Tools released at Defcon by security researcher Moxie Marlinspike can crack widely used PPTP encryption in under a day using CloudCracker. Moxie Marlinspike and few other researchers developed software 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.
Before we go any further let’s go deeper into these protocols.
The Point-to-Point Tunneling Protocol (PPTP) is a method for implementing virtual private networks. PPTP uses a control channel over TCP and a GRE tunnel operating to encapsulate PPP packets. The PPTP specification does not describe encryption or authentication features and relies on the Point-to-Point Protocol being tunneled to implement security functionality. PPTP implementation is widely used in Microsoft Windows products, and implements various levels of authentication and encryption natively as standard features of the Windows PPTP stack. The intended use of this protocol is to provide similar levels of security and remote access as typical VPN products.
Wi-Fi Protected Access II (WPA2) is a security protocol and security certification programs developed by the Wi-Fi Alliance to secure wireless computer networks. WPA2 became available in 2004 and is common shorthand for the full IEEE 802.11i or IEEE 802.11i-2004 standard. WPA2 has two encryption methods one called Advanced Encryption Standard (AES) and one called Temporal Key Integrity Protocol (TKIP) both of these allow for stronger encryption. The WPA2 protocol creates a new encryption key for each session. As part of WPA2 Pairwise Master Key caching, where faster connections occur when a client goes back to a wireless access point to which the client already is authenticated. Pre-Shared Key or PSK supports two different authentication mechanisms one using standard RADIUS servers and the other with a shared key, similar to how WEP works.
MS-CHAP2 is the Microsoft version of the Challenge-Handshake Authentication Protocol, CHAP. MS-CHAP is used as one authentication option in Microsoft’s implementation of the PPTP protocol for virtual private networks. MS-CHAP2 used as an authentication option with RADIUS servers which are used for WiFi security using the WPA-Enterprise protocol. It is further used as the main authentication option of the Protected Extensible Authentication Protocol (PEAP). MS-CHAP v2 provides two-way authentication and multiple cryptographic keys to secure transmitted and received data.
Marlinspike’s advice to businesses and VPN providers was to stop using PPTP and switch to other technologies like IPsec or OpenVPN. Companies with wireless network deployments that use WPA2 Enterprise security with MS-CHAPv2 authentication should also switch to an alternative.
This is the video of Marlinspike’s presentation.