Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Elimination of Spatial Side-Channel Information for Compact Quantum Key Distribution Sendersb

Wei-Shao Huang, Wei Zhang, Yidong Huang

Published Sep 1, 2019• 1 citation
Publisher

Abstract

For a compact quantum key distribution (QKD) sender for the polarization encoding BB84 protocol, an eavesdropper could take a side-channel attack by measuring the spatial information of photons to infer their polarizations. The possibility of this attack can be reduced by introducing an aperture in the QKD sender, however, the effect of the aperture on the QKD security lacks of quantitative analysis. In this paper, we analyze the mutual information between the actual keys encoded at this QKD sender and the inferred keys at the eavesdropper (Eve), demonstrating the effect of the aperture to eliminate the spatial side-channel information quantitatively. It shows that Eve’s potential on eavesdropping spatial side-channel information is totally dependent on the optical design of the QKD sender, including the source arrangement and the aperture. The height of compact QKD senders with integrated light-emitting diode (LED) arrays could be controlled under several millimeters, showing great potential on applications in portable equipment.

DOI
10.11989/jest.1674-862x.90416014

Related papers

Experimental Side Channel Analysis of BB84 QKD Source

Ayan Biswas, Anindya Banerji, Pooja Chandravanshi +2 more

A typical implementation of BB84 protocol for quantum communication uses four laser diodes for transmitting weak coherent pulses, which may not have the same characteristics. We have characterized these lasers for mismatch in various parameters such as spectral width, pulse width, spatial mode, peak wavelength, polarization and their arrival times at the receiver. This information is utilized to calculate possible information leakage through side channel attacks by evaluating mutual information between source and eavesdropper. Based on our experimental observations of cross correlation between parameter values for different laser diodes, we suggest methods to reduce information leakage to Eve.

arXiv:2106.10500•IEEE Journal of Quantum Electronics•Sep 9, 2021•26 citations

Spatial Mode Side Channels in Free-Space QKD Implementations

Markus Rau, Tobias Vogl, Giacomo Corrielli +4 more

The quantum key distribution protocol uses one degree of freedom of a single quantum system to encode information. If this information has correlations with the system's other degrees of freedom, or if the measurement efficiencies on the receiver side depend on them, a security loophole called side channel is created. An eavesdropper can exploit it to gain information without disturbing the system, and thus, without revealing the attack. Here, we analyze side channels in a free-space QKD sender and receiver implementation and focus especially on the dependencies and side channels for the spatial degree of freedom.

IEEE Journal of Selected Topics in Quantum Electronics•Nov 20, 2014•34 citations

Bounding light source side channels in QKD via Hong-Ou-Mandel interference

Alexander Duplinskiy, Сыч Денис Васильевич

Side-channel attacks on practical quantum key distribution systems compromise its security. Although some of these attacks can be taken into account, the general recipe of how to eliminate all side-channel flaws is still missing. In this work, we propose a method for estimation of the total passive side-channel information leakage from the Alice's light source. The method relies on Hong-Ou-Mandel interference between different signals emitted by Alice, which reveals their overall mode mismatch without the necessity to measure all individual degrees of freedom independently. We include experimental values of interference visibility in the security proof for the decoy-state BB84 protocol, and lower-bound the secure key rate for realistic light sources. The obtained results provide a tool that can be used for certification of the current QKD systems and pave the way towards the loophole-free design of the future ones.

arXiv:1908.04703•Aug 13, 2019•0 citations

Practical Side-Channel Attack on Free-Space QKD Systems With Misaligned Sources and Countermeasures

Pablo Arteaga-Díaz, Daniel Cano, Verónica Fernández

Practical implementations of quantum key distribution (QKD) protocols can introduce additional degrees of freedom in the quantum states that may render them distinguishable to an eavesdropper. This is the case of QKD systems using a different laser source to generate each quantum states, which can lead to temporal, spectral and/or spatial differences among them that can be exploited by a malicious party to extract information of the key. In this work we characterize, and experimentally verify, a side-channel attack on spatially distinguishable states against free-space QKD systems with misaligned laser sources. Specifically, for those emitting Gaussian beams, which is the most common case in free-space QKD. The attack makes theoretically unsafe any QKD system with any angular misalignment between the laser sources. Finally, we propose two countermeasures to eliminate the spatial distinguishability and secure the key exchange.

IEEE Access•Jan 1, 2022•22 citations

Practical Long-Distance Side-Channel-Free Quantum Key Distribution

Xiang‐Bin Wang, Xiao-Long Hu, Zong‐Wen Yu

Quantum key distribution (QKD) can provide secure communication even when an eavesdropper (the villainous ``Eve'') completely controls the channel. In practice, though, side-channel effects exist due to device imperfections, and Eve can still intercept information via a side channel. Thus the authors devise a QKD scheme that is both free of side channels in the source state and measurement-device-independent. While some other protocols can also achieve side-channel-free security, this one is based on mature technology without any demand for local detection efficiency, and works for distances greater than 200 km, even though the misalignment error rate may be as large as 20%.

