Differential Scan Attack on AES with X-tolerant and X-masked Test Response Compactor

Scan-chains are test infrastructures included in a circuit for providing high fault coverage. However, they can be exploited by an attacker as a side-channel in the case of a cryptographic application like AES. Test Compression and thereafter X-tolerance and X-masking over it, which reduce test effort without compromising on testability, can help in counteracting scan-based attacks. This work focuses on the security issues of an AES-circuit containing test compression with X-masking and X-tolerance logic. With experimental results, we show the weakness of such an AES circuit against our modified differential scan-attack. Finally, the paper outlines two suitable countermeasures to prevent such attacks.