On Evaluating the Security of Dynamic Scan Obfuscation Scheme

Scan design is the most commonly used technique to ensure high test coverage in contemporary chips. However, attackers may use it as a trapdoor to gain access to the chip internals. Thus, it affects the overall chip security. Several techniques have been proposed to protect sensitive data from hackers. Recently, a countermeasure has been proposed that obfuscates the scan data using a test key. This scheme looks simple and effective against all the existing scan-based attacks. However, a detailed analysis of the scheme reveals that it is vulnerable to scan-based side-channel attacks. In this paper, it is shown that the test key could be retrieved successfully, and hence the security provided by this scheme is rendered ineffective. To address this vulnerability, a countermeasure is also proposed.