Side-Channel Leakage in Low-Entropy Masking Schemes Attributed to FPGA Architecture

Masking is one of the most popular to guarantee the security of the cryptographic implementation against side-channel analysis. Low Entropy Masking Scheme (LEMS) has been proposed to relieve the high overhead by reducing the entropy of the mask. The masks are selected carefully to resist univariate first-order attacks. However, in practice, securely implementing masking can be a challenging task. In this work, we exhibit the vulnerability of LEMS implementation on FPGA. Firstly, we provide the security model to characterize the masking balance at the implementation level. Based on the security model, we exhibit a first-order leakage in the netlist of the implementation. It can be proved that this defect is due to the uncontrollable EDA tool to optimize the AES Sbox implementation on the specific architecture of FPGA during synthesis. The discovered flaw can be exhibited by performing a couple of first-order attacks to recover the secret key successfully on FPGA. The vulnerability is verified by simulation and practical measurements. Finally, the potential countermeasure and security evaluation process for LEMS are provided to avoid leakage during the pre-silicon design phase.