Formal analysis of PIN block attacks

Personal identification number (PIN) blocks are 64-bit strings that encode a PIN ready for encryption and secure transmission in banking networks. These networks employ tamper-proof hardware security modules (HSMs) to perform sensitive cryptographic operations, such as checking the correctness of a PIN typed by a customer. The use of these HSMs is controlled by an API designed to enforce security. PIN block attacks are unanticipated sequences of API commands which allow an attacker to determine the value of a PIN in an encrypted PIN block. This paper describes a framework for formal analysis of such attacks. Our analysis is probabilistic, and is automated using constraint logic programming and probabilistic model checking.