arXiv:1811.01263•Physical Review Applied•Nov 14, 2019•34 citations

The practical issues of side-channel-secure quantum key distribution

Cong Jiang, Hu, Xiao-Long, Zong‐Wen Yu +2 more

Quantum Key Distribution (QKD) leverages the principles of quantum mechanics to provide theoretically unconditional security for cryptographic key sharing. However, practical implementations remain vulnerable due to non-ideal devices and potential security loopholes at both the source and detection sides of QKD systems. The side-channel-secure (SCS) protocol addresses these challenges by encoding bits in vacuum and non-vacuum states and introducing a third-party measurement node, thereby repelling attacks targeting the detection side as well as external lab attacks on the source side. In this work, we consider the state-dependent correlated errors and Trojan-horse attack while preserving the SCS protocol's key advantage-specifically, requiring only upper bounds on intensities characterization without needing a full description of quantum states in infinite dimensions. Numerical results demonstrate that when the reflected light intensity from Trojan-horse attacks falls below $10^{-6}$, Eve can scarcely extract additional key information from the reflections. This work makes the SCS protocol more practical.

arXiv:2508.15197•Aug 21, 2025•0 citations
For a compact quantum key distribution (QKD) sender for the polarization encoding BB84 protocol, an eavesdropper could take a side-channel attack by measuring the spatial information of photons to infer their polarizations. The possibility of this attack can be reduced by introducing an aperture in the QKD sender, however, the effect of the aperture on the QKD security lacks of quantitative analysis. In this paper, we analyze the mutual information between the actual keys encoded at this QKD sender and the inferred keys at the eavesdropper (Eve), demonstrating the effect of the aperture to eliminate the spatial side-channel information quantitatively. It shows that Eve’s potential on eavesdropping spatial side-channel information is totally dependent on the optical design of the QKD sender, including the source arrangement and the aperture. The height of compact QKD senders with integrated light-emitting diode (LED) arrays could be controlled under several millimeters, showing great potential on applications in portable equipment.
A typical implementation of BB84 protocol for quantum communication uses four laser diodes for transmitting weak coherent pulses, which may not have the same characteristics. We have characterized these lasers for mismatch in various parameters such as spectral width, pulse width, spatial mode, peak wavelength, polarization and their arrival times at the receiver. This information is utilized to calculate possible information leakage through side channel attacks by evaluating mutual information between source and eavesdropper. Based on our experimental observations of cross correlation between parameter values for different laser diodes, we suggest methods to reduce information leakage to Eve.
The quantum key distribution protocol uses one degree of freedom of a single quantum system to encode information. If this information has correlations with the system's other degrees of freedom, or if the measurement efficiencies on the receiver side depend on them, a security loophole called side channel is created. An eavesdropper can exploit it to gain information without disturbing the system, and thus, without revealing the attack. Here, we analyze side channels in a free-space QKD sender and receiver implementation and focus especially on the dependencies and side channels for the spatial degree of freedom.
Side-channel attacks on practical quantum key distribution systems compromise its security. Although some of these attacks can be taken into account, the general recipe of how to eliminate all side-channel flaws is still missing. In this work, we propose a method for estimation of the total passive side-channel information leakage from the Alice's light source. The method relies on Hong-Ou-Mandel interference between different signals emitted by Alice, which reveals their overall mode mismatch without the necessity to measure all individual degrees of freedom independently. We include experimental values of interference visibility in the security proof for the decoy-state BB84 protocol, and lower-bound the secure key rate for realistic light sources. The obtained results provide a tool that can be used for certification of the current QKD systems and pave the way towards the loophole-free design of the future ones.
Practical implementations of quantum key distribution (QKD) protocols can introduce additional degrees of freedom in the quantum states that may render them distinguishable to an eavesdropper. This is the case of QKD systems using a different laser source to generate each quantum states, which can lead to temporal, spectral and/or spatial differences among them that can be exploited by a malicious party to extract information of the key. In this work we characterize, and experimentally verify, a side-channel attack on spatially distinguishable states against free-space QKD systems with misaligned laser sources. Specifically, for those emitting Gaussian beams, which is the most common case in free-space QKD. The attack makes theoretically unsafe any QKD system with any angular misalignment between the laser sources. Finally, we propose two countermeasures to eliminate the spatial distinguishability and secure the key exchange.
Quantum key distribution (QKD) can provide secure communication even when an eavesdropper (the villainous ``Eve'') completely controls the channel. In practice, though, side-channel effects exist due to device imperfections, and Eve can still intercept information via a side channel. Thus the authors devise a QKD scheme that is both free of side channels in the source state and measurement-device-independent. While some other protocols can also achieve side-channel-free security, this one is based on mature technology without any demand for local detection efficiency, and works for distances greater than 200 km, even though the misalignment error rate may be as large as 20%.
Quantum Key Distribution (QKD) leverages the principles of quantum mechanics to provide theoretically unconditional security for cryptographic key sharing. However, practical implementations remain vulnerable due to non-ideal devices and potential security loopholes at both the source and detection sides of QKD systems. The side-channel-secure (SCS) protocol addresses these challenges by encoding bits in vacuum and non-vacuum states and introducing a third-party measurement node, thereby repelling attacks targeting the detection side as well as external lab attacks on the source side. In this work, we consider the state-dependent correlated errors and Trojan-horse attack while preserving the SCS protocol's key advantage-specifically, requiring only upper bounds on intensities characterization without needing a full description of quantum states in infinite dimensions. Numerical results demonstrate that when the reflected light intensity from Trojan-horse attacks falls below 10−610^{-6}10−6, Eve can scarcely extract additional key information from the reflections. This work makes the SCS protocol more practical.