# Continuous-variable quantum digital signatures over insecure channels

## TL;DR

This paper introduces a continuous-variable quantum digital signature scheme that remains secure even with eavesdroppers, enabling practical implementation alongside existing quantum key distribution systems.

## Contribution

The paper presents the first CV QDS scheme secure against eavesdroppers, using phase measurement of coherent states, with shorter signatures than previous protocols.

## Key findings

- Secure against collective beamsplitter and entangling-cloner attacks
- Allows eavesdropper presence with shorter signatures
- Compatible with existing CV QKD platforms

## Abstract

Digital signatures ensure the integrity of a classical message and the authenticity of its sender. Despite their far-reaching use in modern communication, currently used signature schemes rely on computational assumptions and will be rendered insecure by a quantum computer. We present a quantum digital signatures (QDS) scheme whose security is instead based on the impossibility of perfectly and deterministically distinguishing between quantum states. Our continuous-variable (CV) scheme relies on phase measurement of a distributed alphabet of coherent states, and allows for secure message authentication against a quantum adversary performing collective beamsplitter and entangling-cloner attacks. Crucially, for the first time in the CV setting we allow for an eavesdropper on the quantum channels and yet retain shorter signature lengths than previous protocols with no eavesdropper. This opens up the possibility to implement CV QDS alongside existing CV quantum key distribution (QKD) platforms with minimal modification.