Security of Countermeasures Against State-of-the-Art Differential Scan Attacks

Test compression schemes have been claimed to provide a certain level of security against scan-based side-channel attacks. To mitigate these attacks, a number of scan attack countermeasures are proposed in the literature. Recently, a new differential scan attack (DSA) is proposed which focuses on the S-box outputs rather than the S-box inputs as in previous attacks. In this paper, a systematic security analysis of the most popular scan attack countermeasures against this differential scan attack is given. The countermeasures are evaluated when they are used together with industrial test compression schemes on a straightforward AES design. Security of the countermeasures is evaluated by emulating their behaviour in software, and the gain in security is experimentally investigated. Our experiments show that when the new DSA (focusing on the S-box output) is considered, both scan chain scrambling and partial scan countermeasures fail to provide sufficient security.