In this thesis an unprecedented cyber-physical attack which can be a game changer in the quantum cryptosystems' security is explained. This attack is the first non-optical patented intercept in quantum field that is based on a security issue in the physical layer of the quantum communication and key distribution systems. We experimentally and theoretically showed that the bit contents of a quantum key transmission system can be intercepted from far away by exploiting the ultrawideband electromagnetic signals radiated from the hi-voltage avalanche effect of the single photon detectors. This concept was a significant hidden secret based on the physical nature of the single photon detectors that are generally used in quantum key distribution. It has been proved theoretically and experimentally that any Geiger-mode avalanche photodiode that is used inside single photon detectors, systematically acts like a downconverter that converts the optical-wavelength photons to radio-wavelength photons. Our experiments also showed that the radiated waveforms captured by an ultrawideband antenna can be used as a unique fingerprint to find which photodiode in the cryptosystem has absorbed a photon. These fingerprints were fed to a deep learning neural network as training data, and after training, the neural network was able to clone the bit content of quantum transmission with high accuracy.
In this thesis an unprecedented cyber-physical attack which can be a game changer in the quantum cryptosystems' security is explained. This attack is the first non-optical patented intercept in quantum field that is based on a security issue in the physical layer of the quantum communication and key distribution systems. We experimentally and theoretically showed that the bit contents of a quantum key transmission system can be intercepted from far away by exploiting the ultrawideband electromagnetic signals radiated from the hi-voltage avalanche effect of the single photon detectors. This concept was a significant hidden secret based on the physical nature of the single photon detectors that are generally used in quantum key distribution. It has been proved theoretically and experimentally that any Geiger-mode avalanche photodiode that is used inside single photon detectors, systematically acts like a downconverter that converts the optical-wavelength photons to radio-wavelength photons. Our experiments also showed that the radiated waveforms captured by an ultrawideband antenna can be used as a unique fingerprint to find which photodiode in the cryptosystem has absorbed a photon. These fingerprints were fed to a deep learning neural network as training data, and after training, the neural network was able to clone the bit content of quantum transmission with high accuracy.
A newfound security breach in the physical nature of single photon detectors that are generally used in quantum key distribution is explained, we found that the bit contents of a quantum key transmission system can be intercepted from far away by exploiting the ultrawideband electromagnetic signals radiated from hi-voltage avalanche effect of single photon detectors. It means that in fact any Geiger mode avalanche photodiode that is used inside single photon detectors systematically acts like a downconverter that converts the optical-wavelength photons to radio-wavelength photons that can be intercepted by an antenna as side channel attack. Our experiment showed that the radiated waveforms captured by the antenna can be used as a fingerprint. These finger prints were fed to a deep learning neural network as training data, and after training the neural network was able to clone the bit content of quantum transmission.
The well-known RF penetration method is implemented on the quantum cryptosystems. In this study, RF radiations from the single photon detectors in a quantum key distribution system are intercepted. It was found that the data contents of a quantum transmission system can be detected from the vicinity of the receiving parties by exploiting the radiations of avalanche effect of single photon detectors. We showed that any Geiger-mode avalanche photodetector acts like a downconverter that converts the optical-wavelength photons to radio-wavelength photons. In our experiment, the fingerprints of the avalanche radiations from commercial single photon detectors were fed to a trained deep learning neural network, and the bit content of quantum transmission was cloned with >99% accuracy up to a distance of 2 meters from the detectors. We also speculate on the enhancement of the key cloning accuracy and range of the eavesdropping.
Quantum key distribution (QKD) allows two users to communicate with information theoretic security by encoding information on single photons. This security is based on the laws of physics and as such can never be broken in theory. However, in practice, components do not always behave according to their theoretical models and these deviations can be exploited by an eavesdropper. In recent years, exposing loopholes in QKD systems, known as quantum hacking, has attracted significant attention. The components most susceptible to being hacked are the single-photon detectors, often avalanche photodiodes (APDs), as they are directly exposed to the optical channel. Whilst measurement-device-independent QKD removes detector vulnerability from the system, secure key rates with this technique can be much lower than point-to-point links. As such, mitigating attacks on QKD systems is a pressing challenge in QKD. In this thesis, the focus is on a special class of detectors, self-differencing APDs (SD-APDs), which have facilitated state-of-the art demonstrations of QKD. The susceptibility of SD-APDs to blinding attacks, the most explored and successful attack to date, was investigated and it was shown that by following best practice for their operation, such an attack would be unsuccessful. We have also proposed and developed a countermeasure such that the onus for appropriate operation could be removed from the user. We have also explored an arguably more dangerous attack, in the form of the after-gate attack. We have shown that delayed detection events, ordinarily considered detrimental in QKD, can provide inherent protection against this attack. Finally, backflashes in GHz-gated APDs were investigated for the first time and it was shown that threat they pose to QKD security is negligible. These results highlight the inherent protection to a number of attacks that self-differencing APDs possess. We stress that the findings presented in this thesis are also applicable to other types of fast-gated InGaAs APDs that don't possess self-differencing circuitry.
