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Jonas Janneck

@jonasjanneck.bsky.social

PhD Student in Cryptography at Ruhr University Bochum

6 Posts83 Follower 103 Folgt

Nils Fleischhacker @cryptomaeher.bsky.social · last mo.

I'm looking for a job! I'm an experienced researcher in cryptography. My focus is on the transition to post-quantum cryptographic protocols and protocols related to blockains. If that sounds like someone you might want to hire or you know someone who might, let's talk!

Nils Fleischhacker @cryptomaeher.bsky.social · 3mo ago

My time at RUB is coming to an end and I'm looking for an industry position. Primarily looking for remote or Rhine-Ruhr area positions, but will consider any exceptional offers. So if you're looking to hire a cryptographer to work on cryptographic protocols, or related areas, maybe we should talk!

Sabine Oechsner @proofnerd.bsky.social · 4mo ago

I'm looking for a PhD student to work with me on formal verification for cryptographic protocols. This is a 4-year position at VU Amsterdam, co-supervised with Kristina Sojakova. Send me an email if you want to know more!

Julian Loss @julianloss.bsky.social · 5mo ago

Consider attending our CASA summer school on cryptography and distributed computing from June 22.-25. in Bochum! Registration is open until March 12. casa.rub.de/en/events/ca...

CASA Summer School | Cluster of Excellence CASA | RUB

The annual summer school offers young scientists lectures by high-ranking scientists and international exchange.

casa.rub.de

Doreen Riepel @doreenriepel.bsky.social · 5mo ago

I am very excited that our work on secure cloud storage is now online. A big shoutout also to my co-author @jonasjanneck.bsky.social who will present the results at Eurocrypt’26!

ePrint Updates@eprint.ing.bot · 5mo ago

Secure Cloud Storage: Modularization, Network Adversaries and Adaptive Corruptions (Jonas Janneck, Doreen Riepel) ia.cr/2026/434

Abstract. End-to-end cloud storage solutions are deployed at large scale, yet recent works have demonstrated severe attacks against their confidentiality and integrity. Motivated by this, a first formal treatment of secure cloud storage was given at CRYPTO 2024 by Backendal, Davis, Günther, Haller and Paterson (BDGHP). They define syntax and security notions, capturing client-to-client security of cloud storage schemes with respect to a password distribution. They also give an eﬃcient construction using the Two-Hash Diﬃe-Hellman (2HDH) OPRF and standard cryptographic building blocks, which they prove secure under selective corruptions in the random oracle model. However, several aspects of practical security guarantees remain open. We extend and refine the work of BDGHP along multiple dimensions, advancing the analysis of secure cloud storage schemes. First, we prove that their construction can be proven secure against adaptive corruptions (with a slight modification), circumventing technical challenges posed by file sharing. Second, we modularize the scheme further by introducing an abstraction for the authentication procedure. This allows us to identify the concrete role of 2HDH and alternative instantiations. Third, we introduce a weaker model that captures adversaries who can arbitrarily control the network, except during registration. This allows us to prove concrete guarantees about online password guessing attacks, whereas the stronger model inherently allows for oﬄine guessing. Finally, we formalize and prove explicit authentication, relying on the security of our new authentication abstraction and the MAC scheme, where the latter was previously not used in the security analysis.

Jonas Janneck @jonasjanneck.bsky.social · 5mo ago

We updated our work on the first concrete security proof of the Falcon signature scheme 🦅 ia.cr/2024/1769 This is joint work with Pierre-Alain, Phillip, Hubert, and @kiltz.bsky.social and will appear at Eurocrypt’26 🎉

A Closer Look at Falcon

Falcon is a winner of NIST’s six-year post-quantum cryptography standardisation competition. Based on the celebrated full-domain-hash framework of Gentry, Peikert and Vaikuntanathan (GPV) (STOC’08), F...

ia.cr

Jonas Janneck @jonasjanneck.bsky.social · 5mo ago

Happy to announce that Bird of Prey is accepted at EC’26 🛸✍️🎉 eprint.iacr.org/2025/1844 The paper presents three signature combiners for PQC migration preserving strong unforgeability. They capture all broadly used classical schemes and can be used with *any* PQ signature in a black-box way!

Bird of Prey: Practical Signature Combiners Preserving Strong Unforgeability

Following the announcement of the first winners of the NIST post-quantum cryptography standardization process in 2022, cryptographic protocols are now undergoing migration to the newly standardized sc...

eprint.iacr.org

Tjerand Silde @tjesi.bsky.social · 6mo ago

I am co-organising (with @drl3c7er.bsky.social and Lucjan Hanzlik) a workshop on Privacy-Enhancing Cryptography in Rome on May 10 as an affiliated event to IACR Eurocrypt. Submit your best PEC-work (3-page extended abstract) for presentation by February 25th: privcryptworkshop.github.io

PrivCrypt 2026

privcryptworkshop.github.io

Doreen Riepel @doreenriepel.bsky.social · 6mo ago

Planning your trip to Eurocrypt or looking for an excuse to still go? The reviewers did not appreciate your too involved or too elegant proofs? Consider submitting a talk to ProTeCS (protecs-workshop.gitlab.io), an affiliated event of EC, where we celebrate proofs as independent objects of study!

