Cryptology ePrint Archive: Report 2019/1423

QC-MDPC decoders with several shades of gray

Nir Drucker and Shay Gueron and Dusan Kostic

Abstract: QC-MDPC code-based KEMs rely on decoders that have a small or even negligible Decoding Failure Rate (DFR). These decoders should be efficient and implementable in constant-time. One example for a QC-MDPC KEM is the Round-2 candidate of the NIST PQC standardization project, "BIKE". We have recently shown that the Black-Gray decoder achieves the required properties. In this paper, we deffine several new variants of the Black-Gray decoder. One of them, called Black-Gray-Flip, needs only 7 steps to achieve a smaller DFR than Black-Gray with 9 steps, for the same block size. On current AVX512 platforms, our BIKE-1 (Level-1) constant-time decapsulation is 1:9x faster than the previous decapsulation with Black-Gray. We also report an additional 1:25x decapsulating speedup using the new AVX512-VBMI2 and vector-PCLMULQDQ instructions available on "Ice-Lake" micro-architecture.

Category / Keywords: public-key cryptography / BIKE, QC-MDPC codes, constant-time implementation, QC-MDPC decoders

Date: received 7 Dec 2019

Contact author: drucker nir at gmail com,shay gueron@gmail com,dusan kostic@epfl ch

Available format(s): PDF | BibTeX Citation

Version: 20191210:075801 (All versions of this report)

Short URL: ia.cr/2019/1423


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