A BIST-based Dynamic Obfuscation Scheme for Resilience against Removal and Oracle-guided Attacks*

BISTLock is a recently proposed logic-locking technique that integrates a barrier finite-state-machine (FSM) with the built-in self-test (BIST) controller. We demonstrate the vulnerability of BISTLock to removal/bypass attacks and develop countermeasures to make it resilient against not only removal attacks but any form of Oracle-guided attack. Removal resilience is achieved through the incorporation of an input-signal scrambler. We demonstrate the vulnerability of the standalone scrambler to the SAT attack and present a reconfigurable LFSR-based dynamic authenticator that achieves SAT resilience. The proposed solution provides dynamic obfuscation upon the application of an incorrect key and prevents Oracle access to the attacker. We also present a security analysis of the overall system against Oraclefree attacks such as BMC-based sequential SAT and the FSM reverse engineering attack. We evaluate the security strength of the proposed solution and show that hardware overhead is low for a broad set of benchmark circuits.