Security of Partially Corrupted Repeater Chains

TL;DR

This paper analyzes the security of quantum key distribution over repeater chains when the adversary can only corrupt a contiguous segment, leading to improved security and noise tolerance in large-scale quantum networks.

Contribution

It provides a rigorous finite key security proof for quantum networks with partial adversarial control, a scenario less explored in prior work.

Findings

Security is achievable with partial adversary control in repeater chains.

Enhanced noise tolerance is possible under the partial corruption model.

Finite key security bounds are derived for this scenario.

Abstract

Quantum Key Distribution allows two parties to establish a secret key that is secure against computationally unbounded adversaries. To extend the distance between parties, quantum networks, and in particular repeater chains, are vital. Typically, security in such scenarios assumes the absolute worst case: namely, an adversary has complete control over all repeaters and fiber links in a network and is able to replace them with perfect devices, thus allowing her to hide her attack within the expected natural noise. In a large-scale network, however, such a powerful attack may be infeasible. In this paper, we analyze the case where the adversary can only corrupt a contiguous subset of a repeater chain connecting Alice and Bob, while some portion of the network near Alice and Bob may be considered safe from attack (though still noisy). We derive a rigorous finite key proof of security assuming this attack model and show that improved performance and noise tolerances are possible.