Formal verification of security protocol with B method

Security Protocols are fundamental building block of many important applications. These protocols are used to achieve various security requirements such as confidentially, authentication, integrity etc. of the applications. These protocols must be tested for their functional correctness before they are used. In many of the protocol errors have been detected, in spite of investing lot of time in their design. Modified Needham Schroeder Symmetric Key Protocol is a security protocol that incorporates an exchange of messages between two or more agents, for establishing a cryptographic key, and authenticating the identities of the agents. Authentication protocol has to be designed in such a way that makes it robust against replay attacks by any intruder. In this paper, use of formal methods for verification of correction of modified Needham-Schroeder Symmetric Key Protocol is demonstrated. B method has been used for developing specification of modified Needham-Schroeder Symmetric Key protocol and thereafter specifications are model checked using proB model checker. The specifications are free from deadlock and satisfy the behaviour or properties of the system expressed as invariants. It is verified that specifications leaves no spaces for the replay attack.