Improving Classical Authentication with Quantum Communication

We propose a quantum-enhanced protocol to authenticate classical messages, with improved security with respect to the classical scheme introduced by Brassard in 1983. In that protocol, the shared key is the seed of a pseudo-random generator (PRG) and a hash function is used to create the authentication tag of a public message. We show that a quantum encoding of secret bits offers more security than the classical XOR function introduced by Brassard. Furthermore, we establish the relationship between the bias of a PRG and the amount of information about the key that the attacker can retrieve from a block of authenticated messages. Finally, we prove that quantum resources can improve both the secrecy of the key generated by the PRG and the secrecy of the tag obtained with a hidden hash function.