Abstract Realistic quantum key distribution (QKD) systems suffer from side-channel attacks, which manipulate single-photon detectors. Although measurement-device-independent QKD schemes were proposed to free QKD parties (Alice and Bob) from such measurement devices, these schemes are not easy to be implemented in practice because they require precise synchronization between signals from distant parties. On the other hand, differential phase shift (DPS) QKD is a simple system for practical implementation with current optical equipment. In this study, we propose a simple modification in DPS QKD to prevent side-channel attacks (control blinding and controlling attacks) such that Bob randomly attenuates the incoming signal. This modification allows Bob to utilize photon statistics during attenuated time slots in DPS-QKD systems, using which the side-channel attacks are revealed.
Abstract Side-channel attacks manipulating single-photon detectors (SPDs) have known to be loopholes in realistic quantum key distribution (QKD) systems. Although measurement-device-independent (MDI) QKD schemes have been proposed and studied to avoid those loopholes, they are not easy to implement in practice because they Require some synchronization between signals sent from two distant parties. In this paper, we propose a new countermeasure against a side-channel attack (control blinding and controlling attacks). It utilizes coincident clicks in differential-quadrature-phase shift (DQPS) QKD systems. Our scheme requires no change in the system configuration of the conventional protocol. Unlike MDI-QKD, side-channel attacks can be found without difficulty in practical implementations.
This paper proposes a measurement-device-independent quantum key distribution (MDI-QKD) scheme based on differential phase encoding. The differential phase shift MDI-QKD (DPS-MDI-QKD) couples the advantages of DPS-QKD with that of MDI-QKD. The proposed scheme offers resistance against photon number splitting attack and phase fluctuations as well as immunity against detector side-channel vulnerabilities. The design proposed in this paper uses weak coherent pulses in a superposition of three orthogonal states, corresponding to one of three distinct paths in a delay-line interferometer. The classical bit information is encoded in the phase difference between pulses traversing successive paths. This 3-pulse superposition offers enhanced security compared to using a train of pulses by decreasing the learning rate of an eavesdropper and unmasking her presence with an increased error rate upon application of intercept and resend attack and beamsplitter attack. The proposed scheme employs phase locking of the sources of the two trusted parties so as to maintain the coherence between their optical signal, and uses a beamsplitter (BS) at the untrusted node (Charlie) to extract the key information from the phase encoded signals.
In quantum key distribution (QKD), eavesdropping is generally detected based on bit errors resulting from eavesdropper attacks. This study proposes a QKD scheme for detecting eavesdropping based on the photon-detection rate instead of the bit error rate. The differential-phase-shift (DPS) QKD protocol, which transmits lasting weak coherent pulses, is modified such that decoy pulses with a large mean photon number are randomly inserted into a signal pulse sequence. With this modification, eavesdropping can be detected by monitoring the photon-detection rates at the time slots around the decoy pulses. The key-creation performance of the modified DPS-QKD system is evaluated, and the results indicate that the QKD distance is increased with the modification.
In May 2014, a new quantum key distribution protocol named “Round Robin Differential-Phase-Shift Quantum Key
Distribution (RR DPS QKD)” was proposed. It has a special feature that the key consumption via privacy amplification is
a small constant because RR DPS QKD guarantees its security by information causality, not by information-disturbance
trade-off. Therefore, the authors claimed that RR DPS QKD systems does not need to monitor the disturbance by an
attacker in the quantum channel. However, this study shows that a modified Faked-State Attack (or so-called bright
illumination attack) can hack a RR DPS QKD system almost perfectly if it is implemented with realistic detectors even
information-causality guarantees the security of RR DPS QKD protocol. Therefore, this study also proposes a possible
Measurement-Device-Independent RR DPS QKD system to avoid the modified Faked-State Attack.
The differential-phase-shift (DPS) quantum-key-distribution (QKD) protocol was proposed aiming at simple implementation, but it can tolerate only a small disturbance in a quantum channel. The round-robin DPS (RRDPS) protocol could be a good solution for this problem, which in fact can tolerate even up to
50 of a bit error rate. Unfortunately, however, such a high tolerance can be achieved only when we compromise the simplicity, i.e., Bob's measurement must involve a large number of random delays (
∣R∣ denotes its number), and in a practical regime of
∣R∣ being small, the tolerance is low. In this paper, we propose a DPS protocol to achieve a higher tolerance than the one in the original DPS protocol, in which the measurement setup is less demanding than the one of the RRDPS protocol for the high tolerance regime. We call our protocol the small-number-random DPS (SNRDPS) protocol, and in this protocol, we add only a small amount of randomness to the original DPS protocol, i.e., $2\ensuremath{\le}|\mathcal{R}|\ensuremath{\le}10$. In fact, we found that the performance of the SNRDPS protocol is significantly enhanced over the original DPS protocol only by employing a few additional delays such as
∣R∣=2. Also, we found that the key generation rate of the SNRDPS protocol outperforms the RRDPS protocol without monitoring the bit error rate when it is less than
5 and $|\mathcal{R}|\ensuremath{\le}10$. Our protocol is an intermediate protocol between the original DPS protocol and the RRDPS protocol, and it increases the variety of the DPS-type protocols with quantified security.