arXiv subjects

Markulf Kohlweiss

Publications and source records attributed to Markulf Kohlweiss.

3 recordsLinked to original sources

arXiv2026

UC, Categorically: Rigorous Diagrammatic Proofs

Category theory is a mathematical theory of composition, widely used in logic, computing, and physics. Here we apply it to give a theory of secure composition. In particular, we provide a categorical treatment of Canetti's Universal Composability (UC) framework for systems with a static number of parties and sessions, often termed UC for static systems, yielding four benefits. First, we present our results graphically yet retain rigor by applying a standard categorical technique known as string diagrams. In particular, our formulation of the composition theorem can be graphically verified with a short sequence of diagrams, while remaining translatable to equations and amenable to formal verification. Second, categories let us generalize so that our results extend beyond interactive Turing machines to other forms of computation, such as quantum computation or domain-specific languages. Third, categories help us drop some unnecessary restrictions of UC (e.g., our adversary can be a computational network rather than a single Turing machine); we prove equivalence between our variant and the usual UC, showing no expressiveness is lost. Finally, the categorical perspective leads us to identify and correct some minor technical oversights in the standard formulation of simple UC.

cs.LO↗

arXiv2022

Bottom-up Trust Registry in Self Sovereign Identity

Self sovereign identity is a form of decentralised credential management. During credential verification, data exchange only happens between the data owner and the verifier without passing through any third parties. While this approach offers a privacy-centric solution, it poses a challenge. How do verifiers trust that the credential is vouched by a trusted source? More specifically, how do verifiers know that the issuer has the reputation or is authorised to issue the credential? In this paper, we propose a trust registry design that handles the aspect of human trust in self sovereign identity. We also introduce an incentivisation mechanism for the trust registry in order to motivate each stakeholder to participate actively and honestly.

cs.CR↗

arXiv2017

Multiparty Routing: Secure Routing for Mixnets

Anonymous communication networks are important building blocks for online privacy protection. One approach to achieve anonymity is to relay messages through multiple routers, where each router shuffles messages independently. To achieve anonymity, at least one router needs to be honest. In the presence of an adversary that is controlling a subset of the routers unbiased routing is important for guaranteeing anonymity. However, the routing strategy also influenced other factors such as the scalability and the performance of the system. One solution is to use a fixed route for relaying all messages with many routers. If the route is not fixed the routing decision can either be made by the communication initiator or the intermediate routers. However, the existing routing types each have limitations. For example, one faces scalability issues when increasing the throughput of systems with fixed routes. Moreover, when the routing decision is left to the initiator, the initiator needs to maintain an up-to-date view of the system at all times, which also does not scale. If the routing decision is left to intermediate routers the routing of the communication can be influenced by an adversary. In this work, we propose a novel multiparty routing approach for anonymous communication that addresses these shortcomings. We distribute the routing decision and verify the correctness of routing to achieve routing integrity. More concretely, we provide a mixnet design that uses our routing approach and that in addition, addresses load balancing. We show that our system is secure against a global active adversary.

cs.CR↗