Damien Robert
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damienrobert.bsky.social
Damien Robert
@damienrobert.bsky.social
270 followers 160 following 53 posts
Researcher in algorithmic number theory, notably on abelian varieties and their moduli spaces, and their applications to elliptic and isogeny based cryptography
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Reposted by Damien Robert
stefanotessaro.bsky.social
And now we are famous: www.nytimes.com/2025/11/21/w... - congratulations to all colleagues who made the NYT (both through quotes, by playing a role, or by being on this picture)
November 22, 2025 at 5:35 AM
Reposted by Damien Robert
gro-tsen.bsky.social
If anyone wants to learn a broad overview of computability theory and Turing degrees, I recommend Soare's 2016 book “Turing Computability: Theory and Applications” (not to be confused with his 1987 book, “Recursively Enumerable Sets and Degrees”, which is much denser!).
November 16, 2025 at 10:37 AM
Reposted by Damien Robert
gro-tsen.bsky.social
I thought the notion of “sheaf for a Lawvere-Tierney topology” was a very complicated one, but I realized it's actually not so complicated, and it can be defined completely internally (i.e., you don't need to know what a topos is, just how constructive math works). •1/7
November 9, 2025 at 10:18 AM
Reposted by Damien Robert
jeanas.bsky.social
I'm happy to hear that Egbert Rijke's book “Introduction to Homotopy Type Theory” is finally published by Cambridge University Press!

www.cambridge.org/us/universit...
Introduction to Homotopy Type Theory | Cambridge University Press & Assessment
www.cambridge.org
October 31, 2025 at 4:55 PM
Reposted by Damien Robert
jonathan.isogeny.club
TL;DR: See title 🥳
eprint.ing.bot ePrint Updates @eprint.ing.bot · Oct 8
qt-Pegasis: Simpler and Faster Effective Class Group Actions (Pierrick Dartois, Jonathan Komada Eriksen, Riccardo Invernizzi, Frederik Vercauteren) ia.cr/2025/1859
Abstract. In this paper, we revisit the recent PEGASIS algorithm that computes an effective group action of the class group of any imaginary quadratic order R on a set of supersingular elliptic curves primitively oriented by R. Although PEGASIS was the first algorithm showing the practicality of computing unrestricted class group actions at higher security levels, it is complicated and prone to failures, which leads to many rerandomizations. In this work, we present a new algorithm, qt-Pegasis, which is much simpler, but at the same time faster and removes the need for rerandomization of the ideal we want to act with, since it never fails. It leverages the main technique of the recent qlapoti approach. However, qlapoti solves a norm equation in a quaternion algebra, which corresponds to the full endomorphism ring of a supersingular elliptic curve. We show that the algorithm still applies in the quadratic setting, by embedding the quadratic ideal into a quaternion ideal using a technique similar to the one applied in KLaPoTi. This way, we can reinterpret the output of qlapoti as four equivalent quadratic ideals, instead of two equivalent quaternion ideals. We then show how to construct a Clapoti-like diagram in dimension 2, which embeds the action of the ideal in a 4-dimensional isogeny. We implemented our qt-Pegasis algorithm in SageMath for the CSURF group action, and we achieve a speedup over PEGASIS of 1.8× for the 500-bit parameters and 2.6× for the 4000-bit parameters. Image showing part 2 of abstract.
October 8, 2025 at 8:17 AM
Reposted by Damien Robert
maria.isogeny.club
The Isogeny Club Season 7 starts today! At 5pm CEST, Bruno Sterner will talk about finding large smooth twins from short lattice vectors. More details at isogeny.club
September 23, 2025 at 7:23 AM
Reposted by Damien Robert
krijn.isogeni.es
Announcing The Isogeny Problems!

A curated list of the seven foremost unsolved problems in isogeny-based cryptography. Solving one of these profound questions would mark a monumental advance, and as a resolver you'd get eternal honor and epic rewards!

