In light of last month’s announcement by Moxie Marlinspike and David Hulton that they developed a method for decrypting Windows VPN traffic in under 24 hours, it is now important to stop using MS-CHAPv2 as a means of authenticating VPN passwords.
There is a relatively simple fix for this. Microsoft VPN servers have the ability to authenticate passwords using another protocol called PEAP, also known as PEAP-EAP-MSCHAPv2. The only reason one might avoid using PEAP in the first place is that the Microsoft documentation is confusing and describes a requirement for Public Key Infrastructure (PKI) deployment. The PKI as described in Deploying Remote Access VPNs requires anywhere from one to three servers just to issue certificates. However, it only specifies the PKI requirement for a slightly different protocol called EAP-TLS.
To be clear, PEAP does not require a full-blown PKI or even an internal Certificate Authority. You can, in fact, use the same certificate that has been, or would be, issued to a web server for SSL encryption. There is no reason to add a second certificate just for a VPN server. This also means there is no investment required in PKI if a free certificate issuer is used, such as startssl.com.
Below is a brief tutorial for configuring an existing RRAS installation with PEAP-MS-CHAPv2.
Ruled (lined paper)
