Advantage of the key relay protocol over secure network coding

TL;DR

This paper compares the key relay protocol (KRP) and secure network coding (SNC), revealing that KRPs can offer superior security, and that their differences can be bridged by adding free public channels to SNC.

Contribution

The paper rigorously analyzes the security differences between KRP and SNC, showing KRPs outperform SNC in certain cases and establishing their equivalence with augmented SNC schemes.

Findings

KRPs achieve better security than SNC on the same graph.

Adding free public channels to SNC makes it equivalent to KRP.

A gap in security exists between traditional KRP and SNC schemes.

Abstract

The key relay protocol (KRP) plays an important role in improving the performance and the security of quantum key distribution (QKD) networks. On the other hand, there is also an existing research field called secure network coding (SNC), which has similar goal and structure. We here analyze differences and similarities between the KRP and SNC rigorously. We found, rather surprisingly, that there is a definite gap in security between the KRP and SNC; that is, certain KRPs achieve better security than any SNC schemes on the same graph. We also found that this gap can be closed if we generalize the notion of SNC by adding free public channels; that is, KRPs are equivalent to SNC schemes augmented with free public channels.