Jekyll2026-04-15T15:24:22+00:00/feed.xmlCryptology and Data SecurityCryptology and data security research group, Institute of Computer Science, University of Bern.Cryptology and Data Security Research GroupWelcome Jonathan Bernhard2026-04-14T00:00:00+00:002026-04-14T00:00:00+00:00/2026/04/14/jonathan.bernhardIn April 2026 Jonathan Bernhard has become a member of the CRYPTO research group as a Ph.D. student. He previously completed a M.Sc. in Computer Science at the University of Fribourg and in the Swiss Joint Master of Computer Science, where he already worked on his thesis with the group. Welcome!

]]>Cryptology and Data Security Research GroupDigital Shaper 20262026-03-26T00:00:00+00:002026-03-26T00:00:00+00:00/2026/03/26/digital_shaperChristian Cachin has been named one of 100 Digital Shapers 2026 by Bilanz, the biweekly Swiss business magazine. The magazine recognized him in the category of Defenders for his research on secure protocols for cryptocurrencies.

]]>Cryptology and Data Security Research GroupWelcome Ulysse Pavloff2026-03-11T00:00:00+00:002026-03-11T00:00:00+00:00/2026/03/11/ulysse_pavloffUlysse Pavloff has joined the CRYPTO research group in March 2026 as a postdoctoral researcher. He completed his PhD in Computer Science at Paris-Saclay University in 2024 and specializes in blockchain and game theory. Welcome!

]]>Cryptology and Data Security Research GroupWorkshop on Secure Systems2026-01-16T00:00:00+00:002026-01-16T00:00:00+00:00/2026/01/16/workshop_secure_systemsThe Cryptology and Data Security Research Group organizes a workshop on the theme of secure systems :

University of Bern

16 February 2026

Hauptgebäude, Hochschulstrasse 4, Room 033

University of Bern

  Schedule
9:30 Christian Cachin, University of Bern
  Welcome
9:30-10:30 Peter Pietzuch, Imperial College London
  Keynote: Improving Cloud Security with Hardware Memory Capabilities
10:30-10:50 Break
11:00-11:30 François-Xavier Wicht, University of Bern
  Censorship-Resistant BitTorrent Trackers
11:30-12:00 Mpoki Mwaisela, University of Neuchatel
  IM-PIR: In-Memory Private Information Retrieval
   
12:15-14:00 Lunch (details to be announced)
   
14:00-14:45 Anil Kurmus, IBM Research - Zurich
  Speculative Memory Errors
14:45-15:15 Louis Vialar, University of Neuchatel
  SECUREFUSION: A Versatile Proxy for Transparent DBMS Encryption

Register here to attend

Advance registration is necessary until 12 February 2026.

]]>Cryptology and Data Security Research GroupNew results on asymmetric trust2025-12-16T00:00:00+00:002025-12-16T00:00:00+00:00/2025/12/16/asymmetric_modelThe asymmetric trust model lets each participant in a distributed system make its own trust assumptions about others, captured by an asymmetric quorum system. This contrasts with ordinary, symmetric quorum systems and threshold models, where trust assumptions are uniformly shared among participants. Fundamental problems like reliable broadcast and consensus are unsolvable in the asymmetric model if quorum systems satisfy only the classical properties of consistency and availability. Existing approaches overcome this by introducing stronger assumptions.

In recent work that was published at the OPODIS 2025 conference, CRYPTO team member Juan Villacis with coauthors Ignacio Amores Sesar from the University of Aarhus and Simon Holmgaard Kamp of Ruhr-Universität Bochum have shown that some of these assumptions are overly restrictive, so much so that they effectively eliminate the benefits of asymmetric trust. To address this, they have proposed a new approach to characterize asymmetric problems and, building upon it, they introduce algorithms for reliable broadcast and consensus that require weaker assumptions than previous solutions.

]]>Cryptology and Data Security Research GroupPh.D. degree for David Lehnherr2025-12-10T00:00:00+00:002025-12-10T00:00:00+00:00/2025/12/10/phd-davidDavid Lehnherr has successfully defended his Ph.D. thesis on 8 December 2025; the thesis is titled “Simplicial Structures for Epistemic Reasoning in Multi-agent Systems”. As the title reveals, this work is truly interdisciplinary and relates to logic and to distributed computing, spanning the fields between the research groups on Logic and Theory and Distributed Computing and Cryptography.

