A Quantum Dialogue Protocol Based on Four-Qubit Entangled State

A quantum dialogue protocol is proposed based on four-qubit entangled state, which is constructed by an EPR pair and two different single qubits through three controlled-not gates. By using Bell measurements and the corresponding unitary operation, two users can exchange their messages simultaneously and directly without sharing any secret keys beforehand. Security analysis shows that this protocol can resist the-intercept-resend attack and the entanglement-measure attack. The protocol is simple and feasible with current technique.