July 29, 2012 — IDG News Service — Security researchers released two tools at the Defcon security conference that can be used to crack the encryption of any PPTP (Point-to-Point Tunneling Protocol) and WPA2-Enterprise (Wireless Protected Access) sessions that use MS-CHAPv2 for authentication.
MS-CHAPv2 is an authentication protocol created by Microsoft and introduced in Windows NT 4.0 SP4. Despite its age, it is still used as the primary authentication mechanism by most PPTP virtual private network (VPN) clients.
MS-CHAPv2 has been known to be vulnerable to dictionary-based brute force attacks since 1999, when a cryptanalysis of the protocol was published by cryptographer Bruce Schneier and other researchers.
However, the common belief on the Internet is that if you have a strong password then it's ok, said Moxie Marlinspike, the security researcher who developed ChapCrack, one of the tools released at Defcon. "What we demonstrated is that it doesn't matter. There's nothing you can do."
ChapCrack can take captured network traffic that contains a MS-CHAPv2 network handshake (PPTP VPN or WPA2 Enterprise handshake) and reduce the handshake's security to a single DES (Data Encryption Standard) key.
This DES key can then be submitted to CloudCracker.com -- a commercial online password cracking service that runs on a special FPGA cracking box developed by David Hulton of Pico Computing -- where it will be decrypted in under a day.
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