Quantum key distribution with delayed privacy amplification and its application to security proof of a two-way deterministic protocol

TL;DR

This paper demonstrates that delaying privacy amplification in quantum key distribution does not compromise security or key rate, simplifying security proofs and enabling new applications like two-way deterministic protocols.

Contribution

It introduces the concept of delayed privacy amplification in QKD, proving its security and applying it to simplify security proofs of two-way protocols.

Findings

Security and key rate unaffected by delaying PA

Simplifies security proof of two-way QKD protocols

Proves security of a specific two-way deterministic protocol

Abstract

Privacy amplification (PA) is an essential post-processing step in quantum key distribution (QKD) for removing any information an eavesdropper may have on the final secret key. In this paper, we consider delaying PA of the final key after its use in one-time pad encryption and prove its security. We prove that the security and the key generation rate are not affected by delaying PA. Delaying PA has two applications: it serves as a tool for significantly simplifying the security proof of QKD with a two-way quantum channel, and also it is useful in QKD networks with trusted relays. To illustrate the power of the delayed PA idea, we use it to prove the security of a qubit-based two-way deterministic QKD protocol which uses four states and four encoding operations.