Authentication protocol to validate users
MS-CHAP
is the
Microsoft
version of the
Challenge-Handshake Authentication Protocol
, (CHAP).
Versions
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The protocol exists in two versions, MS-CHAPv1 (defined in
RFC
2433
) and MS-CHAPv2 (defined in
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"
[1]
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
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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
[2]
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
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Compared with CHAP,
[3]
MS-CHAP:
[4]
[5]
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
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Weaknesses have been identified in MS-CHAP and MS-CHAPv2.
[6]
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.
[7]
As of 2012, MS-CHAP had been completely broken.
[8]
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).
[9]
See also
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References
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