Dominic Deuber

I am an IT security researcher focusing on anonymity, privacy and cryptocurrencies. In particular, I am interested in topics at the interface of technology and law, which is why I started to study law in 2018 alongside my research.

In 2023, I received my Ph.D. (Dr.-Ing.) at the Chair of Applied Cryptography, Friedrich-Alexander-Universität Erlangen-Nürnberg, under the supervision of Dominique Schröder. During my Ph.D., I was fortunate to be part of the Research Training Group 2475: Cybercrime and Forensic Computing by the Deutsche Forschungsgemeinschaft (DFG). Besides, I am grateful that I had the opportunity to join and collaborate with Nicolas Christin and his group at Carnegie Mellon University (CMU).

In 2017, I received my M.Sc. in computer science from Saarland University, where I also graduated in 2015 with a B.Sc. in bioinformatics (majoring in computational molecular biology). During my studies, I worked as a student trainee in software development and as a research assistant at the Helmholtz Center for Information Security (CISPA).

selected publications

2023

Assessing Anonymity Techniques Employed in German Court Decisions: A De-Anonymization Experiment

Dominic Deuber, Michael Keuchen, and Nicolas Christin

In Proceedings of the 32nd USENIX Security Symposium (USENIX Security ’23), 2023

Abstract URL Talk

Democracy requires transparency. Consequently, courts of law must publish their decisions. At the same time, the interests of the persons involved in these court decisions must be protected. For this reason, court decisions in Europe are anonymized using a variety of techniques. To understand how well these techniques protect the persons involved, we conducted an empirical experiment with 54 law students, whom we asked to de-anonymize 50 German court decisions. We found that all anonymization techniques used in these court decisions were vulnerable, most notably the use of initials. Since even supposedly secure anonymization techniques proved vulnerable, our work empirically reveals the complexity involved in the anonymization of court decisions, and thus calls for further research to increase anonymity while preserving comprehensibility. Toward that end, we provide recommendations for improving anonymization quality. Finally, we provide an empirical notion of “reasonable effort,” to flesh out the definition of anonymity in the legal context. In doing so, we bridge the gap between the technical and the legal understandings of anonymity.

2022

SoK: Assumptions Underlying Cryptocurrency Deanonymizations

Dominic Deuber, Viktoria Ronge, and Christian Rückert

In Proceedings of the Privacy Enhancing Technologies Symposium (PETS 2022), 2022

Abstract URL Talk

In recent years, cryptocurrencies have increasingly been used in cybercrime and have become the key means of payment in darknet marketplaces, partly due to their alleged anonymity. Furthermore, the research attacking the anonymity of even those cryptocurrencies that claim to offer anonymity by design is growing and is being applied by law enforcement agencies in the fight against cybercrime. Their investigative measures require a certain degree of suspicion and it is unclear whether findings resulting from attacks on cryptocurrencies’ anonymity can indeed establish that required degree of suspicion. The reason for this is that these attacks are partly based upon uncertain assumptions which are often not properly addressed in the corresponding papers. To close this gap, we extract the assumptions in papers that are attacking Bitcoin, Monero and Zcash, major cryptocurrencies used in darknet markets which have also received the most attention from researchers. We develop a taxonomy to capture the different nature of those assumptions in order to help investigators to better assess whether the required degree of suspicion for specific investigative measures could be established. We found that assumptions based on user behaviour are in general the most unreliable and thus any findings of attacks based on them might not allow for intense investigative measures such as pre-trial detention. We hope to raise awareness of the problem so that in the future there will be fewer unlawful investigations based upon uncertain assumptions and thus fewer human rights violations.

2021

CoinJoin in the Wild - An Empirical Analysis in Dash

Dominic Deuber, and Dominique Schröder

In Proceedings of the 26th European Symposium on Research in Computer Security (ESORICS 2021), 2021

Abstract URL

CoinJoin is the predominant means to enhance privacy in non-private cryptocurrencies, such as Bitcoin. The basic idea of CoinJoin is to create transactions that combine equal-valued coins of multiple users. This mixing of coins aims to prevent linkage of the users’ transactional in- and outputs. The cryptocurrency Dash employs a built-in CoinJoin service and, therefore, is ideal for empirically studying CoinJoin. This paper presents the first empirical analysis of Dash, which reveals that over 40 % of all private transactions can be de-anonymized depending on underlying assumptions. The main issue of these attacks is the coin-aggregation problem, i.e. the need to combine outputs of several CoinJoin transactions. The coin aggregation problem is not specific to Dash and affects other cryptocurrencies as empirical evidence in Bitcoin suggests. We show that the logical solution to the problem, namely CoinJoin transactions with non-fixed arbitrary values, suffers from other privacy weaknesses. We propose a novel mixing algorithm to mitigate the need for coin aggregation without introducing additional privacy vulnerabilities. In contrast to prior mixing algorithms, our approach removes the need for fixed values by dynamically creating equal-valued CoinJoin transactions. The mixing algorithm is not specific to Dash, and integration into other cryptocurrencies, especially into Bitcoin, is possible.

