: Cryptographic protocols are used to achieve secure communication over insecure networks. Weaknesses in such protocols are hard to identify, as they can be the result of subtle design flaws. Formal verification techniques provide rigid and thorough means to evaluate security protocols. This paper demonstrates the process of formal verification by applying a logic to a security protocol intended for use in mobile communications. As a result of the verification, 8 failed protocol goals are identified. Further, a new attack on the protocol is outlined. The presence of weaknesses in published protocols highlights the importance of formal verification to prevent insecure protocols reaching the public domain.