  In this paper, two fault tolerant channel-encrypting quantum dialogue (QD)
protocols against collective noise are presented. One is against
collective-dephasing noise, while the other is against collective-rotation
noise. The decoherent-free states, each of which is composed of two physical
qubits, act as traveling states combating collective noise.
Einstein-Podolsky-Rosen pairs, which play the role of private quantum key, are
securely shared between two participants over a collective-noise channel in
advance. Through encryption and decryption with private quantum key, the
initial state of each traveling two-photon logical qubit is privately shared
between two participants. Due to quantum encryption sharing of the initial
state of each traveling logical qubit, the issue of information leakage is
overcome. The private quantum key can be repeatedly used after rotation as long
as the rotation angle is properly chosen, making quantum resource economized.
As a result, their information-theoretical efficiency is nearly up to 66.7%.
The proposed QD protocols only need single-photon measurements rather than
two-photon joint measurements for quantum measurements. Security analysis shows
that an eavesdropper cannot obtain anything useful about secret messages during
the dialogue process without being discovered. Furthermore, the proposed QD
protocols can be implemented with current techniques in experiment.
