Securing Cloud FPGAs Against Power Side-Channel Attacks: A Case Study on Iterative AES

The various benefits of multi-tenanting, such as higher device utilization and increased profit margin, intrigue the cloud field-programmable gate array (FPGA) servers to include multi-tenanting in their infrastructure. However, this property makes these servers vulnerable to power side-channel (PSC) attacks. Logic designs such as ring oscillator (RO) and time-to-digital converter (TDC) are used to measure the power consumed by security critical circuits, such as advanced encryption standard (AES). Firstly, the existing works require higher minimum traces for disclosure (MTD). Hence, in this work, we improve the sensitivity of the TDC-based sensors by manually placing the FPGA primitives inferring these sensors. This enhancement helps to determine the 128-bit AES key using 3.8K traces. Secondly, the existing defenses use ROs to defend against PSC attacks. However, cloud servers such as Amazon Web Services (AWS) block design with combinatorial loops. Hence, we propose a placement-based defense. We study the impact of (i) primitive-level placement on the AES design and (ii) additional logic that resides along with the AES on the correlation power analysis (CPA) attack results. Our results showcase that the AES along with filters and/or processors are sufficient to provide the same level or better security than the existing defenses.