Quantum Coin-Flipping-Based Authentication

Quantum cryptographic key distribution (QKD) is a promising candidate for achieving unconditional security, making the renowned one-time pad encryption technically feasible for building computer networks. However, although well-developed theoretical foundations perfectly ensure protection against eavesdropping, no natural mechanism is yet able to successfully repel an adversary sitting between Alice and Bob, performing QKD with both and re-encrypting each message after heaving read it in plain text. Authentication is hence of crucial importance, and normally applied to all messages that are related to the public discussion part of the QKD protocol. We present an analysis of a scenario, in which authentication is postponed until the end of the QKD protocol. This yields to reduced computational effort, as well as simple and tight bounds on the amount of pre-shared key material. Our solution relies on a combination of quantum key distribution and quantum coin-flipping, which ensures non- controllability of the QKD key. Based on this assumption, we can apply a standard fingerprint comparison for authentication, to guard the protocol against a person-in-the-middle attack.