Mikhail Kudinov

YouTube video by Nadim Kobeissi Nadim Kobeissi's Applied Cryptography Course

I made a video about my upcoming applied cryptography course: youtu.be/z6kK7rIbyB0

Crypto 2025 is just around the corner! Check out the full program here:
crypto.iacr.org/2025/program...

Join us on Monday for our talk where we explore the tradeoffs of hash-based signatures.

We then apply these findings to propose post-quantum Ethereum PoS signatures:
eprint.iacr.org/2025/1332

Abstract. In this note, we present a new instantiation of the hash-based multi-signature framework introduced by Drake, Khovratovich, Kudinov, and Wagner (CiC Vol 2 Issue 1, eprint 2025/055) for Ethereum’s consensus layer. Inspired by a recent work of Khovratovich, Kudinov, and Wagner (Crypto 2025, eprint 2025/889), we instantiate the framework with a novel incomparable encoding that improves the tradeoff between signature size and verification hashing. The purpose of this document is to make explicit how to use the ideas of the latter work within the framework of Drake, Khovratovich, Kudinov, and Wagner.

Technical Note: LeanSig for Post-Quantum Ethereum (Justin Drake, Dmitry Khovratovich, Mikhail Kudinov, Benedikt Wagner) ia.cr/2025/1332

I am rereading the comics. These are great an so many new ones came out :)

The EU wants to decrypt your private data by 2030 The EU Commission unveiled the first step in its security strategy to ensure "lawful and effective" law enforcement access to data

This battle will keep playing out over and over again until they achieve something that their own citizens have made it clear they don’t want. www.techradar.com/vpn/vpn-priv...

You never asked 😅

YouTube video by PewDiePie I'm DONE with Google

PewDiePie’s evolution into a tech geek is so cool! His recent video dives deep into privacy concerns and surveillance issues, while being still fun to watch. I think these are the topics that couldn’t be more relevant today. Highly recommend watching his take on it:

🔗 youtu.be/u_Lxkt50xOg?...

Single author, fifteen pages, reduces the bit complexity of millenia-old UOV instances!!

A touchpad is also acceptable, but if you are using a mouse, why would you use Apple’s? :)

Apple announces that TLS client connections in version 26+ will be using hybrid PQ X25519MLKEM768 by default

support.apple.com/en-us/122756

A nice 127 pages read 🥲

Abstract. Hash-based signatures have been studied for decades and have recently gained renewed attention due to their post-quantum security. At the core of the most prominent hash-based signature schemes, XMSS and SPHINCS+, lies a one-time signature scheme based on hash chains due to Winternitz. In this scheme, messages are encoded into vectors of positions (i.e., vertices in a hypercube) in the hash chains, and the signature contains the respective chain elements. The encoding process is crucial for the efficiency and security of this construction. In particular, it determines a tradeoff between signature size and computational costs. Researchers have been trying to improve this size-time tradeoff curve for decades, but all improvements have been arguably marginal. In this work, we revisit the encoding process with the goal of minimizing verification costs and signature sizes. As our first result, we present a novel lower bound for the verification cost given a fixed signature size. Our lower bound is the first to directly apply to general encodings including randomized, non-uniform, and non-injective ones. Then, we present new encodings and prove their security. Inspired by our lower bound, these encodings follow a counterintuitive approach: we map messages non-uniformly into the top layers of a much bigger hypercube than needed but the encoding itself has (hard to find) collisions. With this, we get a 20 % to 40 % improvement in the verification cost of the signature while keeping the same security level and the same size. Our constructions can be directly plugged into any signature scheme based on hash chains, which includes SPHINCS+ and XMSS.

Image showing part 2 of abstract.

At the Top of the Hypercube – Better Size-Time Tradeoffs for Hash-Based Signatures (Dmitry Khovratovich, Mikhail Kudinov, Benedikt Wagner) ia.cr/2025/889

Will there be a recording?

Hacking Cryptography Learn how the good guys implement cryptography and how the bad guys exploit it.</b> Everything we do in the digital world is protected by cryptography. But when pure math and algorithms are implement...

Great initiative!

Saw some references for Go. Can I suggest a recent one: www.manning.com/books/hackin...

