QC-MDPC Decoders with Several Shades of Gray

Nir Drucker, Shay Gueron, Dusan Kostic

Research output: Chapter in Book/Report/Conference proceedingConference contributionpeer-review


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 define 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 currentplatforms, our BIKE-1 (Level-1) constant-time decapsulation is (Formula Presented) faster than the previous decapsulation with Black-Gray. We also report an additional (Formula Presented) decapsulating speedup using the newandinstructions available on “Ice-Lake” micro-architecture.

Original languageEnglish
Title of host publicationPost-Quantum Cryptography - 11th International Conference, PQCrypto 2020, Proceedings
EditorsJintai Ding, Jean-Pierre Tillich
Number of pages16
ISBN (Print)9783030442224
StatePublished - 2020
Event11th International Conference on Post-Quantum Cryptography, PQCrypto 2020 - Paris, France
Duration: 15 Apr 202017 Apr 2020

Publication series

NameLecture Notes in Computer Science (including subseries Lecture Notes in Artificial Intelligence and Lecture Notes in Bioinformatics)
Volume12100 LNCS
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349


Conference11th International Conference on Post-Quantum Cryptography, PQCrypto 2020

Bibliographical note

Publisher Copyright:
© 2020, Springer Nature Switzerland AG.


  • BIKE
  • Constant-time implementation
  • QC-MDPC codes
  • QC-MDPC decoders

ASJC Scopus subject areas

  • Theoretical Computer Science
  • General Computer Science


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