Integrated continuous-variable quantum key distribution (CV-QKD) systems based on photonic chips offer a promising avenue for establishing large-scale and low-cost global quantum networks. In such systems, the grating coupler (GC) serves as an interface for optical coupling, but its strongly wavelength-dependent efficiency creates a severe security loophole in practice. In this paper, we propose a wavelength-shifting attack targeting the wavelength-dependent GC in chip-based CV-QKD systems. By intercepting Alice’s quantum states and resending forged quantum states together with a local oscillator (LO), both at a shifted wavelength, this attack manipulates the receiver’s excess-noise estimation, effectively masking the excess noise introduced by Eve. Numerical simulations show that the attack can keep Bob’s estimated excess noise below the security threshold, leading Alice and Bob to infer a positive secret key rate while the actual secure key rate is zero. This research reveals how the integrated components can be exploited to mount side-channel attacks. To mitigate this vulnerability, we propose practical defenses, including on-chip wavelength monitoring and randomized shot-noise calibration. These findings provide important guidance for the secure development of next-generation integrated quantum communication systems.
Integrated continuous-variable quantum key distribution (CV-QKD) systems based on photonic chips offer a promising avenue for establishing large-scale and low-cost global quantum networks. In such systems, the grating coupler (GC) serves as an interface for optical coupling, but its strongly wavelength-dependent efficiency creates a severe security loophole in practice. In this paper, we propose a wavelength-shifting attack targeting the wavelength-dependent GC in chip-based CV-QKD systems. By intercepting Alice’s quantum states and resending forged quantum states together with a local oscillator (LO), both at a shifted wavelength, this attack manipulates the receiver’s excess-noise estimation, effectively masking the excess noise introduced by Eve. Numerical simulations show that the attack can keep Bob’s estimated excess noise below the security threshold, leading Alice and Bob to infer a positive secret key rate while the actual secure key rate is zero. This research reveals how the integrated components can be exploited to mount side-channel attacks. To mitigate this vulnerability, we propose practical defenses, including on-chip wavelength monitoring and randomized shot-noise calibration. These findings provide important guidance for the secure development of next-generation integrated quantum communication systems.
The wavelength attack utilizes the dependence of beam splitters (BSs) on wavelength to cause legitimate users Alice and Bob to underestimate their excess noise so that Eve can steal more secret keys without being detected. Recently, the wavelength attack on Gaussian-modulated continuous-variable quantum key distribution (CV-QKD) has been researched in both fiber and atmospheric channels. However, the wavelength attack may also pose a threat to the case of ocean turbulent channels, which are vital for the secure communication of both ocean sensor networks and submarines. In this work, we propose two wavelength attack schemes on underwater discrete modulated (DM) CV-QKD protocol, which is effective for the case with and without local oscillator (LO) intensity monitor, respectively. In terms of the transmittance properties of the fused biconical taper (FBT) BS, two sets of wavelengths are determined for Eve's pulse manipulation, which are all located in the so-called blue-green band. The derived successful criterion shows that both attack schemes can control the estimated excess noise of Alice and Bob close to zero by selecting the corresponding condition parameters based on channel transmittance. Additionally, our numerical analysis shows that Eve can steal more bits when the wavelength attack controls the value of the estimated excess noise closer to zero.
Quantum key distribution (QKD) is a quantum communication technology that offers absolute security. Among its various implementations, continuous-variable (CV) QKD has garnered significant attention due to its high secret key generation rates and compatibility with conventional optical telecommunication infrastructure, which operates under ambient conditions. However, chip-based integration is crucial for realizing practical and scalable CV-QKD networks, and photonic integrated circuit technology is a potential solution, leveraging the on-chip integration of essential optical components onto silicon photonic circuits. Therefore, this work presents a compact, stable, and cost-effective quantum photonic CV-QKD system on a chip. Our architecture combines time- and polarization-multiplexing with high-extinction-ratio pulse generation to mitigate excess noise. At the same time, a real-time feedback control mechanism compensates for polarization drift, ensuring robust system performance. Fiber-based evaluations reveal secret key generation rates of 2.55 Mbps over 25 km and 0.737 Mbps over 50 km with 12 h stable operation, establishing, to our knowledge, a new benchmark for integrated photonic CV-QKD systems with both the transmitter and receiver on-chip. These results mark a significant milestone in on-chip quantum communication, paving the way for widespread adoption of photonic integrated circuits in future metropolitan quantum-secure networks.
