Microsoft PPP CHAP Extensions, Version 2
RFC 2759

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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].

Zorn                         Informational                      [Page 1]
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

Zorn                         Informational                      [Page 2]
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