Excited to be heading to #Eurocrypt2025 in Madrid soon!

I’ll be speaking at Algebraic Hash Cryptanalysis Days on Security Requirements in the Context of Hash-Based Signatures.

Catch me at the affiliated events or during the main conference. Let’s connect! #Cryptography #Madrid

YouTube video by PQCrypto conference videos Treating Dishonest Ciphertexts in Post Quantum KEMs – Explicit vs Implicit Rejection in the FO T

🎤 My talk from #PQCrypto2025 is now live on YouTube!

I discussed rejection types in KEMs. Why they matter, how they impact security and which one should you choose.

Check it out & let me know your thoughts! 👇
📺 youtu.be/W-gUd_qTUs4?...

#PostQuantum #Cryptography #KEMs

Did they discuss the applications?

That looks amazing!

And the announcement of the
2025 IACR Test-of-Time Award for Eurocrypt is completing the post and goes to: "On Ideal Lattices and Learning with Errors over Rings", by V. Lyubashevsky, C. Peikert & O. Regev. More info at: iacr.org/testoftime
Congratulations!

Basic Lattice Cryptography: The concepts behind Kyber (ML-KEM) and Dilithium (ML-DSA) This tutorial focuses on describing the fundamental mathematical concepts and design decisions used in the two ``main'' lattice schemes standardized by NIST and included in the CNSA 2.0 algorithmic su...

2/2 Pair this with Lyubashevsky’s latest primer on Kyber/Dilithium fundamentals (eprint.iacr.org/2024/1287) for a full picture of lattice cryptography’s state-of-the-art!

1/2 🔐 Exciting read: "A Survey on the Security of Lattice-Based NIST Finalists" (eprint.iacr.org/2025/304.pdf) provides a clear overview of modern security analysis for Lattice-based schemes. It dives into structured vs. unstructured attacks on LWE/NTRU assumptions and reduction algorithms like BKZ.

Cool! Thanks. I will take a look

That is a nice discovery! Adding to my read list!

My Crypto Learning Journey: Helpful Resources

I’ve compiled a list of materials that helped me the most in my cryptography journey. The list will keep growing—feel free to suggest your favorites!

error0024.github.io/posts/2025/0...

Abstract. In this paper, we present an improved framework for proving query bounds in the Quantum Random Oracle Model (QROM) for algorithms with both quantum and classical query interfaces, where the classical input is partially controlled by the adversary. By extending existing techniques, we develop a method to bound the progress an adversary can make with such partial-control classical queries. While this framework is applicable to different hash function properties, we decided to demonstrate the impact of the new techniques by giving an analysis of the multi-target extended target collision resistance property (m-eTCR). This new approach allows us to achieve an improved bound that significantly reduces the required function key size. Our proof is tight in terms of query complexity and has significant implications for cryptographic applications, especially for signature schemes in the hash & sign paradigm, enabling more efficient instantiations with reduced salt sizes and smaller signature lengths. For an example of multiple signatures aggregation, we achieve a signature size of 30 kB smaller.

Hybrid-query bounds with partial input control - framework and application to tight M-eTCR (Andreas Hülsing, Mikhail Kudinov, Christian Majenz) ia.cr/2025/633

Abstract. In this work we revisit the post-quantum security of KEM-based password-authenticated key exchange (PAKE), specifically that of (O)CAKE. So far, these schemes evaded a security proof considering quantum adversaries. We give a detailed analysis of why this is the case, determining the missing proof techniques. To this end, we first provide a proof of security in the post-quantum setting, up to a single gap. This proof already turns out to be technically involved, requiring advanced techniques to reason in the QROM, including the compressed oracle and the extractable QROM. To pave the way towards closing the gap, we then further identify an efficient simulator for the ideal cipher. This provides certain programming abilities as a necessary and sufficient condition to close the gap in the proof: we demonstrate that we can close the gap using the simulator, and give a meta-reduction based on KEM-anonymity that shows the impossibility of a non-programming reduction that covers a class of KEMs that includes Kyber / ML-KEM.

CAKE requires programming - On the provable post-quantum security of (O)CAKE (Kathrin Hövelmanns, Andreas Hülsing, Mikhail Kudinov, Silvia Ritsch) ia.cr/2025/458

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