2020

Minting Mechanism for Proof of Stake Blockchains

Dominic Deuber, Nico Döttling, Bernardo Magri, Giulio Malavolta, and Sri Aravinda Krishnan Thyagarajan

In Proceedings of the 18th International Conference on Applied Cryptography and Network Security (ACNS 2020), 2020

Abstract URL

As an alternative for the computational waste generated by proof-of-work (PoW) blockchains, proof-of-stake (PoS) systems gained a lot of popularity, being adopted by many existing cryptocurrencies. Unfortunately, as we show, PoS-based currencies, where newly minted coins are assigned to the slot leader, inevitably incentivises coin hoarding, as players maximise their utility by holding their stakes and not trading. As a result, existing PoS-based cryptocurrencies do not mimic the properties of fiat currencies, but are rather regarded as investment vectors.

In this work we initiate the study of minting mechanisms in cryptocurrencies as a primitive on its own right, and as a first step to a solution to mitigate coin hoarding in PoS currencies we propose a novel minting mechanism based on waiting-time first-price auctions. Our main technical tool is a protocol to run an auction over any blockchain. Moreover, our protocol is the first to securely implement an auction without requiring a semi-trusted party, i.e., where every miner in the network is a potential bidder. Our approach is generically applicable and we show that it is incentive-compatible with the underlying blockchain, i.e., the best strategy for a player is to behave honestly. Our proof-of-concept implementation shows that our system is efficient and scales to tens of thousands of bidders.

2019

My Genome Belongs to Me: Controlling Third Party Computation on Genomic Data

Dominic Deuber, Christoph Egger, Katharina Fech, Giulio Malavolta, Dominique Schröder, Sri Aravinda Krishnan Thyagarajan, Florian Battke, and Claudia Durand

In Proceedings of the Privacy Enhancing Technologies Symposium (PETS 2019), 2019

Abstract URL

An individual’s genetic information is possibly the most valuable personal information. While knowledge of a person’s DNA sequence can facilitate the diagnosis of several heritable diseases and allow personalized treatment, its exposure comes with significant threats to the patient’s privacy. Currently known solutions for privacy-respecting computation require the owner of the DNA to either be heavily involved in the execution of a cryptographic protocol or to completely outsource the access control to a third party. This motivates the demand for cryptographic protocols which enable computation over encrypted genomic data while keeping the owner of the genome in full control. We envision a scenario where data owners can exercise arbitrary and dynamic access policies, depending on the intended use of the analysis results and on the credentials of who is conducting the analysis. At the same time, they are not required to maintain a local copy of their entire genetic data and do not need to exhaust their computational resources in an expensive cryptographic protocol.

In this work, we present METIS, a system that assists the computation over encrypted data stored in the cloud while leaving the decision on admissible computations to the data owner. A critical feature of our system is that the data owner is free from computational overload and her communication complexity is independent of the size of the input data and only linear in the size of the circuit’s output. METIS is based on garbled circuits and supports any polynomially-computable function. We demonstrate the practicality of our approach with an implementation and an evaluation of several functions over real dataset.
Redactable Blockchain in the Permissionless Setting

Dominic Deuber, Bernardo Magri, and Sri Aravinda Krishnan Thyagarajan

In Proceedings of the 40th IEEE Symposium on Security and Privacy (Oakland 2019), 2019

Abstract URL

Bitcoin is an immutable permissionless blockchain system that has been extensively used as a public bulletin board by many different applications that heavily relies on its immutability. However, Bitcoin’s immutability is not without its fair share of demerits. Interpol exposed the existence of harmful and potentially illegal documents, images and links in the Bitcoin blockchain, and since then there have been several qualitative and quantitative analysis on the types of data currently residing in the Bitcoin blockchain. Although there is a lot of attention on blockchains, surprisingly the previous solutions proposed for data redaction in the permissionless setting are far from feasible, and require additional trust assumptions. Hence, the problem of harmful data still poses a huge challenge for law enforcement agencies like Interpol (Tziakouris, IEEE S&P’18).

We propose the first efficient redactable blockchain for the permissionless setting that is easily integrable into Bitcoin, and that does not rely on heavy cryptographic tools or trust assumptions. Our protocol uses a consensus-based voting and is parameterised by a policy that dictates the requirements and constraints for the redactions; if a redaction gathers enough votes the operation is performed on the chain. As an extra feature, our protocol offers public verifiability and accountability for the redacted chain. Moreover, we provide formal security definitions and proofs showing that our protocol is secure against redactions that were not agreed by consensus. Additionally, we show the viability of our approach with a proof-of-concept implementation that shows only a tiny overhead in the chain validation of our protocol when compared to an immutable one.

2018

Functional Credentials

Dominic Deuber, Matteo Maffei, Giulio Malavolta, Max Rabkin, Dominique Schröder, and Mark Simkin

In Proceedings on Privacy Enhancing Technologies Symposium (PETS 2018), 2018

Abstract URL

A functional credential allows a user to anonymously prove possession of a set of attributes that fulfills a certain policy. The policies are arbitrary polynomially computable predicates that are evaluated over arbitrary attributes. The key feature of this primitive is the delegation of verification to third parties, called designated verifiers. The delegation protects the privacy of the policy: A designated verifier can verify that a user satisfies a certain policy without learning anything about the policy itself. We illustrate the usefulness of this property in different applications, including outsourced databases with access control. We present a new framework to construct functional credentials that does not require (non-interactive) zero-knowledge proofs. This is important in settings where the statements are complex and thus the resulting zero-knowledge proofs are not efficient. Our construction is based on any predicate encryption scheme and the security relies on standard assumptions. A complexity analysis and an experimental evaluation confirm the practicality of our approach.