Secure and practical Quantum Digital Signatures

Digital signatures represent a crucial cryptographic asset that must be protected against quantum adversaries. Quantum Digital Signatures (QDS) can offer solutions that are information-theoretically (IT) secure and thus immune to quantum attacks. In this work, we analyze three existing practical QDS protocols based on preshared secure keys (e.g., established with quantum key distribution) and universal hashing families. For each protocol, we make amendments to close potential loopholes and prove their IT security while accounting for the failure of IT-secure authenticated communication. We then numerically optimize the protocol parameters to improve efficiency in terms of preshared bit consumption and signature length, allowing us to identify the most efficient protocol.