Power-consumption back door in quantum key distribution
Beatriz Lopes da Costa, Matías Rubén Bolaños, Ricardo Chaves, Claudio Narduzzi, Marco Avesani, Davide G. Marangon, Andrea Stanco, Giuseppe Vallone, Paolo Villoresi, Yasser Omar
Over recent decades, quantum key distribution (QKD) has arisen as a promising solution for secure communications; however, like all cryptographic protocols, implementations of QKD can open security vulnerabilities. Until now, the study of physical vulnerabilities in QKD setups has focused primarily on the optical channel. In classical cryptoanalysis, power and electromagnetic side-channel analysis are powerful techniques that can be used to access secret information about the encryption key in symmetric-key algorithms. Such attacks have rarely been used in QKD, since they require an eavesdropper to have access to Alice’s or Bob’s setup; however, security proofs of QKD protocols generally assume that these setups are secure, making it crucial to understand the security measures required to ensure this protection. In this work, we propose and implement a power side-channel analysis of a QKD system by exploiting the power consumption of the electronic driver controlling the electro-optical components of the QKD transmitter. QKD modules typically require very precise electronic drivers, such as field-programmable gate arrays (FPGAs). Here, we show that the FPGA’s power consumption can leak information about the QKD operation and consequently the transmitted key. Our results are consistent and show critical information leakage, having reached a maximum accuracy of 73.35% in predicting transmitted qubits at a 100-MHz repetition frequency. We also discuss possible countermeasures to prevent such an attack.
Over recent decades, quantum key distribution (QKD) has arisen as a promising solution for secure communications; however, like all cryptographic protocols, implementations of QKD can open security vulnerabilities. Until now, the study of physical vulnerabilities in QKD setups has focused primarily on the optical channel. In classical cryptoanalysis, power and electromagnetic side-channel analysis are powerful techniques that can be used to access secret information about the encryption key in symmetric-key algorithms. Such attacks have rarely been used in QKD, since they require an eavesdropper to have access to Alice’s or Bob’s setup; however, security proofs of QKD protocols generally assume that these setups are secure, making it crucial to understand the security measures required to ensure this protection. In this work, we propose and implement a power side-channel analysis of a QKD system by exploiting the power consumption of the electronic driver controlling the electro-optical components of the QKD transmitter. QKD modules typically require very precise electronic drivers, such as field-programmable gate arrays (FPGAs). Here, we show that the FPGA’s power consumption can leak information about the QKD operation and consequently the transmitted key. Our results are consistent and show critical information leakage, having reached a maximum accuracy of 73.35% in predicting transmitted qubits at a 100-MHz repetition frequency. We also discuss possible countermeasures to prevent such an attack.
Quantum Key Distribution (QKD) promises information-theoretic security based on the fundamental laws of quantum mechanics. However, practical implementations deviate from idealized models and are therefore susceptible to side-channel attacks that exploit physical imperfections rather than theoretical vulnerabilities. Over the past two decades, a wide range of attacks have been demonstrated against QKD systems, including those targeting detectors, sources, timing information, power consumption, and electromagnetic emissions. This paper addresses a selection of a few side-channel attacks reported in the literature, classifying them according to their underlying physical mechanisms and attack strategies. We analyze their impact on the security of different QKD protocols and platforms, and highlight how experimental demonstrations have shaped the community's understanding of implementation security. In addition, we present and evaluate mitigation techniques proposed to date, such as device-independent and measurement-device-independent QKD, hardware countermeasures, monitoring strategies, and so on. We also identify open challenges and promising directions for enhancing the robustness of future quantum communication systems.
The security of current key exchange protocols such as Diffie-Hellman key exchange is based on the hardness of number theoretic problems. However, these key exchange protocols are threatened by weak random number generators, advances to CPU power, a new attack from the eavesdropper, and the emergence of a quantum computer. Quantum Key Distribution (QKD) addresses these challenges by using quantum properties to exchange a secret key without the risk of being intercepted. Recent developments on the QKD system resulted in a stable key generation with fewer errors so that the QKD system is rapidly becoming a solid commercial proposition. However, although the security of the QKD system is guaranteed by quantum physics, its careless implementation could make the system vulnerable. In this paper, we proposed the first side-channel attack on plug-and-play QKD system. Through a single electromagnetic trace obtained from the phase modulator on Alice's side, we were able to classify the electromagnetic trace into four classes, which corresponds to the number of bit and basis combination in the BB84 protocol. We concluded that the plug-and-play QKD system is vulnerable to side-channel attack so that the countermeasure must be considered.
