arXiv subjects

Ahto Buldas

Publications and source records attributed to Ahto Buldas.

4 recordsLinked to original sources

arXiv2026

The Trust-Free Aggregation Layer of the Unicity Infrastructure

Unicity is a novel blockchain infrastructure for enabling users to execute off-chain peer-to-peer token transactions while preventing parallel states of tokens (double-spending) with minimal blockchain complexity and storage. A key component of the infrastructure is the Aggregation Layer responsible for storing information about the spent states of tokens and providing compact cryptographic proofs of no double-spending for the users without making any compromises in trust. Aggregation Layer is a layer 2 style service that holds an append-only key-value repository that periodically certifies its state using a traditional blockchain that we call the Consensus Layer. Every time while certifying a changed state the Aggregation Layer provides a cryptographic proof to the Consensus Layer about the append-only consistency of the key-value store. We use the Radix Sparse Merkle Trees (RSMTs) to create the cryptographic digest r_i of the store in every round i and authentication paths of special type in order to prove that the next digest r_{i+1} was obtained while only adding some key-value pairs (k,v) to the repository. The proof verification code is implemented as an Algebraic Intermediate Representation (AIR) circuit on top of the Plonky3 STARK toolkit. Our implementation uses no trusted setup, achieves throughput of 10,000 insertions per second and and millisecond range verification time on a single consumer-class CPU.

cs.CR↗

arXiv2026

The Unicity Execution Layer

This paper introduces the Unicity Execution Layer, a modular component of the Unicity framework enabling secure off-chain transactions while maintaining trustless double-spending prevention. We present a formal security model where token ownership is represented by public keys and transfers require digital signatures. We prove three fundamental security properties: (1) no double-spending--each token state can be spent at most once, (2) no blocking--only the legitimate owner can prevent a token from being spent, and (3) service-side privacy--the Unicity Service cannot link transactions with the same token. The user-side privacy is addressed by introducing generalized multi-public-key signature schemes that allow one secret to generate multiple unlinkable public keys, and interactive and non-interactive concrete instantiations, enabling private transactions with stable public identity with minimal key management overhead.

cs.CR↗

arXiv2026

Unicity: Predicates and Atomic Swaps

We generalize Unicity token ownership to programmable spending conditions called predicates, enabling smart-contract like functionality executed off-chain directly by relying parties rather than by consensus participants. We prove that the security properties of the Unicity execution layer are preserved under reduction to predicate family unforgeability. To demonstrate the utility of the model, we show how to implement trustless atomic swaps by using predicates.

cs.CR↗

arXiv2019

Attribute Evaluation on Attack Trees with Incomplete Information

Attack trees are considered a useful tool for security modelling because they support qualitative as well as quantitative analysis. The quantitative approach is based on values associated to each node in the tree, expressing, for instance, the minimal cost or probability of an attack. Current quantitative methods for attack trees allow the analyst to, based on an initial assignment of values to the leaf nodes, derive the values of the higher nodes in the tree. In practice, however, it shows to be very difficult to obtain reliable values for all leaf nodes. The main reasons are that data is only available for some of the nodes, that data is available for intermediate nodes rather than for the leaf nodes, or even that the available data is inconsistent. We address these problems by developing a generalisation of the standard bottom-up calculation method in three ways. First, we allow initial attributions of non-leaf nodes. Second, we admit additional relations between attack steps beyond those provided by the underlying attack tree semantics. Third, we support the calculation of an approximative solution in case of inconsistencies. We illustrate our method, which is based on constraint programming, by a comprehensive case study.

cs.CR↗