MS-CHAP

MS-CHAP is Microsoft's adaptation of Challenge-Handshake Authentication Protocol (CHAP). The current version is MS-CHAP v2. MS-CHAP requires both client and server to authenticate to each other. This is in distinction to CHAP, which only requires the client to authenticate to the server.

See: RFC 2759.

References:

http://technet.microsoft.com/en-us/library/cc957983.aspx

http://www.schneier.com/paper-pptpv2.html