Secret key rates for coherent attacks

TL;DR

This paper introduces a new method to compute secret key rates for quantum key distribution protocols under coherent attacks, simplifying the problem by relating it to collective attacks and showing its effectiveness on BB84 and six-state protocols.

Contribution

The paper presents a novel approach to bound secret key rates for permutation-invariant protocols under coherent attacks by reducing the problem to collective attacks analysis.

Findings

Method effectively bounds secret key rates for coherent attacks.

Comparison shows high relevance to existing post-selection techniques.

Progress in collective attack analysis benefits this method.

Abstract

We develop a new method to quantify the secret key rate for permutation-invariant protocols for coherent attacks and finite resources. The method reduces the calculation of secret key rates for coherent attacks to the calculation for collective attacks by bounding the smooth min-entropy of permutation-invariant states via the smooth min-entropy of corresponding tensor-product states. The comparison of the results to the well-known post-selection technique for the BB84 and six-state protocol shows the high relevance of this method. Since our calculation of secret key rates for coherent attacks strongly depends on the way of treating collective attacks, a prospective progress in the analysis of collective attacks will immediately cause progress in our strategy.