Research of authentication mechanism in CHAP

The method of double-factor authentication is usually embedded in CHAP (Challenge Handshake Authentication Protocol) to enhance the security of the authentication service. The CHAP protocol with double-factor authentication is formally verified from the intruder's aspect, and some data structures is abstracted from the protocol to build up the framework of reasoning-logic. By the means of adverse deduction, the framework of reasoning-logic is analyzed thoroughly, the flaws of the CHAP protocol is found and the corresponding attacking scenario is given. The result shows that the CHAP protocol with double-factor authentication has some security holes and can't achieve the security requirement of the design.