Full list: isogeni.es/problems
The Isogeny Problems
isogeni.es
September 15, 2025 at 7:43 AM
Reposted by Damien Robert
maria.isogeny.club
TL;DR: we solve norm equations in a better way and get around a 2x improvement to IdealToIsogeny routines crucial in both SQIsign and PRISM.
eprint.ing.bot ePrint Updates @eprint.ing.bot · Sep 11
Qlapoti: Simple and Efficient Translation of Quaternion Ideals to Isogenies (Giacomo Borin, Maria Corte-Real Santos, Jonathan Komada Eriksen, Riccardo Invernizzi, Marzio Mula, Sina Schaeffler, Frederik Vercauteren) ia.cr/2025/1604
Abstract. The main building block in isogeny-based cryptography is an algorithmic version of the Deuring correspondence, called IdealToIsogeny. This algorithm takes as input left ideals of the endomorphism ring of a supersingular elliptic curve and computes the associated isogeny. Building on ideas from QFESTA, the Clapoti framework by Page and Robert reduces this problem to solving a certain norm equation. The current state of the art is however unable to efficiently solve this equation, and resorts to a relaxed version of it instead. This impacts not only the efficiency of the IdealToIsogeny procedure, but also its success probability. The latter issue has to be mitigated with complex and memory-heavy rerandomization procedures, but still leaves a gap between the security analysis and the actual implementation of cryptographic schemes employing IdealToIsogeny as a subroutine. For instance, in SQIsign the failure probability is still 2⁻⁶⁰ which is not cryptographically negligible. The main contribution of this paper is a very simple and efficient algorithm called Qlapoti which approaches the norm equation from Clapoti directly, solving all the aforementioned problems at once. First, it makes the IdealToIsogeny subroutine between 2.2 and 2.6 times faster. This signigicantly improves the speed of schemes using this subroutine, including notably SQIsign and . On top of that, Qlapoti has a cryptographically negligible failure probability. This eliminates the need for rerandomization, drastically reducing memory consumption, and allows for cleaner security reductions. Image showing part 2 of abstract.
September 12, 2025 at 2:00 PM
Reposted by Damien Robert
cosic.bsky.social
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
June 16, 2025 at 6:17 AM
Reposted by Damien Robert
andreavbasso.bsky.social
We (finally) published all the material from this course on SQIsign, including lecture slides and exercise sheets for the Sage laboratory. Available here: github.com/andreavico/S...
June 10, 2025 at 3:58 PM
Reposted by Damien Robert
milenerioux.bsky.social
📢 #1MinuteAvec ... ⏰
Alice Pellet-Mary au pays des codes secrets et de la #cryptographie.
Portrait à découvrir de cette chercheuse de l'équipe #Canari du Centre #Inria de l' @univbordeaux.bsky.social qui partage avec nous son #parcours et son #métier !

👉 youtu.be/LKRy8bO5x8E?...
May 23, 2025 at 12:12 PM
Reposted by Damien Robert
gro-tsen.bsky.social
A kind of social variant of the man-in-the-middle attack: 🧵🔽
edent.tel Terence Eden @edent.tel · May 3
You receive a call on your phone.

The caller says they're from your bank and they're calling about a suspected fraudulent payment.

"Oh yeah," you think. Obvious scam, right?

The caller says "I'll send you an in-app notification to prove I'm calling from your bank."

🧵 1/4
May 3, 2025 at 9:03 PM
Reposted by Damien Robert
krijn.isogeni.es
New work: we explain cubical arithmetic in simple terms to show you how easy it is to compute pairings. Essentially, you only need to know the Montgomery ladder!

As a bonus, pairings from cubical arithmetic are faster than those from Miller's loop for applications in isogeny-based cryptography.
eprint.ing.bot ePrint Updates @eprint.ing.bot · Apr 15
Simpler and Faster Pairings from the Montgomery Ladder (Giacomo Pope, Krijn Reijnders, Damien Robert, Alessandro Sferlazza, Benjamin Smith) ia.cr/2025/672
Abstract. We show that Montgomery ladders compute pairings as a by-product, and explain how a small adjustment to the ladder results in simple and efficient algorithms for the Weil and Tate pairing on elliptic curves using cubical arithmetic. We demonstrate the efficiency of the resulting cubical pairings in several applications from isogeny-based cryptography. Cubical pairings are simpler and more performant than pairings computed using Miller’s algorithm: we get a speed-up of over 40% for use-cases in SQIsign, and a speed-up of about 7% for use-cases in CSIDH. While these results arise from a deep connection to biextensions and cubical arithmetic, in this article we keep things as concrete (and digestible) as possible. We provide a concise and complete introduction to cubical arithmetic as an appendix.
April 15, 2025 at 12:34 PM
Reposted by Damien Robert
bsky.defeo.lu
Yes! RWC ❤️ Number Theory.

Congrats to the CADO-NFS team!
rwc.iacr.org Real World Crypto Symposium @rwc.iacr.org · Mar 26
The second Levchin Prize goes to the CADO-NFS team: Emmanuel Thomé, Pierrick Gaudry, and Paul Zimmerman! Congratulations!

#realworldcrypto
March 26, 2025 at 2:44 PM
Reposted by Damien Robert
bsky.defeo.lu
Registration to the SQIparty is open, free, and we have a first sketch of a program!

www.cig.udl.cat/SQIparty2025...

Register and plan your travel quickly: the rooms are reserved only until Thursday!

See you in Lleida!
bsky.defeo.lu Luca De Feo @bsky.defeo.lu · Mar 13
Fancy some isogeny crypto?

Join us for a 3-day workshop on isogeny-based cryptography in Lleida, Catalonia, April 28-30

www.cig.udl.cat/icrypto2025_...

Brought to you by ULleida's Cryptography+Graphs group, the SQIsign team and friends!

Registration and program coming soon
Registration is free!
Cathedral of La Seu Vella in Lleida
March 25, 2025 at 5:04 PM
Reposted by Damien Robert
milenerioux.bsky.social
🔊 Le 19/03 c'est la journée internationale du #Canari 🪶!

Le jour idéal pour vous partager des infos sur notre équipe (du même nom) qui conçoit des #algorithmes pour la sécurité des données au service de la #cryptographie #postquantique 🌐!

