The security proofs of the Quantum Key Distribution (QKD) protocols make certain assumptions about the operations of physical systems. Thus, appropriate modelling of devices to ensure that their operations are consistent with the models assumed in the security proof is imperative. In this paper, we explore the Trojan horse attack (THA) using Measurement Device Independent (MDI) QKD integrated photonic chips and how to avoid some of the security vulnerabilities using only on-chip components. We show that a monitor photodiode paired appropriately with enough optical isolation, given the sensitivity of the photodiode, can detect high power sniffing attacks. We also show that the placement of amplitude modulators with respect to back reflecting components and their switching time can be used to thwart a THA.
The security proofs of the Quantum Key Distribution (QKD) protocols make certain assumptions about the operations of physical systems. Thus, appropriate modelling of devices to ensure that their operations are consistent with the models assumed in the security proof is imperative. In this paper, we explore the Trojan horse attack (THA) using Measurement Device Independent (MDI) QKD integrated photonic chips and how to avoid some of the security vulnerabilities using only on-chip components. We show that a monitor photodiode paired appropriately with enough optical isolation, given the sensitivity of the photodiode, can detect high power sniffing attacks. We also show that the placement of amplitude modulators with respect to back reflecting components and their switching time can be used to thwart a THA.
Silicon photonics offers a stable, miniaturized platform for quantum key distribution (QKD). As such, the chip-based system is vital for a wider adoption of QKD in the near future. However, the practical security issues presented in this alternative platform have not been fully studied. Here, we theoretically and experimentally evaluate the security of a chip-based QKD system under a powerful source attack, namely, Trojan-horse attack. We analyze the finite-key security of two prominent QKD protocols---BB84 and measurement-device-independent QKD---with the information leakage from both the polarization modulator and the intensity modulator integrated on a silicon photonic chip. Furthermore, we prove that our chip-based measurement-device-independent QKD system is feasibly resistant to the Trojan-horse attack by adding 232-dB isolation to the chip. In this sense, our work provides a guideline for the secure implementation of a leaky transmitter chip in the QKD system.
Abstract Most security proofs of quantum key distribution (QKD) disregard the effect of information leakage from the users’ devices, and, thus, do not protect against Trojan-horse attacks (THAs). In a THA, the eavesdropper injects strong light into the QKD apparatuses, and then analyzes the back-reflected light to learn information about their internal setting choices. Only a few recent works consider this security threat, but predict a rather poor performance of QKD unless the devices are strongly isolated from the channel. Here, we derive finite-key security bounds for decoy-state-based QKD schemes in the presence of THAs, which significantly outperform previous analyses. Our results constitute an important step forward to closing the existing gap between theory and practice in QKD.
Measurement-device-independent quantum key distribution (MDI QKD) is a promising method for remote key sharing that can eliminate all detector side-channel attacks. However, current security proofs often overlook the potential information leakages from the legitimate users' devices. In a quantum version of Trojan-horse attack (THA), a malicious eavesdropper can inject bright light into the sources of a MDI QKD system and then analyze the back-reflected light to obtain their setting choices, thereby compromising the final security. Here, we derive the finite-key security bounds of decoy-state MDI QKD in the presence of THA, which significantly outperform previous analyses in terms of the secret-key rate and transmission distance. Specifically, we analyze a symmetric three-intensity decoy-state MDI QKD protocol and an efficient four-intensity decoy-state MDI QKD protocol. Our results represent a fundamental step in guaranteeing the implementation security of quantum communication systems.
Reference-frame-independent measurement-device-independent quantum key distribution (RFI MDI QKD) can resist side-channel attacks against detectors and slow variations of reference frames, thus presenting an advantageous approach for long-distance secure quantum communication. Nevertheless, if an eavesdropper implements a Trojan-horse attack (THA) by injecting bright light into sources, the back-reflected light may carry encoding information into the channel, thereby causing serious information leakage. In this paper, we theoretically evaluate the finite-key security of decoy-state RFI MDI QKD against a THA by employing the reference-state technique and a particular concentration inequality. Additionally, dual-parameter optimization and multibasis-estimation strategies are introduced to reduce statistical fluctuations effectively. Our work demonstrates that RFI MDI QKD can maintain a better performance even in the presence of large reference-frame drifts and a THA, representing a key advancement in strengthening the security of quantum communication in real-world implementations.
Quantum key distribution (QKD), which theoretically provides unconditional secure communication, has developed rapidly in the past decades. However, the practical QKD systems still have vulnerabilities due to device imperfections. Polarization-encoding systems are one of the most important branches in the field of QKD. To date, a variety of polarization-encoding schemes have been proposed to meet the requirements of high speed and robust modulation, but the security analysis of these schemes is often ignored. In this paper, we experimentally and theoretically evaluated the security of three typical polarization encoders against the Trojan horse attack (THA), which is recognized as one of the critical quantum attacks. We built a system to implement the THA and collected the reflection from QKD configuration with different encoders. According to the experimental results, we further analyzed the secure key rate and the resistance against THAs of the system while BB84 or measurement-device-independent QKD was applied. Our paper plays an important guiding role in the design of polarization encoders and the construction of secure QKD systems with realistic devices.
Quantum key distribution (QKD) leverages the principles of quantum mechanics to exchange a secret key between two parties. Unlike classical cryptographic systems, the security of QKD is not reliant on computational assumptions but is instead rooted in the fundamental laws of physics. In a QKD protocol, any attempt by an eavesdropper to intercept the key is detectable: this provides an unprecedented level of security, making QKD an attractive solution for secure communication in an era increasingly threatened by the advent of quantum computers and their potential to break classical cryptographic systems. However, QKD also faces several practical challenges such as transmission loss and noise in quantum channels, finite key size effects, and implementation flaws in QKD devices. Addressing these issues is crucial for the large-scale deployment of QKD and the realization of a global quantum Internet. A whole body of research is dedicated to the hacking of the quantum state source, for example using (THAs), where the eavesdropper injects light into the system and analyzes the back-reflected signal. In this paper, we study the vulnerabilities against THAs of the iPOGNAC encoder, first introduced in [M. Avesani , ], to propose adapted countermeasures that can mitigate such attacks.