Continuous-Variable Quantum Key Distribution with Entanglement in the Middle

TL;DR

This paper investigates continuous-variable quantum key distribution where the entangled source is untrusted and potentially malicious, demonstrating that secure key generation is still possible without trusting the source.

Contribution

It introduces a method to securely perform quantum key distribution with an untrusted source located between the communicating parties, expanding the security model.

Findings

Positive key rate achievable with untrusted middle source

Source trust not necessary for secure key generation

Applicable to quantum networks with untrusted intermediaries

Abstract

We analyze the performance of continuous-variable quantum key distribution protocols where the entangled source originates not from one of the trusted parties, Alice or Bob, but from the malicious eavesdropper in the middle. This is in contrast to the typical simulations where Alice creates the entangled source and sends it over an insecure quantum channel to Bob. By using previous techniques and identifying certain error correction protocol equivalences, we show that Alice and Bob do not need to trust their source, and can still generate a positive key rate. Such a situation can occur in a quantum network where the untrusted source originated in between the two users.