↪️ www.inria.fr/fr/canari-pr...
↪️ www.inria.fr/fr/canari
Canari : une nouvelle équipe Inria au service de la protection de nos données
Comment sécuriser un monde numérique qui ne cesse de se densifier et de se complexifier ? C’est le défi que va relever Canari, une nouvelle équipe d’Inria, grâce à la conception d’outils algorithmique...
www.inria.fr
March 19, 2025 at 11:26 AM
Reposted by Damien Robert
krijn.isogeni.es
> claims no new results
> adds in a tiny new result anyway
> ???

anyway, enjoy the read!
eprint.ing.bot ePrint Updates @eprint.ing.bot · Mar 14
A Note on the Advanced Use of the Tate Pairing (Krijn Reijnders) ia.cr/2025/477
Abstract. This short note explains how the Tate pairing can be used to efficiently sample torsion points with precise requirements, and other applications. These applications are most clearly explained on Montgomery curves, using the Tate pairing of degree 2, but hold more generally for any degree or abelian variety, or even generalized Tate pairings. This note is explanatory in nature; it does not contain new results, but aims to provide a clear and concise explanation of results in the literature that are somewhat hidden, yet are extremely useful in practical isogeny-based cryptography.
March 14, 2025 at 8:07 AM
Reposted by Damien Robert
bsky.defeo.lu
Fancy some isogeny crypto?

Join us for a 3-day workshop on isogeny-based cryptography in Lleida, Catalonia, April 28-30

www.cig.udl.cat/icrypto2025_...

Brought to you by ULleida's Cryptography+Graphs group, the SQIsign team and friends!

Registration and program coming soon
Registration is free!
Cathedral of La Seu Vella in Lleida
March 13, 2025 at 5:30 PM
Reposted by Damien Robert
jonathan.isogeny.club
GG everyone who played #KalmarCTF 2025!

Writeups for my two challs:

MonoDOOM: jonathke.github.io/monoDOOM
A chal based on a sick sidechannel attack by @damienrobert.bsky.social !

Not-so-complex multiplication: jonathke.github.io/not-so-complex
An easy chal based on complex multiplication.
Jonathan Komada Eriksen - Notes
jonathke.github.io
March 9, 2025 at 5:24 PM
Reposted by Damien Robert
krijn.isogeni.es
Absolutely thrilled for season six of the Isogeny Club (isogeny.club) starting February 25th by a talk by Abel Laval!
The Isogeny Club
isogeny.club
February 4, 2025 at 10:27 AM
Reposted by Damien Robert
maria.isogeny.club
Really excited to finally share PRISM, a new isogeny-based signature 🥳 joint work with lots of awesome people.

eprint.iacr.org/2025/135
PRISM: Simple And Compact Identification and Signatures From Large Prime Degree Isogenies
The problem of computing an isogeny of large prime degree from a supersingular elliptic curve of unknown endomorphism ring is assumed to be hard both for classical as well as quantum computers. In thi...
eprint.iacr.org
January 29, 2025 at 8:34 AM
Reposted by Damien Robert
milenerioux.bsky.social
Pour la Journée internationale de la #protection des #données, coup de projecteur sur les travaux novateurs de l'équipe-projet #Canari.

🧐 Son domaine de recherche ? Les protocoles et #algorithmes de #cryptographie #postquantique !

👉 www.inria.fr/fr/securite-...
cc @damienrobert.bsky.social
Sécuriser nos données à l’ère du quantique, un défi de taille
À l’occasion de la Journée internationale de la protection des données, coup de projecteur sur les travaux novateurs de l'équipe-projet Canari. Son domaine de recherche : les protocoles et algorithmes...
www.inria.fr
January 28, 2025 at 9:41 AM
Reposted by Damien Robert
milenerioux.bsky.social
Le #logiciel PARI/GP, système de calcul formel pour la théorie des nombres, a reçu le #Prix science ouverte du #logiciel libre 2024 pour la catégorie « communauté ».
👋 à Aurel Page de l'équipe #Canari et aux scientifiques de l' #IMB impliqués !

t.co/oWqHxweG24

cc @damienrobert.bsky.social
https://www.insmi.cnrs.fr/fr/cnrsinfo/prix-science-ouverte-logiciel-libre-parigp
t.co
January 20, 2025 at 1:36 PM
damienrobert.bsky.social
I was today years old when I realized we can build twists of X as a pullback from the classifying stack BAut(X).

Why didn't anyone ever tell me?! This simplifies so many arguments about twists!

(Shamelessly copying Krijn's post: bsky.app/profile/krij...)
krijn.isogeni.es Krijn Reijnders @krijn.isogeni.es · Nov 12
I was today years old when I learned that adding by (0,0) on a Montgomery curve is simply x --> 1/x

Why didn't anyone ever tell me?!
November 24, 2024 at 6:01 PM
damienrobert.bsky.social
Nice paper!
arxiv.org/abs/2411.11566
Rubik's as a Galois'
We prove that the Rubik's cube group can be realized as a Galois group over the rationals.
arxiv.org
November 20, 2024 at 8:10 AM