An attack aimed at active phase compensation in one-way phase-encoded QKD systems

Phase drift is an inherent problem in one-way phase-encoded quantum key distribution (QKD) systems. Although combining passive with active phase compensation (APC) processes can effectively compensate for the phase drift, the security problems brought about by these processes are rarely considered. In this paper, we point out a security hole in the APC process and put forward a corresponding attack scheme. Under our proposed attack, the quantum bit error rate (QBER) of the QKD can be close to zero for some conditions. However, under the same conditions the ratio r of the key 0 and the key 1 which Bob (the legal communicators Alice and Bob) gets is no longer 1:1 but 2:1, which may expose Eve (the eavesdropper). In order to solve this problem, we modify the resend strategy of the attack scheme, which can force r to reach 1 and the QBER to be lower than the tolerable QBER.