HARE: Compact HQC via Distance-Informed Erasure Decoding

Tianrui Wang; Qicheng Teng; Anyu Wang; Jun Zhang; Bo Pang; Chunhuan Zhao; Sihuang Hu; Xiaoyun Wang

Paper 2026/544

HARE: Compact HQC via Distance-Informed Erasure Decoding

Tianrui Wang, Tsinghua University

Qicheng Teng, Tsinghua University

Anyu Wang, Tsinghua University

Jun Zhang, Capital Normal University

Bo Pang, ICBC Software Development Center

Chunhuan Zhao, Huawei Technologies

Sihuang Hu, Shandong University

Xiaoyun Wang, Tsinghua University

Abstract

We present HARE, a key encapsulation mechanism (KEM) scheme based on the Hamming Quasi-Cyclic (HQC) framework that achieves substantially reduced public key and ciphertext sizes. HARE focuses on two complementary techniques: a novel distance-informed erasure decoding method for the concatenated code and ciphertext compression based on covering codes. The distance-informed erasure decoding method uses distance information from the inner Reed-Muller decoder to identify unreliable local blocks and treats them as erasures for the outer Reed-Solomon decoder.This improves decoding performance and enables more compact code parameters. For ciphertext compression, HARE adopts a covering-code perspective and maps the ciphertext vector to a nearby codeword with a shorter representation. The use of the Kaikkonen-Rosendahl code provides a more favorable bandwidth trade-off than previously considered Hamming and Golay code constructions. Combining these techniques, HARE reduces the combined size of the public key and ciphertext by 15.4%, 14.8%, and 15.3% at NIST security categories 1, 3, and 5, respectively, compared with HQC.

Note: Update the DFR model and the parameter data

Metadata

Available format(s): PDF
Category: Public-key cryptography
Publication info: Preprint.
Keywords: Post-Quantum Cryptography Code-Based Cryptography Hamming Quasi-Cyclic HARE Erasure Decoding Covering Codes
Contact author(s): wangtr22 @ mails tsinghua edu cn
tqc21 @ mails tsinghua edu cn
anyuwang @ tsinghua edu cn
junz @ cnu edu cn
pangb21 @ sdc icbc com cn
zhaochunhuan @ huawei com
husihuang @ gmail com
xiaoyunwang @ tsinghua edu cn
History: 2026-09-17: last of 5 revisions; 2026-03-19: received; See all versions
Short URL: https://ia.cr/2026/544
License: CC BY

BibTeX

@misc{cryptoeprint:2026/544,
      author = {Tianrui Wang and Qicheng Teng and Anyu Wang and Jun Zhang and Bo Pang and Chunhuan Zhao and Sihuang Hu and Xiaoyun Wang},
      title = {{HARE}: Compact {HQC} via Distance-Informed Erasure Decoding},
      howpublished = {Cryptology {ePrint} Archive, Paper 2026/544},
      year = {2026},
      url = {https://eprint.iacr.org/2026/544}
}