R-STELLAR: A Resilient Synthesizable Signature Attenuation SCA Protection on AES-256 With Built-In Attack-on-Countermeasure Detection

Abstract

Side-channel attacks (SCAs) remain a significant threat to the security of cryptographic systems in modern embedded devices. Even mathematically secure cryptographic algorithms, when implemented in hardware, inadvertently leak information through physical side-channel signatures, such as power consumption, electromagnetic (EM) radiation, light emissions, and acoustic emanations. Exploiting these side channels significantly reduces the attacker’s search space. In recent years, physical countermeasures have significantly increased the minimum traces-to-disclosure (MTD) to 1 billion. Among them, signature attenuation is the first method to achieve this mark. Signature attenuation often relies on analog techniques, and digital signature attenuation reduces MTD to 20 million, requiring additional methods for high resilience. We focus on improving the digital signature attenuation by an order of magnitude (MTD 200M). Additionally, we explore possible attacks against signature attenuation countermeasure. We introduce a voltage-drop linear-region biasing (VLB) attack technique that reduces the MTD to over 2000 times less than the previous threshold. This is the first known attack against a physical SCA countermeasure. We have implemented an attack detector with a response time of 0.8 ms to detect such attacks, limiting the SCA leakage window to sub-ms, which is insufficient for a successful attack.