Simulation of quantum key expansion using quantum cellular automata

Quantum cryptography has become reality nowadays and quantum key distribution systems are already in use. In classical cryptography, key expansion schemes are used to strengthen security. In this paper we present a quantum key expansion scheme, in which the key is expanded using a quantum cellular automaton. We also present the simulation of quantum key expansion using a quantum computer simulator. Using this scheme a 6-qubit key transmitted from the sender to the receiver, using one of the quantum key distribution protocols, can be expanded to a 24-qubit key without any further communication between them.