Improved SPI Calculus for Reasoning on Cryptographic Protocols

Most of cryptographic protocols are subjects to very subtle attacks. Therefore, many researchers have developed tools to model and analyze protocols to guarantee their security properties. The spi calculus has proved to be useful for analyzing and reasoning on cryptographic protocols. However, current works assumed that the spi calculus dealt with transferring a single unstructured message for sending each message in a single action, which is mostly needed in implementing real protocols with an open environment, such case cause a problem in proving the freshness of generated keys for each output action. In this paper, we introduced an improved version of spi calculus called the Tspi calculus that provides the ability for solving the problem of tuple of messages using nested partial map function and guarantee the freshness of generated keys by the use of an evolution function for each action in the running processes for making suitable decision during interaction with an open environment such as e-commerce protocols. Index Term-Cryptographic protocol, Cryptographic protocol analysis, spi calculus, partial map function, evaluation function, testing equivalence.