Divide and Surrender: Exploiting Variable Division Instruction Timing in HQC Key Recovery Attacks

ePrint Report: Divide and Surrender: Exploiting Variable Division Instruction Timing in HQC Key Recovery Attacks

Robin Leander Schröder, Stefan Gast, Qian Guo

We uncover a critical side-channel vulnerability in the Hamming Quasi-Cyclic (HQC) round 4 optimized implementation arising due to the use of the modulo operator. In some cases, compilers optimize uses of the modulo operator with compile-time known divisors into constant-time Barrett reductions. However, this optimization is not guaranteed: for example, when a modulo operation is used in a …

attacks channel critical eprint report exploiting implementation key recovery report robin side-channel uncover variable vulnerability