Low Cost Built in Self Test for Public Key Crypto Cores

The testability of cryptographic cores brings an extra dimension to the process of digital circuits testing security. The benefits of the classical methods such as the scan-chain method introduce new vulnerabilities concerning the data protection. The Built-In Self-Test (BIST) is considered to be the most suitable countermeasure for this purpose. In this work we propose the use of a digit-serial multiplier over GF (2m), that is at the heart of many public-key cryptosystems, as a basic building block for the BIST circuitry. We show how the multiplier can be configuredto operate as a Test Pattern Generator and a Signature Analyzer. Furthermore, the multiplier becomes a fully self-testable design. All the additional features come at the cost of only a few extra gates. With a hardware overhead of 0.33 % this approach makes the multiplier perfectly suitable for low-end embedded devices.