An attack on the Interlock Protocol when used for authentication

Exponential key exchange may be used to establish secure communications between two parties who do not share a private key. It fails in the presence of an active wiretap, however. Davies and Price suggest the use of Shamir and Rivest´s “Interlock Protocol” to surmount this difficulty. The authors demonstrate that an active attacker can, at the cost of a timeout alarm, bypass the passwork exchange, and capture the passwords used. Furthermore, if the attack is from a terminal or workstation attempting to contact a computer, the attacker will have access before any alarm can be sounded