Improving the key rate of decoy state-based QKD scheme using self-healing technique

Abstract

In any QKD scheme, a train of encoded laser pulses is shared between legitimate users as a raw key. The actual key is extracted from the raw key by eliminating eavesdropping and other loss factors in the communication channel. Several pulses are used in error estimation and correction, resulting in a low key generation rate. It can be improved by reducing losses in the communication channel and the probability of eavesdropping. That can effectively be done by reducing the amount of physical communication. The self-healing technique of physical communication at alternate time intervals and no communication in between is proposed and implemented in the decoy-state-based quantum key distribution (QKD) protocol. Legitimate users can generate the uncommunicated state from the pre- and post-communicated states. Since physical communication is reduced by half, loss of the signal states in the channel and eavesdropping are reduced; it is analyzed and assessed. Security analysis reveals that the key generation rate and the length of secure communication are improved. Data encryption is done through phase-encoded weak coherent laser pulses. In the proposed protocol, legitimate users use a pre-shared one-way function to select bases and intensities of the signal states. Both participate in setting the argument of the one-way function. It ensures user authentication, and no separate authentication protocol is required. This, in turn, eliminates the man-in-the-middle attack.

The one-way function ensures a basis correlation between the subsequent pulses and, to some extent, intensity correlation. It helps legitimate users encode and decode the signal and reduces measurement uncertainty. But, the one-way function being unknown to Eve, the signal states are random to her. So, her measurement is subject to quantum uncertainty. The self-healing technique further complicates the situation as Eve has no access to the uncommunicated pulses. From that point of view, the data leakage to Eve is less. However, Eve’s intervention may create little loss of signal states. The proposed self-healing technique allows for its complete identification and assessment. An error bound corresponding to it is determined, and the key generation rate is calculated.