Authenticated B92 QKD protocol employing synchronized optical chaotic systems

Quantum key distribution (QKD) is not secure without an authentication protocol running together. The aim of the authentication protocol is to guarantees the identity of legitimate users, avoiding the man-in-the-middle attack. An authentication protocol requires an initially shared secret and it can be realized by software or by a physical system. In the first case a pseudo-random number generator (PRNG) is used while in the second case synchronized optical chaotic systems can be employed. In this direction, the present work considers both cases. Firstly, we show how to implement an authenticated polarization-based B92 QKD protocol using a PRNG. Its security is analyzed taking into account the number of bits of the pre-shared secret. Following, we describe a chaos-based authenticated B92 QKD protocol: We consider a chaotic system whose output is a light polarization state that changes chaotically and the synchronization of two of such systems. The Stokes' parameter S-1 of the output field is used to obtain a pseudo-random bit sequence that is used to implement the authentication. We emphasize functional limits for these two implementations.