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 is a large number of authentication protocols that prove to be insecure. Wulf et al. have proposed in [1] a protocol by which an entity can authenticate in a distributed system environment without using any shared secret. This paper will make a brief analysis of the proposed protocol and will show 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.