Cryptology ePrint Archive: Report 2021/655

On the Effect of Projection on Rank Attacks in Multivariate Cryptography

Morten Øygarden and Daniel Smith-Tone and Javier Verbel

Abstract: The multivariate scheme HFEv- used to be considered a promising candidate for a post-quantum signature system. First suggested in the early 2000s, a version of the scheme made it to the third round of the ongoing NIST post-quantum standardization process. In late 2020, the system suffered from an efficient rank attack due to Tao, Petzoldt, and Ding. In this paper, we inspect how this recent rank attack is affected by the projection modification. This modification was introduced to secure the signature scheme PFLASH against its predecessor's attacks. We prove upper bounds for the rank of projected HFEv- (pHFEv-) and PFLASH under the new attack, which are tight for the experiments we have performed. We conclude that projection could be a useful tool in protecting against this recent cryptanalysis.

Category / Keywords: public-key cryptography / post-quantum cryptography, multivariate cryptography, minrank

Original Publication (in the same form): PQCrypto 2021

Date: received 19 May 2021

Contact author: morten oygarden at simula no, daniel smith at nist gov, Javier Verbel at tii ae

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Version: 20210520:203136 (All versions of this report)

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