Gaetano Russo

Digital signatures are a critical cryptographic primitive requiring quantum-safe solutions. One possibility are quantum digital signatures (QDS), which offer information-theoretic (IT) security without a trusted authority. However, even the most promising QDS proposals are largely limited to the tripartite scenario (one sender, two receivers) and are vulnerable to equivocation-based attacks that hinder transferability and non-repudiation. To overcome such limitations, we introduce an equivocation-resistant signature (ERS) protocol based on preshared keys and universal hashing that achieves IT security and scales to an arbitrary number of receivers. We benchmark the ERS protocol against state-of-the-art QDS schemes demonstrating orders-of-magnitude reductions in preshared key consumption and signature size. Our findings position our ERS protocol as a strong candidate for implementing IT-secure digital signatures in today’s quantum communication infrastructures.

We investigate three promising Quantum Digital Signature (QDS) protocols that can sign arbitrarily long documents with information-theoretic security. We re-derive the security proof of each scheme obtaining, where possible, tighter security bounds while closing security loopholes caused by using non-authenticated communication. In one case, we upgrade the QDS protocol to information-theoretic security by replacing NIST-recommended hash functions with universal hashing. We systematically compare the performance of the three protocols by optimizing over their parameters and deduce the protocol requiring the shortest signatures and the minimal number of preshared secret bits. Finally, we propose a multi-partite QDS protocol that retains the best features of the analyzed protocols while allowing for an arbitrary number of receivers.