Faster Constant-Time Decoder for MDPC Codes and Applications to BIKE KEM

BIKE is a code-based key encapsulation mechanism (KEM) that was recently selected as an alternate candidate by the NIST’s standardization process on post-quantum cryptography. This KEM based Niederreiter scheme instantiated with QC-MDPC codes, and it uses BGF decoder for decapsulation. We discovered important limitations of we describe in detail, then propose new decoding algorithm codes called PickyFix. Our two auxiliary iterations are significantly different from previous approaches show how they can be implemented efficiently. analyze our respect to both its error correction capacity performance practice. When compared BGF, constant-time implementation PickyFix achieves speedups 1.18, 1.29, 1.47 security levels 128, 192 256, respectively.