As external examiner Hans van Ditmarsch joined from CNRS, IRIT, University of Toulouse.

Congratulations!

David, Hans, Thomas, Christian

]]>Cryptology and Data Security Research GroupScaling privacy-preserving cryptocurrencies with toxic decoys2025-07-11T00:00:00+00:002025-07-11T00:00:00+00:00/2025/07/11/decoysThe research paper Toxic Decoys: A Path to Scaling Privacy-Preserving Cryptocurrencies has been accepted for publication in the Proceedings on Privacy Enhancing Technologies (PoPETs) and will be presented at corresponding symposium, PETS 2025, which takes place in Washington, DC, from July 14-19, 2025.

This work tackles the ever-growing storage demands of anonymous cryptocurrencies. It introduces a new scheme that randomly partitions the fresh outputs of transactions into fixed-size bins. Subsequent transactions reference these outputs when they transfer the tokens further.

The basic idea is that once a bin has been referenced as many times as its size, it can safely be pruned from the ledger. This preserves both privacy and security, but reduces the data that needs to be stored on the distributed ledger. Randomization ensures that attackers cannot predict in which bin an output will be placed. This prevents targeted flooding, allowing the system to scale by increasing the number of bins while remaining resilient under adversarial conditions. The research paper establishes this result by formally defining a cryptocurrency and its unpredictability, untraceability, and scalability notions. The work also presents a construction using Merkle trees that illustrates how partitioning and pruning are possible over a well-known authenticated data structure.

A detailed simulation of the new technique, using a transaction data set gathered from the Monero cryptocurrency, shows that the storage space can be reduced by approximately 60% while maintaining the same degree of privacy.

For more information, see this blog post that explains the approach in more depth.

This work appears in the Proceedings on Privacy Enhancing Technologies 2025. Congratulations to François-Xavier Wicht for this success.

]]>Cryptology and Data Security Research GroupDAG-based asymmetric consensus2025-06-11T00:00:00+00:002025-06-11T00:00:00+00:00/2025/06/11/asymmetric_dagThe research paper DAG-based Consensus with Asymmetric Trust has been accepted for presentation and publication at the PODC 2025 conference, the 44th ACM Symposium on Principles of Distributed Computing, which is held in Santa María Huatulco, Mexico, in June 2025. This work addresses the asymmetric-trust model, in which each participant is free to make its own subjective and individual trust assumptions about others. The paper shows the first asymmetric protocol for computing a common core, equivalent to that in the threshold model. Implementing this primitive then leads to the first randomized asynchronous DAG-based consensus protocol with asymmetric quorums,

Juan Villacis will present this work there – congratulations!

]]>Cryptology and Data Security Research GroupBest student paper award for David Lehnherr2025-05-22T00:00:00+00:002025-05-22T00:00:00+00:00/2025/05/22/best_paper_awardThe research paper Simplicial Belief has been accepted to the SIROCCO 2025 conference, the 32nd International Colloquium On Structural Information and Communication Complexity. SIROCCO is devoted to the study of the interplay between structural knowledge, communication, and computing in decentralized systems of multiple communicating entities.

More importantly, the paper has also won the best student paper award at SIROCCO 2025.

Congratulations to David Lehnherr!

]]>Cryptology and Data Security Research GroupSeminar on blockchains and cryptocurrencies2024-12-17T00:00:00+00:002024-12-17T00:00:00+00:00/2024/12/17/seminar_blockchainsIn the fall semester 2024, a seminar in the Joint Master in Computer Science at the University of Bern was offered by the CRYPTO group and focused on blockchains and cryptocurrencies.

The topics of the seminar were (many of) the most prominent Layer-1 and Layer-2 networks in the cryptocurrency domain. Every student participant or a team of two selected one cryptocurrency or blockchain and then presented its consensus protocol, the programming model, and other important aspects of the network. Every team also developed a sample application, like a smart contract, on the chosen platform and described it as part of a presentation.

The networks encompass cryptocurrencies, of which each is powered by a dedicated distributed ledger, and several acceleration protocols and support systems in the space. The latter typically achieve higher transaction throughput, supply critical information to cryptocurrency networks, or offer support for privacy. These networks are called “Layer 2” because their security usually relies on a “main” blockchain network at “Layer 1”.

The seminar was led by Jayamine Alupotha and Christian Cachin and the results of the seminar, with presentations and sample projects, are available online from our gitlab.

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