Jialei Su

High-speed quantum key distribution (QKD) systems have achieved repetition frequencies above gigahertz through advanced technologies and devices, laying an important foundation for the deployment of high-key-rate QKD system. However, these advancements may introduce unknown security loopholes into the QKD system. For an eavesdropper Eve, it is challenging to exploit these security loopholes performing the intercept-and-resend attacks due to the limited time window under the high repetition frequency. Here, we propose a muted attack that does not require intercept-and-resend operation, which is applicable to high-speed QKD systems. By exploiting the security loophole of the width discriminator on the single photon avalanche detector (SPAD), Eve can control whether Bob’s detector is capable of receiving photons from Alice, allowing her to learn nearly all the keys. Additionally, we verified through experimental tests that Eve only needs to match the period of the hacking pulse with the dead time of the SPAD and ensure that each pulse contains hundreds of photons. This study reveals the security loopholes introduced by the state-of-the-art devices in high-speed QKD systems.