Microsoft PPP CHAP Extensions (RFC2433)
Original Publication Date: 1998-Oct-01
Included in the Prior Art Database: 2019-Feb-11
Internet Society Requests For Comment (RFCs)
G. Zorn: AUTHOR [+1]
The Point-to-Point Protocol (PPP) 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 memo provides information for the Internet community.
Network Working Group G. Zorn Request for Comments: 2433 S. Cobb Category: Informational Microsoft Corporation October 1998
Microsoft PPP CHAP Extensions
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 (C) The Internet Society (1998). All Rights Reserved.
The protocol described here has significant vulnerabilities. People planning on implementing or using this protocol should read section 12, "Security Considerations".
The Point-to-Point Protocol (PPP)  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 Microsoft’s PPP CHAP dialect (MS-CHAP), which extends the user authentication functionality provided on Windows networks to remote workstations. MS-CHAP is closely derived from the PPP Challenge Handshake Authentication Protocol described in RFC 1994 , which the reader should have at hand.
The algorithms used in the generation of various MS-CHAP protocol fields are described in an appendix.
Microsoft created MS-CHAP to authenticate remote Windows workstations, providing the functionality to which LAN-based users are accustomed while integrating the encryption and hashing algorithms used on Windows networks.
Zorn & Cobb Informational [Page 1]
RFC 2433 Microsoft PPP CHAP Extensions Ocotober 1998
Where possible, MS-CHAP is consistent with standard CHAP. 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’s Windows NT 3.5, 3.51 and 4.0, and Windows95 networking products. The MS-CHAP format does not require the authenticator to store a clear-text or reversibly encrypted password.
* MS-CHAP provides authenticator-controlled authentication retry and password changing mechanisms.
* MS-CHAP defines a set of reason-for-failure codes returned in the Failure packet Message field.
3. 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 .
4. LCP Configuration
The LCP configuration for MS-CHAP is identical to that for standard CHAP, except that the Algorithm field has value 0x80, rather than the MD5 value 0x05. PPP implementations which do not support MS-CHAP, but correctly implement LCP Config-Rej, should have no problem dealing with this non-standard option.
5. Challenge Packet
The MS-CHAP Challenge packet is identical in format to the standard CHAP Challenge packet.
MS-CHAP authenticators send an 8-octet challeng...