Continuous-Variable Quantum Key Distribution with Entanglement in the Middle

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.