MS-CHAP
{{Short description|Authentication protocol to validate users}}
MS-CHAP is the Microsoft version of the Challenge-Handshake Authentication Protocol, (CHAP).
Versions
The protocol exists in two versions, MS-CHAPv1 (defined in {{IETF RFC|2433}}) and MS-CHAPv2 (defined in {{IETF RFC|2759}}). MS-CHAPv2 was introduced with pptp3-fix that was included in Windows NT 4.0 SP4 and was added to Windows 98 in the "Windows 98 Dial-Up Networking Security Upgrade Release"{{cite web|title=Windows 98 Dial-Up Networking Security Upgrade Release Notes (August 1998)|url=https://support.microsoft.com/en-us/kb/189771|website=Support|publisher=Microsoft|date=August 1998}} and Windows 95 in the "Dial Up Networking 1.3 Performance & Security Update for MS Windows 95" upgrade. Windows Vista dropped support for MS-CHAPv1.
Applications
MS-CHAP is used as one authentication option in Microsoft's implementation of the PPTP protocol for virtual private networks. It is also used as an authentication option with RADIUS{{Cite IETF |rfc=2548 |title=Microsoft Vendor-specific RADIUS Attributes}} servers which are used with IEEE 802.1X (e.g., WiFi security using the WPA-Enterprise protocol). It is further used as the main authentication option of the Protected Extensible Authentication Protocol (PEAP).
Features
Compared with CHAP,{{cite IETF |rfc=1994 |title=PPP Challenge Handshake Authentication Protocol (CHAP)}} MS-CHAP:{{Cite IETF |rfc=2433 |title=Microsoft PPP CHAP Extensions}}{{Cite IETF |rfc=2759 |title=Microsoft PPP CHAP Extensions, Version 2}} works by negotiating CHAP Algorithm 0x80 (0x81 for MS-CHAPv2) in LCP option 3, Authentication Protocol. It provides an authenticator-controlled password change mechanism. It provides an authenticator-controlled authentication retry mechanism and defines failure codes returned in the Failure packet message field.
MS-CHAPv2 provides mutual authentication between peers by piggybacking a peer challenge on the response packet and an authenticator response on the success packet.
MS-CHAP requires each peer to either know the plaintext password, or an MD4 hash of the password, and does not transmit the password over the link. As such, it is not compatible with most password storage formats.
Flaws
Weaknesses have been identified in MS-CHAP and MS-CHAPv2.{{Cite web |url=http://www.schneier.com/paper-pptpv2.pdf |title=Cryptanalysis of Microsoft's PPTP Authentication Extensions (MS-CHAPv2) |first1=Bruce |last1=Schneier |authorlink1=Bruce Schneier |author2=Mudge |first3=David |last3=Wagner |website=schneier.com |date=19 October 1999 }} The DES encryption used in NTLMv1 and MS-CHAPv2 to encrypt the NTLM password hash enable custom hardware attacks utilizing the method of brute force.{{Cite web |url=http://penguin-breeder.org/pptp/download/pptp_mschapv2.pdf |title=Exploiting known security holes in Microsoft's PPTP Authentication Extensions (MS-CHAPv2) |first=Jochen |last=Eisinger |date=23 July 2001 |website=penguin-breeder.org}}
As of 2012, MS-CHAP had been completely broken. The divide-and-conquer attack only requires breaking a single DES key, which is not difficult with modern GPUs and FPGAs.{{cite web|url=https://www.cloudcracker.com/blog/2012/07/29/cracking-ms-chap-v2/|title=Divide and Conquer: Cracking MS-CHAPv2 with a 100% success rate|year=2012|publisher=David Hulton|archive-url=https://web.archive.org/web/20160316174007/https://www.cloudcracker.com/blog/2012/07/29/cracking-ms-chap-v2/|archive-date=16 March 2016|access-date=2013-03-10}} MS-CHAP as a whole can be viewed as a smoke-and-mirrors protocol, in that ~80% of the protocol provides no real security; it just makes the construction very complicated and thus appear infeasible to crack. In reality, this ~80% is either plaintext messages, or messages easily derived from those sent in plaintext. The actual security core is reduced to the NTLM password hash and DES encryptions keyed by the hash output, which is fundamentally weak.
After Windows 11 22H2, with the default activation of Windows Defender Credential Guard, users can no longer authenticate with MSCHAPv2. The developers recommend a move from MSCHAPv2-based connections to certificate-based authentication (such as PEAP-TLS or EAP-TLS).{{Cite web|url=https://learn.microsoft.com/en-us/windows/security/identity-protection/credential-guard/credential-guard-considerations|title=Considerations when using Windows Defender Credential Guard - Windows Security|date=January 27, 2023|website=learn.microsoft.com}}
See also
References
{{Reflist|30em}}
{{Authentication APIs}}
Category:Broken cryptography algorithms