Dummy-Free Deterministic CTIDH Boosts Isogeny Cryptography

The new dummy‑free dCTIDH implementation (dCTIDH‑2048‑194 and dCTIDH‑2048‑205) reaches median evaluation times of 1.59–1.60 Gcyc, a ~5% speed boost over CTIDH and four‑times faster than dCSIDH. getnews.me/dummy-free-deterministic... #isogeny #postquantum

Leuven Isogeny Days 6 — 10/11/12 September 2025 – ISOCRYPT

There's still a bit of time to register for the Leuven Isogeny Days 6, go to www.esat.kuleuven.be/cosic/projec... for info & registration!
#isogeny #isogenies #isocrypt

Registration for the Leuven Isogeny Days 6 is now open!
📅 10–12 Sept 2025 @ KU Leuven
Morning: research talks
Afternoon: brainstorming sessions
More info: www.esat.kuleuven.be/cosic/projec...
#isogeny #isocrypt #erc #postquantum

Let us walk on the 3-isogeny graph: efficient, fast, and simple Constructing and implementing isogeny-based cryptographic primitives is an active research. In particular, performing length-$n$ isogenies walks over quadratic field extensions of $\mathbb{F}_p$ plays an exciting role in some constructions, including Hash functions, Verifiable Delay Functions, Key-Encapsulation Mechanisms, and generic proof systems for isogeny knowledge. Remarkably, many isogeny-based constructions, for efficiency, perform $2$-isogenies through square root calculations. This work analyzes the idea of using $3$-isogenies instead of $2$-isogenies, which replaces the requirement of calculating square roots with cube roots. Performing length-$m$ $3$-isogenies allows shorter isogeny walks than when employing length-$n$ $2$-isogenies since a cube root calculation costs essentially the same as computing a square root, and we require $3^m \approx 2^n$ to provide the same security level. We propose an efficient mapping from arbitrary supersingular Montgomery curves defined over $\mathbb{F}_{p^2}$ to the $3$-isogeny curve model from Castryck, Decru, and Vercauteren (Asiacrypt 2020); a deterministic algorithm to compute all order-$3$ points on arbitrary supersingular Montgomery curves, and an efficient algorithm to compute length-$m$ $3$-isogeny chains. We improve the length-$m$ $3$-isogeny walks required by the KEM from Nakagawa and Onuki (CRYPTO 2024) by using our results and introducing more suitable parameter sets that are friendly with C-code implementations. In particular, our experiments illustrate an improvement of 26.41\%--35.60\% in savings when calculating length-$m$ $3$-isogeny chains and using our proposed parameters instead of those proposed by Nakagawa and Onuki (CRYPTO 2024). Finally, we enhance the key generation of $\mathsf{CTIDH}$-2048 by including radical $3$-isogeny chains over the basefield $\mathbb{F}_p$, reducing the overhead of finding a $3$-torsion basis as required in some instantiations of the $\mathsf{CSIDH}$ protocol. Our experiments illustrate the advantage of radical $3$ isogenies in the key generation of $\mathsf{CTIDH}$-2048, with an improvement close to 4x faster than the original $\mathsf{dCTIDH}$.

If 3-isogeny walks replace square roots with cube roots at equal cost, isn't security *cubed* not doubled? Is this efficiency or a security downgrade disguised as progress? 💥 #crypto #isogeny #recursion eprint.iacr.org/2025...

Leuven Isogeny Days 5 — 11/12/13 September 2024 – ISOCRYPT

This week in COSIC... We are hosting the 5th edition of the Leuven #Isogeny Days. The workshop consists of a mix of research talks during the morning, and brainstorming sessions in the afternoon.
#isocrypt #isocryptproject #erc #ercisocrypt
www.esat.kuleuven.be/cosic/projec...