Call for Presentations

Workshop on Proofs and Proof Techniques for Cryptographic Security. Affiliated with Eurocrypt 2026.

protecs-workshop.gitlab.io

Jonas Janneck @jonasjanneck.bsky.social · 10mo ago

Are you looking for a signature combiner for PQC migration? We already have combiners/hybrids for unforgeability. But do we have combiners that also preserve strong unforgeability and all BUFF properties? Now we do:

ePrint Updates@eprint.ing.bot · 10mo ago

Bird of Prey: Practical Signature Combiners Preserving Strong Unforgeability (Jonas Janneck) ia.cr/2025/1844

Abstract. Following the announcement of the first winners of the NIST post-quantum cryptography standardization process in 2022, cryptographic protocols are now undergoing migration to the newly standardized schemes. In most cases, this transition is realized through a hybrid approach, in which algorithms based on classical hardness assumptions, such as the discrete logarithm problem, are combined with post-quantum algorithms that rely on quantum-resistant assumptions, such as the Short Integer Solution (SIS) problem. A combiner for signature schemes can be obtained by simply concatenating the signatures of both schemes. This construction preserves unforgeability of the underlying schemes; however, it does not extend to stronger notions, such as strong unforgeability. Several applications, including authenticated key exchange and secure messaging, inherently require strong unforgeability, yet no existing combiner is known to achieve this property. This work introduces three practical combiners that preserve strong unforgeability and all BUFF (beyond unforgeability features) properties. Each combiner is tailored to a specific class of classical signature schemes capturing all broadly used schemes that are strongly unforgeable. Remarkably, all combiners can be instantiated with any post-quantum signature scheme in a black-box way making deployment practical and significantly less error prone. The proposed solutions are further highly efficient and have signatures that are at most the size of the (insecure) concatenation combiner. For instance, our most efficient combiner enables the combination of EdDSA with ML-DSA, yielding a signature size that is smaller than the sum of an individual EdDSA signature and an individual ML-DSA signature. Additionally, we identify a novel signature property that we call random-message validity and show that it can be used to replace the BUFF transform with the more efficient Pornin-Stern transform. The notion may be of independent interest.

ePrint Updates @eprint.ing.bot · 12mo ago

Snake Mackerel: An Isogeny-Based AKEM Leveraging Randomness Reuse (Jonas Janneck, Jonas Meers, Massimo Ostuzzi, Doreen Riepel) ia.cr/2025/1474

Abstract. An Authenticated Key Encapsulation Mechanism (AKEM) combines public-key encryption and digital signatures to provide confidentiality and authenticity. AKEMs build the core of Hybrid Public Key Encryption (RFC 9180) and serve as a useful abstraction for messaging applications like the Messaging Layer Security (MLS) protocol (RFC 9420) and Signal’s X3DH protocol. To date, most existing AKEM constructions either rely on classical (non post-quantum) assumptions or on unoptimized black-box approaches leading to suboptimal efficiency.

In this work, we choose a different abstraction level to combine KEMs and identification schemes more efficiently by leveraging randomness reuse. We construct a generic scheme and identify the necessary security requirements on the underlying KEM and identification scheme when reusing parts of their randomness. This allows for a concrete instantiation from isogenies based on the POKÉ KEM (EUROCRYPT’25) and the SQIsignHD identification scheme (EUROCRYPT’24). To be used in our black-box construction, the identification scheme requires the more advanced security property of response non-malleability. Hence, we further show that a slight modification of SQIsignHD satisfies this notion, which might be of independent interest.

Putting everything together, our final scheme yields the most compact AKEM from PQ assumptions with public keys of 366 bytes and ciphertexts of 216 bytes while fulfilling the strongest confidentiality and authenticity notions.

Miro Haller @mirohaller.bsky.social · last yr.

The preliminary program for the Cryptographic Applications Workshop (CAW) at Eurocrypt'25 is out. #CAW focuses on the construction and analysis of cryptography built for practice. This thread gives a quick overview; the full program and abstracts are here: caw.cryptanalysis.fun#program

Peter Schwabe @cryptojedi.bsky.social · last yr.

The 3rd edition of WISC – Women in Security and Cryptography Workshop will take place in Bochum from June 16 to 18. Already confirmed are talks by Lejla Batina, Zinaida Benenson, Shafi Goldwasser, Martina Lindorfer, and Doreen Riepel. Registration is open now! casa.rub.de/en/events/wi...

WISC | Cluster of Excellence CASA | RUB

The Women in Security and Cryptography Workshop promotes international female PhD students and outstanding female students in the field of IT security.

casa.rub.de