Quantum Information Technology is a new multi-disciplinary area which has received a lot of attention due to its promises and its high potential in solving problems still unsolved. In this big area, Quantum Communication is too much developed. In this subarea, Quantum Key Distribution is the most advanced field. It permits two parties, named Alice and Bob, sharing a cryptography key through a secure channel (guaranteed by laws of quantum mechanics). The most of Quantum Key Distribution Systems run over optical fiber links and, in these systems, the most important part is the Single-Photon Detector. Single-Photon Detector is an equipment able to absorb a photon and generate a TTL pulse. Thus, in an ideal Single-Photon Detector, each photon incoming must trigger a TTL pulse at the output. Since the energy level of a single-photon is too much low, an avalanche photodiode is used to perform the photon absorption-carrier generation process, once this photodiode if correctly biased can trigger a detectable avalanche of carriers. After the avalanche has been started, it must be quenched in order to avoid any damage to the photodiode, which is made by an avalanche quenching circuit. The avalanche photodiode is the most important element of a Single-Photon Detector and its characterization requires much attention. In this context, this dissertation deals with theoretical and practical aspects of Single-Photon Detectors for Quantum Communication. It starts from the theory of avalanche photodiodes and quenching circuits (numerical results of quenching circuits are also shown) and follows until the characterization of a home-made Single-Photon Detector and its applications in Metrology of optical devices and in Photon-Number Resolution as well.
Quantum communications and quantum cryptography are developing rapidly during the last decades caused partly by a fast progress in quantum computing. Quantum cryptography provides an unconditionally secure way of communicating whereas traditional classical cryptographic protocols are likely to be broken by super powerful quantum computers. In the past few years distances covered by quantum communications have increased by an order of magnitude. To provide a global coverage for the quantum networks, a satellite based quantum communications is the most promising solution. \n \nAs an emerging field, QKD systems are still under evolution process. Despite outstanding security proven theoretically, it has loopholes caused by their implementations. To test QKD, find the possible loopholes and suggest ways to fix them, is a job of many scientific groups. \nIn this thesis I start with presenting my work for a securing test of a commercial QKD system Clavis2. A Trojan-horse attack on Bob's apparatus was prepared by testing reflections and transmissions of all optical components in Bob's scheme. The attack was implemented and found to be unsuccessful at the tested wavelengths due to afterpulsing effect in Bob's single-photon detectors reacting to the bright light attack pulses. \n \nThree chapters of the thesis are dedicated to custom built single-photon detectors (SPDs) based on commercial Silicon avalanche photodiodes (APDs). Those detectors demonstrate parameters that altogether are not possible to find in commercially available SPDs, especially if combined with a very compact size. One of the in-lab-built SPDs was implemented in 143 km teleportation experiment, where a low dark count rate was crucial for the success of the experiment. The next generation SPD is already built, characterized and ready to be implemented. \n \nAnother 4-channel SPD was built as a prototype for a quantum satellite SPD. It has light weight, low electrical power consumption, low dark count rate and decent other parameters. It was used in the airborne demonstration of QKD receiver payload experiment, when a secret key was successfully generated between a moving aircraft and a ground station. \n \nSPDs installed on a satellite have to be able to work in the harsh space environment during a mission life time. Space radiation dramatically increases dark count rate of APDs. The last project presented in the thesis committed to a radiation test of three types of APDs and one type of photo multiplier tube. The experiment included characterization of all SPDs before and after irradiation by four levels of proton radiation, equivalent to 3 months - 2 years duration in a 600 km low Earth orbit. Three methods for mitigating radiation damage were tested and found to be successful with perspective to use some of them on a quantum satellite to extent life time of SPDs. \n \nTo summarize, this work makes a contribution to the development of SPDs for global quantum communications.
While quantum key distribution (QKD) protocols are proven secure based on fundamental physical laws, side channels may allow an eavesdropper to obtain information unnoticeably. We present a profiled [1] side-channel attack using a deep convolutional neural network to analyze the classical, radio-frequency electromagnetic emissions from the electronics of a QKD sender. At a few centimeters from the device, we are able to recover virtually all information about the secret key. Furthermore, we can still observe traces of electromagnetic radiation from the device at distances of a few meters using a wideband antenna. Our methods are designed to be easily adaptable and may serve as a starting point for assessing the presence of this side channel for other devices.