Practical Attack on All Parameters of the HPPC Signature Scheme

Published

January 2, 2026

Author(s)

Pierre Briaud, Maxime Bros, Ray Perlner, Daniel Smith-Tone

Abstract

HPPC is a multivariate signature scheme submitted to the NIST PQC standardization process in response to the recent call for additional signature schemes. We show that, despite some non-standard notational choices in the submission document, HPPC can be viewed as a special case of the well-studied, but broken for all practical parameters, HFE signature scheme. We further show that the HPPC construction introduces additional structure that further weakens the scheme. For instance, the central map has Q-rank 2 independently from the degree D of the central polynomial that is used. Using these observations, we show that HPPC is weaker against the direct attack than claimed in the submission document and more crucially that all parameter sets can be practically broken using MinRank techniques. For instance, with a very naive implementation, we have been able to recover an equivalent key in approximately 8 min for security level 2, an hour and a half for security level 4, and slightly more than 7 h for security level 5.

Conference Dates

August 13-15, 2025

Conference Location

Toronto, CA

Conference Title

Selected Areas in Cryptography (SAC 2025)

Pub Type

Conferences

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DOI Link

Keywords

cryptanalysis, post-quantum cryptography, signature schemes

Citation

Briaud, P. , Bros, M. , Perlner, R. and Smith-Tone, D. (2026), Practical Attack on All Parameters of the HPPC Signature Scheme, Selected Areas in Cryptography (SAC 2025), Toronto, CA, [online], https://doi.org/10.1007/978-3-032-10536-3_19 (Accessed January 8, 2026)