Cryptanalysis of an authentication protocol

Authentication protocols have applications in many fields. The security of authentication protocols is commonly based on cryptographic primitives. Constructing secure authentication protocols is not an easy challenge and there are a large number of authentication protocols that prove to be insecure. Wulf et al. have proposed a protocol by which an entity can authenticate in a distributed system environment without using any shared secret. This paper makes a brief analysis of the proposed protocol and shows how it can be broken. The protocol will be broken by using multiplicative inverses of the integers from Z_n, where n is a prime number.