International Association
for Cryptologic Research

Chou suggested a constant-time implementation for quasi-cyclic moderatedensity parity-check (QC-MDPC) code-based cryptography to mitigate timing attacks at CHES 2016. This countermeasure was later found to become vulnerable to a differential power analysis (DPA) in private syndrome computation, as described by Rossi et al. at CHES 2017. The proposed DPA, however, still could not completely recover accurate secret indices, requiring further solving linear equations to obtain entire secret information. In this paper, we propose a multiple-trace attack which enables to completely recover accurate secret indices. We further propose a singletrace attack which can even work when using ephemeral keys or applying Rossi et al.’s DPA countermeasures. Our experiments show that the BIKE and LEDAcrypt may become vulnerable to our proposed attacks. The experiments are conducted using power consumption traces measured from ChipWhisperer-Lite XMEGA (8-bit processor) and ChipWhisperer UFO STM32F3 (32-bit processor) target boards.