And Hell
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And Hell
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Reposted by And Hell
gustavosbanegas.bsky.social
Dummy or not dummy? That’s the question — and our answer is no dummy at all! 🧠🔒

Our paper “Hardened CTIDH: Dummy-Free and Deterministic CTIDH” has been accepted at INDOCRYPT 2025
Preprint here: eprint.iacr.org/2025/1645/
Hardened CTIDH: Dummy-Free and Deterministic CTIDH
Isogeny-based cryptography has emerged as a promising post-quantum alternative, with CSIDH and its constant-time variants \ctidh and \dctidh offering efficient group-action protocols. However, \ctid...
eprint.iacr.org
October 13, 2025 at 9:08 AM
Reposted by And Hell
eprint.ing.bot
Hardened CTIDH: Dummy-Free and Deterministic CTIDH (Gustavo Banegas, Andreas Hellenbrand, Matheus Saldanha) ia.cr/2025/1645
Abstract. Isogeny-based cryptography has emerged as a promising post-quantum alternative, with CSIDH and its constant-time variants and offering efficient group-action protocols. However, and~rely on dummy operations in differential addition chains (DACs) and Matryoshka, which can be exploitable by fault-injection attacks. In this work, we present the first implementation of . Our approach combines two recent ideas: , which enforces equal-length DACs within each batch without padding, and a reformulated Matryoshka structure that removes dummy multiplications and validates all intermediate points. Our analysis shows that small primes such as 3, 5, and 7 severely restrict feasible configurations, motivating new parameter sets that exclude them. We implement dummy-free -194 and -205, achieving group action costs of roughly 357, 000–362, 000 $\Fp$-multiplications, with median evaluation times of 1.59–1.60 (Gcyc). These results do not surpass , but they outperform by roughly 5% while eliminating dummy operations entirely. Compared to dCSIDH, our construction is more than 4× faster. To the best of our knowledge, this is the first implementation of a CSIDH-like protocol that is simultaneously deterministic, constant-time, and fully dummy-free. Image showing part 2 of abstract.
September 12, 2025 at 2:37 PM
Reposted by And Hell
dfaranha.bsky.social
The EU wants to spend your money to assemble a giant mass surveillance machine with little effect on harm against children. Chat Control is not effective, weakens security for all and does not respect privacy. Contact your EU representatives and let them know.

csa-scientist-open-letter.org/Sep2025
csa-scientist-open-letter.org
September 9, 2025 at 11:24 AM
Reposted by And Hell
krijn.isogeni.es
Finally, a state-of-the-art version of CTIDH! That is, deterministic and a prime of 2048 bits. We introduce a new batching strategy we call "wombats", making dCTIDH five times faster than deterministic CSIDH. Surprisingly, it even beats "non-deterministic" CTIDH.

See eprint.iacr.org/2025/107
dCTIDH: Fast & Deterministic CTIDH
This paper presents dCTIDH, a CSIDH implementation that combines two recent developments into a novel state-of-the-art deterministic implementation. We combine the approach of deterministic variants o...
eprint.iacr.org
January 23, 2025 at 9:24 PM