[Resource Topic] 2019/150: QcBits: Constant-Time Small-Key Code-Based Cryptography

Welcome to the resource topic for 2019/150

QcBits: Constant-Time Small-Key Code-Based Cryptography

Authors: Tung Chou


This paper introduces a constant-time implementation for a quasi-cyclic moderate-density-parity-check (QC-MDPC) code based encryption scheme. At a 2^{80} security level, the software takes 14679937 Cortex-M4 and 1560072 Haswell cycles to decrypt a short message, while the previous records were 18416012 and 3104624 (non-constant-time) cycles. Such speed is achieved by combining two techniques: 1) performing each polynomial multiplication in \mathbb{F}_2[x]/(x^r-1) and \mathbb{Z}[x]/(x^r-1) using a sequence of ``constant-time rotations’’ and 2) bitslicing.

ePrint: https://eprint.iacr.org/2019/150

Talk: https://www.youtube.com/watch?v=_MRyFfLzybw

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