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 KEM scheme based on the HQC framework with reduced public key and ciphertext sizes. HARE combines four optimization techniques: (i) a novel distance-informed erasure decoding method for the concatenated code, (ii) ciphertext compression enhanced with covering codes, refining the approach of Bitzer et al. in EUROCRYPT 2026, (iii) unbalanced parameter choices, and (iv) a more accurate error distribution model for decryption failure analysis. Among these, the key innovation is the distance-informed erasure decoding technique, which leverages distance information from the inner code to identify unreliable blocks and treat them as erasures that are subsequently corrected by the outer code. This significantly lowers the decryption failure rate and enables more compact parameter sets. Combining these techniques, HARE achieves substantially improved compactness compared to HQC, reducing the combined size of the public key and ciphertext by 15.5%, 14.8%, and 15.2% at NIST security levels 1, 3, and 5, respectively.

Note: Fix the parameter data

Metadata

Available format(s): PDF
Category: Cryptographic protocols
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: 2026-06-17: last of 4 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}
}