Two-way deterministic quantum key distribution against passive detector side channel attacks in the forward line
In the four-state two-way deterministic quantum key distribution (DQKD) protocol, Bob prepares a qubit randomly in one of four states and sends it to Alice. Alice encodes her key bit on the arrival qubit and returns it to Bob who measures the redux qubit to decode Alices key bit in a deterministic manner, without basis reconciliation. The unconditional security of the final key of this protocol has been proven in the ideal-device settings. Recently, it has been proven that two-way DQKD protocol is immune to all detector side channel attacks in the backward line A-to-B. In this paper, we study the security of two-way DQKD against passive detector side channel attacks in the forward line B-to-A. In a passive detector side channel attack, the eavesdropper Eve does not disturb quantum state of travel photon but utilizes the efficiency mismatch of two single-photon detectors to estimate the value of key bits, such as the time-shift attack. We prove that two-way DQKD is immune against all passive detector side channel attacks in the forward line B-to-A, although such attacks are efficient on BB84 protocol.
two-way detector side channel attack quantum communication