Deriving MPPE Keys From MS-CHAP V1 Credentials

Document Type Expired Internet-Draft (pppext WG)
Author Glen Zorn 
Last updated 1998-09-22
Stream Internet Engineering Task Force (IETF)
Intended RFC status (None)
Expired & archived
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Stream WG state WG Document
Document shepherd No shepherd assigned
IESG IESG state Expired
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This Internet-Draft is no longer active. A copy of the expired Internet-Draft can be found at


The Point-to-Point Protocol (PPP) [1] provides a standard method for transporting multi-protocol datagrams over point-to-point links. The PPP Compression Control Protocol [2] provides a method to negotiate and utilize compression protocols over PPP encapsulated links. The Microsoft Challenge-Handshake Authentication Protocol (MS-CHAP) [3] is a Microsoft-proprietary PPP authentication protocol, providing the functionality to which LAN-based users are accustomed while integrating the encryption and hashing algorithms used on Windows networks. Microsoft Point to Point Encryption (MPPE) [4] is a means of represent- ing PPP packets in an encrypted form. MPPE uses the RSA RC4 [5] algorithm to provide data confidentiality. The length of the session key to be used for initializing encryption tables can be negotiated. MPPE currently supports 40-bit and 128-bit session keys. MPPE session keys are changed frequently; the exact frequency depends upon the options negotiated, but may be every packet. MPPE is negotiated within option 18 [6] in the Compression Control Protocol. This document describes the method used to derive the initial MPPE ses- sion keys from MS-CHAP credentials. The algorithm used to change ses- sion keys during a session is described in [4].


Glen Zorn (

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