We report here a new side channel attack on a practical continuous-variable (CV) quantum key distribution (QKD) system. Inspired by blinding attack in discrete-variable QKD, we formalize an attack strategy by inserting an external light into a CV QKD system implemented Gaussian-modulated coherent state protocol and show that our attack can compromise its practical security. In this attack, we concern imperfections of a balanced homodyne detector used in CV QKD. According to our analysis, if one inserts an external light into Bob’s signal port, due to the imperfect subtraction from the homodyne detector, the leakage of the external light contributes a displacement on the homodyne signal which causes detector electronics saturation. In consequence, Bob’s quadrature measurement is not linear with the quadrature sent by Alice. By considering such vulnerability, a potential Eve can launch a full intercept-resend attack meanwhile she inserts an external light into Bob’s signal port. By selecting proper properties of the external light, Eve actively controls the induced displacement value from the inserted light which results saturation of homodyne detection. In consequence, Eve can bias the excess noise due to the intercept-resend attack and the external light, such that Alice and Bob believe their excess noise estimation is below the null key threshold and they can still share a secret key. Our attack shows that the detector loopholes also exist in CV QKD, and it seems influence all the CV QKD systems using homodyne detection, since all the practical detectors have finite detection range.
Continuous-variable quantum key distribution (CVQKD) has attracted extensive attention due to its compatibility and low costs. However, bandwidth mismatch exists to varying degrees between the transmitter and receiver. This may prevent frequency components carrying modulation information from being fully perceived by the legitimate party. In this paper, we identify a practical security loophole caused by bandwidth mismatch and propose a corresponding spectral attack scheme. Different from previous approaches that exploit security loopholes to conceal the excess noise introduced by intercept-resend attacks, this scheme can directly obtain raw-key information without introducing additional disturbances. A proof-of-principle attack on a CVQKD system with filtering operation is constructed to verify the feasibility. Experimental results indicate that Eve can obtain enough information to render the system insecure if this practical security loophole is ignored. Based on the identified security loophole, corresponding defense strategies are proposed. This work helps bridge the gap between theoretical models and practical implementations, providing a reference for defense design in practical quantum communication systems.
Integrated quantum key distribution (QKD) systems based on photonic chips have high scalability and stability, and are promising for further construction of global quantum communications networks. On-chip quantum light sources are a critical component of a fully integrated QKD system; especially a continuous-variable QKD (CV-QKD) system based on coherent detection, which has extremely high requirements for the light sources. Here, for what we believe is the first time, we designed and fabricated two on-chip tunable lasers for CV-QKD, and demonstrated a high-performance system based on these sources. Because of the high output power, fine tunability, and narrow linewidth, the involved on-chip lasers guarantee the accurate shot-noise-limited detection of quantum signals, center wavelength alignment of nonhomologous lasers, and suppression of untrusted excess noise. The system’s secret key rate can reach 0.75 Mb/s at a 50 km fiber distance, and the secure transmission distance can exceed 100 km. Our results mark a breakthrough toward building a fully integrated CV-QKD, and pave the way for a reliable and efficient terrestrial quantum-secure metropolitan area network.
In the evolving field of Continuous Variable Quantum Key Distribution (CV-QKD), notable for its synergistic potential with existing optical communication infrastructures, a high channel capacity, and an anticipated surge in secret rates, the Measurement Device Independent (MDI) framework stands as a bulwark against side-channel vulnerabilities at the measurement juncture [1] –[4]. Recent years have witnessed quantum photonics technology leapfrogging into a realm that promises the realization of fully integrated CV-MDI-QKD transmitter terminals, a cornerstone for large-scale CV-MDI-QKD networks. However, integrating high-efficiency on-chip light sources while effectively navigating the treacherous waters of practical security challenges remains a formidable task [5], [6]. This study is pioneering in its focus on the practical security intricacies stemming from imperfections in on-chip light sources within CV-MDI-QKD systems. We propose defense mechanisms tailored to shield against the risks associated with source defects, thereby laying a robust foundation for secure, reliable on-chip CV-MDI-QKD transmission terminals. This advancement is a critical enabler for the widespread adoption of CV-MDI-QKD, signaling a paradigm shift in secure communications.