The Quantum Key Distribution (QKD) method leverages the principles of quantum mechanics to securely create and distribute private keys using quantum systems and an authenticated public classical channel. Despite offering informationtheoretical security, its physical implementations often suffer from unintended information leakage, known as side channels, which eavesdroppers can exploit to obtain the private key. This study introduces a classical-side-channel attack on the privacyamplification step of a general QKD protocol based on matrix hashing, utilizing machine-learning techniques to analyze powerconsumption leakage. Through multiple simulated scenarios, the study found that the gradient-boosting machine consistently outperformed other models, recovering the entire private key for high measuring-instrument sampling rates, regardless of the hashing matrix size and noise level tested. Additionally, the study proposes a strategy based on analyzing the confusion matrices of the model to facilitate a brute-force search for the critical feasible in the case of a non-perfect model. Furthermore, the study discusses countermeasures such as noise insertion, masking, and randomization techniques, potentially restoring the QKD protocol's information-theoretical security. This work demonstrates that machine-learning techniques can effectively characterize the leakages in a QKD implementation and create potent attacks.
Cryptography plays a crucial and significant part in key transmission between two users. To send the keys in a secure manner, quantum implementations are used. A recent method of distributing keys across users is known as quantum key distribution. There is a substantial disconnect between quantum key distribution (QKD) theory and practice in this regard. Gadgets no longer meet the security evidence's assumptions. This hole is accessed as an input here. A simple and direct measurement methodology that is independent of the QKD device and is primarily based on any potential flaws and/or failures. A quantum language exchange facet channel that is part of the QKD device. Our simplest technique is experimentally give up to one unpaired parameter for each transmitted pulse. This explains the high dissatisfaction with the source. Also, unlike DI (Device Independent) QKD, Stats leaked from user labs critical to ensuring QKD's security avatar. In that sense, its security is more than what DI QKD offers, but it provides a secret.
The importance of secure and high-rate information transmission cannot be understated in today's society. Unfortunately, a security crisis is impending due to the development of quantum computing technologies which can break current encryption schemes. A promising solution is quantum key distribution (QKD), which offers information-theoretic security. However, practical implementations of QKD do not conform to the idealized security assumptions that are made in QKD security proofs and therefore form security loopholes. The discovery of the measurement-device-independent QKD (MDI QKD) protocol presented a rapid leap in QKD research, as it effectively closes all side channels at the detection end of QKD setups, while maintaining experimental feasibility. Naturally, a major remaining obstacle in QKD research is the vulnerability of practical sources. As the clock rate of QKD systems advances into the GHz range, specific imperfections at the source arise. The goal of this PhD thesis is to conduct characterizations of source imperfections (especially those arising from GHz modulation), quantify their impact on security, and find methods to mitigate them. Specifically, this thesis presents the following studies. A) Identification and analysis of a novel side channel in sources using a Faraday mirror for temperature-stabilized polarization modulation, leading to time-dependent passive leakage of quantum states. We demonstrate that precise side-channel characterization (rather than the pessimistic approximations commonly used in the literature) can improve the estimated secret key rate by multiple orders of magnitude. B) Identification and analysis of a new class of source side channels (hidden multidimensional modulation side channels), using high-speed time-varying encoding as an illustrative case example (which we characterize using experimental and simulation-based methods). We demonstrate that hidden degrees of freedom, such as time, may be coupled to the encoding process, enabling unambiguous state discrimination attacks. In our illustrative case example, this causes the maximum secure transmission distance to be reduced by over 50%. C) Experimental and simulation-based characterization of phase correlations at GHz repetition rates when using electro-optic phase modulation for phase/polarization encoding. Our findings indicate that pattern-dependent phase deviations are on the order of 0.01pi. D) Design and experimental demonstration of a path-selection modulation source -- a source using no active phase modulation components (to mitigate the side channels arising from such components). Phase randomization is achieved through gain-switching and polarization encoding is achieved by randomly selecting between multiple paths, each path corresponding to one of the desired encoded states. Overall, by identifying and characterizing multiple source side channels, this thesis underscores the importance of avoiding unwarranted assumptions regarding the security of QKD sources. Hidden imperfections can introduce significant security vulnerabilities, and these must be continually identified and analyzed. Furthermore, this thesis highlights the value of advancing key rate analysis techniques that can accommodate a broad range of implementation flaws while producing tight security bounds, thereby enabling precise characterization of the information leakage arising from such imperfections. Finally, this thesis emphasizes that active modulators, in general, constitute a major source of potential side channels, highlighting the importance of exploring modulator-free sources. The path-selection modulation scheme presented here provides a practically feasible example of such a source.
Nowadays, quantum key distribution (QKD) has gradually moved from the laboratory to practical applications. However, the inherent imperfections of practical QKD devices would cause side channels. Among them, there is one critical side channel vulnerability that is often overlooked, i.e., information leakage of the electromagnetic field (LEMF). In this work, we carry out systematic investigations on the LEMF by utilizing a practical phase-coding BB84 QKD system as an example. We demonstrate that LEMF from the widely used modulators could be exploited by a malicious eavesdropper to obtain corresponding encoding information assisted with artificial intelligence algorithms, posing a serious threat for practical QKD systems. To solve this problem, we conduct security analysis on LEMF and build a mathematical model on the final secure key rate. Moreover, we give out corresponding countermeasures to reduce information leakage and thus enhance practical security of QKD systems. Therefore, our current work can provide important theoretical and experimental foundations for the future development of secure large-scale quantum communication networks.