Microsoft PPP CHAP Extensions (RFC2433)
Original Publication Date: 1998-Oct-01
Included in the Prior Art Database: 2000-Sep-13
Internet Society Requests For Comment (RFCs)
G. Zorn: AUTHOR [+2]
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.
Network Working Group G. Zorn
Request for Comments: 2433 S. Cobb
Category: Informational Microsoft Corporation
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
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.
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
* 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 ...