Input | Output co-hosts ‘Cryptographic tools for blockchains' workshop at Eurocrypt ‘25

The conference featured a highly competitive selection process, with just 123 papers accepted from a total of 624 submissions. These contributions were compiled into eight volumes of Springer’s Lecture Notes in Computer Science, spanning key areas such as secure multiparty computation, public-key cryptography, advanced cryptographic protocols, zero-knowledge proofs, and applied cryptography.

Noteworthy highlights included IBM’s work on the cryptanalysis of SNOVA and the development of compact public-key encryption schemes leveraging higher-dimensional isogenies. The event was co-organized by the IMDEA Software Institute, Universidad Carlos III de Madrid, and Universidad Complutense de Madrid, and was generously supported by major technology sponsors including Apple, Google, Huawei, and IBM, and Midnight.

The CTB workshop: advancing blockchain cryptography

Capitalizing on Input | Output (IO)’s established presence in Spain supported the co-organization of the ‘Cryptographic Tools for Blockchains’ (CTB’25) workshop as a satellite event to Eurocrypt. This workshop marked the second edition of the CTB series, following the inaugural CTB’24 held in Zürich, Switzerland.

The CTB workshops are organized in collaboration with prominent research institutions—in this edition, with the Consejo Superior de Investigaciones Científicas (CSIC) - Spain’s national research council) and Universidad de Málaga. Both editions of CTB were explicitly designed to operate without formal proceedings, enabling speakers to present cutting-edge ideas and engage in constructive, in-person dialogue rather than adhering to the constraints of traditional publication formats.

CTB’25 attracted a broad cross-section of researchers and practitioners dedicated to advancing the cryptographic foundations of blockchain technology. The program featured 10 talks, comprising eight peer-submitted presentations and two guest keynote lectures. These were grouped into three thematic areas: cryptographic primitives and protocols, consensus mechanisms, and time-related cryptographic primitives. This thematic structuring facilitated coherent discussion while recognizing the inherently interdisciplinary nature of cryptographic research.

Key technical highlights from CTB’25

In the cryptographic primitives and protocols track, standout contributions included:

• Refinement-based Verification of Protocols with Quantitative Values by Aoxuan Li and Itsaka Rakotonirina, showcasing a verification tool built atop Tamarin that supports time-sensitive predicates—particularly relevant for bridge protocols employing timelocks.
• Homomorphic Signature-based Witness Encryption and Applications by Alireza Kavousi and István András Seres, introducing a homomorphic variant of SWE to enhance efficiency and deployment of SWE-dependent applications such as secure voting and auctions.
• Dynamic-FROST: Schnorr Threshold Signatures with a Flexible Committee by Annalisa Cimatti et al., presenting an extension to FROST enabling dynamic adjustment of signers and threshold requirements, opening new possibilities for decentralized governance and consensus protocols.
• Jigsaw: Doubly Private Smart Contracts by Sanjam Garg et al., proposing a novel framework for smart contracts that ensures privacy both on-chain and off-chain, addressing long-standing challenges in privacy-preserving computation.

The consensus mechanisms track featured:

• Putting Sybils on a Diet: Securing Distributed Hash Tables using Proofs of Space by Christoph U. Günther and Krzysztof Pietrzak, highlighting how proofs of space can mitigate Sybil attacks in distributed hash tables more effectively than traditional proof-of-work mechanisms.
• Nakamoto Consensus from Multiple Resources by Mirza Ahad Baig et al., proposing a taxonomy of consensus models leveraging multiple resource types—such as work, space, and sequential evaluation—and their applicability to longest-chain protocols.

In the time-based cryptographic primitives track, key contributions included:

• Traceable Verifiable Random Functions by Dan Boneh, Aditi Partap, and Lior Rotem, introducing a novel VRF variant incorporating traceability, allowing accountability for the generation of random outputs in decentralized settings.
• A Tale of Time Release Powered by Blockchain and IBE by Stella Wohnig et al., offering a comprehensive exploration of how time release encryption can be realized by combining blockchain technologies with Identity-Based Encryption (IBE), promising advanced functionality in blockchain ecosystems.

Guest keynotes and community engagement

CTB’25 also featured two high-profile guest talks. Nicola Greco of FileOz delivered an engaging presentation titled Public Good Crypto: Funding Last-Mile Cryptography Research to Secure the Internet and Push Digital Human Rights Forward, outlining current funding opportunities supporting foundational cryptography research. Daniel Slamanig from Universität der Bundeswehr München offered a sweeping historical and technical overview of Anonymous Credentials: Past, Present and Future, including their evolving role in European digital identity frameworks and connections to self-sovereign identity initiatives.

All presentations were followed by lively Q&A sessions and in-depth discussions that often extended into informal, offline interactions. Approximately 50 attendees were present throughout the day, reflecting strong community interest and engagement—nearing the 64 registrants who expressed initial intent to participate. The workshop’s format encouraged active exchange, with many proposals and ideas poised to evolve into concrete tools or serve as foundational building blocks for advanced blockchain functionalities.

Looking ahead

CTB continues to provide a vital platform for researchers and practitioners to exchange insights, showcase innovations, and debate the future of cryptography in blockchain systems. By convening global experts and fostering an open, collaborative environment, CTB workshops contribute to advancing the security, scalability, and functionality of blockchain technologies. Interested readers and contributors are encouraged to visit the workshop website for presentation slides and updates. IO' looks forward to supporting and participating in future editions of CTB, continuing its commitment to advancing cryptographic research and its practical applications in decentralized ecosystems.