A “Ping-pong” Protocol with Authentication

The quantum secure direct communication is a new-style quantum communication scheme. It arouses much interest recently. The ping-pong protocol proposed by Bostroem and Felbinger is one of relatively mature quantum secure direct communication protocols, which is asymptotically secure under Eve´s eavesdropping attack. But it ignores the message authentication. Being aimed at this problem, we propose a novel ping-pong protocol with authentication. The former has two operation modes, or the message mode and the control mode, which are used to send message and detect Eve´s attack, respectively. But it just detects Eve´s eavesdropping attack and does not authenticate the sent message in the control mode. The latter has also the above two operation modes, which employs a braid-based key agreement protocol for both the parties participating in communication to share a secret, whose size and magnitude are undecided in advance. Using the shared secret, it not only detects Eve´s eavesdropping attack, but also effectively performs the message authentication in the control mode. It is also asymptotically secure under Eve´s eavesdropping attack. The security of the proposed protocol is based on the no-cloning theorem, the correlations of quantum entanglement and the fact that the p-th root finding problem on braid groups is intractable even on quantum computers, as well as classical computers. In addition different from the original ping-pong protocol, the communication was initiated by the sender Alice instead of by the receiver Bob. This corresponds to the way of common communications. The present protocol not only can resist the attacks known recently, but should be experimentally feasible using today´s technology.