Symmetric collective attacks for the eavesdropping of symmetric quantum key distribution

TL;DR

This paper analyzes symmetric collective eavesdropping attacks on BB84 and six-state quantum key distribution protocols, demonstrating their strength in minimizing secure key rates and providing simple examples reaching optimal security bounds.

Contribution

It introduces symmetric collective attack models tailored to symmetric QKD protocols, showing their effectiveness in reducing key rates and achieving unconditional security limits.

Findings

Symmetric collective attacks can minimize Devetak-Winter key rates.

Simple attack examples can reach unconditionally-secure key rates.

Symmetry in attacks aligns with protocol symmetry to enhance eavesdropping effectiveness.

Abstract

We consider the collective eavesdropping of the BB84 and six-state protocols. Since these protocols are symmetric in the eigenstates of conjugate bases, we consider collective attacks having the same kind of symmetry. We then show how these symmetric collective attacks are sufficiently strong in order to minimize the Devetak-Winter rates. In fact, it is quite easy to construct simple examples able to reach the unconditionally-secure key-rates of these protocols.