  In order to avoid the risk of information leakage during the information
mutual transmission between two authorized participants, i.e., Alice and Bob, a
quantum dialogue protocol based on the entanglement swapping between any two
Bell states and the shared secret Bell state is proposed. The proposed protocol
integrates the ideas of block transmission, two-step transmission and unitary
operation encoding together using the Bell states as the information carriers.
Besides the entanglement swapping between any two Bell states, a shared secret
Bell state is also used to overcome the information leakage problem, which not
only makes Bob aware of the prepared initial state but also is used for Bob's
encoding and entanglement swapping. Security analysis shows that the proposed
protocol can resist the general active attacks from an outside eavesdropper
Eve. Moreover, the relation between the maximal amount of information Eve can
gain and the detection probability is derived.
