncryptedWithNewNtPasswordHash() routine (see
      section 8.12, below).

   Peer-Challenge
      A 16-octet random quantity, as described in the Response packet
      description.

   Reserved
      8 octets, must be zero.

   NT-Response
      The NT-Response field (as described in the Response packet
      description), but calculated on the new password and the challenge
      received in the Failure packet.

   Flags
      This field is two octets in length.  It is a bit field of option
      flags where 0 is the least significant bit of the 16-bit quantity.
      The format of this field is illustrated in the following diagram:

                    1
          5 4 3 2 1 0 9 8 7 6 5 4 3 2 1 0
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
         |                               |