M-SIDH and MD-SIDH: countering SIDH attacks by masking information

Tako Boris Fouotsa*, Tomoki Moriya, Christophe Petit

*Corresponding author for this work

Research output: Chapter in Book/Report/Conference proceedingConference contribution

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Abstract

The SIDH protocol is an isogeny-based key exchange protocol using supersingular isogenies, designed by Jao and De Feo in 2011. The protocol underlies the SIKE algorithm which advanced to the fourth round of NIST’s post-quantum standardization project in May 2022. The algorithm was considered very promising: indeed the most significant attacks against SIDH were meet-in-the-middle variants with exponential complexity, and torsion point attacks which only applied to unbalanced parameters (and in particular, not to SIKE).

This security picture dramatically changed in August 2022 with new attacks by Castryck-Decru, Maino-Martindale and Robert. Like prior attacks on unbalanced versions, these new attacks exploit torsion point information provided in the SIDH protocol. Crucially however, the new attacks embed the isogeny problem into a similar isogeny problem in a higher dimension to also affect the balanced parameters. As a result of these works, the SIKE algorithm is now fully broken both in theory and in practice.

Given the considerable interest attracted by SIKE and related protocols in recent years, it is natural to seek countermeasures to the new attacks. In this paper, we introduce two such countermeasures based on partially hiding the isogeny degrees and torsion point information in the SIDH protocol. We present a preliminary analysis of the resulting schemes including non-trivial generalizations of prior attacks. Based on this analysis we suggest parameters for our M-SIDH variant with public key sizes of 4434, 7037 and 9750 bytes respectively for NIST security levels 1, 3, 5.
Original languageEnglish
Title of host publicationAdvances in Cryptology – EUROCRYPT 2023
Subtitle of host publication42nd Annual International Conference on the Theory and Applications of Cryptographic Techniques, Lyon, France, April 23-27, 2023, Proceedings
EditorsCarmit Hazay, Martijn Stam
PublisherSpringer
Pages282-309
Edition1
ISBN (Electronic)978-3-031-30589-4
ISBN (Print)978-3-031-30588-7
DOIs
Publication statusE-pub ahead of print - 16 Apr 2023
Event42nd Annual International Conference on the Theory and Applications of Cryptographic Techniques - Lyon, France
Duration: 23 Apr 202327 Apr 2023

Publication series

NameLecture Notes in Computer Science
PublisherSpringer
Volume14008
ISSN (Print)0302-9743
ISSN (Electronic)1611-3349

Conference

Conference42nd Annual International Conference on the Theory and Applications of Cryptographic Techniques
Abbreviated titleEUROCRYPT 2023
Country/TerritoryFrance
CityLyon
Period23/04/2327/04/23

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