[Resource Topic] 2023/1618: Improved algorithms for finding fixed-degree isogenies between supersingular elliptic curves

Welcome to the resource topic for 2023/1618

Title:
Improved algorithms for finding fixed-degree isogenies between supersingular elliptic curves

Authors: Benjamin Benčina, Péter Kutas, Simon-Philipp Merz, Christophe Petit, Miha Stopar, Charlotte Weitkämper

Abstract:

Finding isogenies between supersingular elliptic curves is a natural algorithmic problem which is known to be equivalent to computing the curves’ endomorphism rings.
When the isogeny is additionally required to have a specific degree d, the problem appears to be somewhat different in nature, yet it is also considered a hard problem in isogeny-based cryptography.
Let E_1,E_2 be supersingular elliptic curves over \mathbb{F}_{p^2}. We present improved classical and quantum algorithms that compute an isogeny of degree d between E_1 and E_2 if it exists. Let the sought-after degree be d = p^{1/2+ \epsilon} for some \epsilon>0.
Our essentially memory-free algorithms have better time complexity than meet-in-the-middle algorithms, which require exponential memory storage, in the range 1/2\leq\epsilon\leq 3/4 on a classical computer and quantum improvements in the range 0<\epsilon<5/2.

ePrint: https://eprint.iacr.org/2023/1618

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