[Resource Topic] 2022/1283: A Note on Reimplementing the Castryck-Decru Attack and Lessons Learned for SageMath

Welcome to the resource topic for 2022/1283

Title:
A Note on Reimplementing the Castryck-Decru Attack and Lessons Learned for SageMath

Authors: Rémy Oudompheng, Giacomo Pope

Abstract:

This note describes the implementation of the Castryck-Decru key recovery attack on SIDH using the computer algebra system, SageMath. We describe in detail alternate computation methods for the isogeny steps of the original attack ((2,2)-isogenies from a product of elliptic curves and from a Jacobian), using explicit formulas to compute values of these isogenies at given points, motivated by both performance considerations and working around SageMath limitations. A performance analysis is provided, with focus given to the various algorithmic and SageMath specific improvements made during development, which in total accumulated in approximately an eight-fold performance improvement compared with a naïve reimplementation of the proof of concept.

ePrint: https://eprint.iacr.org/2022/1283

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