Measurements towards providing security assurance for a chip-scale QKD system
Andy Hart, Robert A. Kirkwood, Henry Semenenko, Philip Sibson, Christopher J. Chunnilall, Anthony Vaquero-Stainer, Alastair G. Sinclair, Viacheslav Burenkov, Chris Erven, Mark G. Thompson
Quantum key distribution (QKD) is one of the most commercially-advanced quantum optical technologies operating in the single-photon regime. The commercial success of this disruptive technology relies on customer trust. Network device manufacturers have to meet stringent standards in order to ensure the operational security of their devices. The National Physical Laboratory (NPL) and the University of Bristol (Bristol) are working to produce a suite of tests to determine the operating characteristics and implementation security of chip-scale quantum devices designed for security purposes. These tests will inform and provide assurance to potential customers of such devices. Results from initial measurements performed on the Bristol chip-scale transmitter and receiver are presented, with the aim of informing the development of the system.
Quantum key distribution (QKD) is one of the most commercially-advanced quantum optical technologies operating in the single-photon regime. The commercial success of this disruptive technology relies on customer trust. Network device manufacturers have to meet stringent standards in order to ensure the operational security of their devices. The National Physical Laboratory (NPL) and the University of Bristol (Bristol) are working to produce a suite of tests to determine the operating characteristics and implementation security of chip-scale quantum devices designed for security purposes. These tests will inform and provide assurance to potential customers of such devices. Results from initial measurements performed on the Bristol chip-scale transmitter and receiver are presented, with the aim of informing the development of the system.
Improvement in secure transmission of information is an urgent need for governments, corporations and individuals. Quantum key distribution (QKD) promises security based on the laws of physics and has rapidly grown from proof-of-concept to robust demonstrations and deployment of commercial systems. Despite these advances, QKD has not been widely adopted, and large-scale deployment will likely require chip-based devices for improved performance, miniaturization and enhanced functionality. Here we report low error rate, GHz clocked QKD operation of an indium phosphide transmitter chip and a silicon oxynitride receiver chip-monolithically integrated devices using components and manufacturing processes from the telecommunications industry. We use the reconfigurability of these devices to demonstrate three prominent QKD protocols-BB84, Coherent One Way and Differential Phase Shift-with performance comparable to state-of-the-art. These devices, when combined with integrated single photon detectors, pave the way for successfully integrating QKD into future telecommunications networks.
Quantum key distribution (QKD) is a technology that allows two users to communicate with theoretically perfect security using standard optical fibres. This is possible by transmitting the key on single photons, meaning a measurement by an eavesdropper disturbs the system in a way observable to the legitimate parties. The technology has advanced since the first protocol proposed in 1984, to the stage where there are now many protocols that can be experimentally implemented. These protocols have allowed secure keys to be generated over distances greater than 400 km and with secure key rates over 10 Mbit/s. In a metropolitan QKD network, it would be desirable for as many users to be connected as possible. Unfortunately, each protocol comes with different requirements on the transmitter and receiver. Even within a single protocol, different clock rates can require individualised transmitter and receiver hardware. This prohibits users from communicating with all receivers, unless they have complex transmitters with hardware for many protocols. This thesis develops a transmitter for practical QKD that is able to adapt to a number of different protocols with no changes to the hardware. The transmitter works using optical injection locking, where a pulse preparation laser adopts the phase of a phase preparation laser. Controlling the phase and intensity of the pulses in this way removes the side channel ordinarily present with direct modulation, in that the phase, intensity and frequency simultaneously change in response to an applied current. The cavity-enhanced electro-optic effect allows for the first demonstration of sub-volt half-wave phase modulation at high clock rates. The transmitter successfully demonstrates phase encoding, intensity encoding and on-demand phase randomisation. This allows for the experimental realisation and direct comparison of different QKD protocols, including one that has never before been implemented due to experimental complexity. A stable intensity modulator is also developed, based on a Sagnac interferometer. This removes a side channel in QKD systems and integrates well with the directly-modulated quantum transmitter. This development also means that the transmitter can implement all current two-party QKD protocols based on weak coherent pulses. The transmitter has the potential to become the standard transmitter for future quantum communication networks due to its stability, versatility and power efficiency. The design could also be demonstrated on a photonic chip, making it compact enough to fit in small transmitter units.
Industrial technologies based on the production, manipulation, and detection of single and entangled photons are emerging, and quantum key distribution via optical fibre is one of the most commercially-advanced. The National Physical Laboratory is developing traceable performance metrology for the quantum devices used in these technologies. This is part of a broader effort to develop metrological techniques and standards to accelerate the development and commercial uptake of new industrial quantum communication technologies based on single photons. This presentation will give an overview of the work carried out at NPL and within the wider European community, and highlight plans for the future.
As more aspects of modern society depend on digital communication, we increasingly rely on infrastructure that ensures the privacy and security of this communication. Classically, this has been provided by cryptographic protocols such as public-key encryption, in which secrets called keys are exchanged between different parties to enable secure communication. The rapid development of quantum algorithms which violate the assumptions of these protocols, however, poses a security challenge to modern cryptography. \n \nQuantum resources can also be used to strengthen cryptographic security, particularly the security of key exchange protocols. This approach, QKD, can be implemented by encoding in quantum systems such as single photons sent through free-space or a fiber. Fiber based QKD devices are already commercially available, but are fundamentally limited to distributing keys over a few hundred kilometers. To address this distance limitation, research QKD systems are being developed to exchange keys through free-space to satellites. This work considers practical challenges to building and testing both types of QKD devices. \n \nFirstly, we consider modeling and mission analysis for airborne demonstrations of QKD to stratospheric balloons and aircraft to simulate a satellite. Based on the mission parameters available for both platforms, we found aircraft platforms were more promising for testing prototype QKD satellite systems. We developed a mission planning tool to help design the flight geometries for testing the device. \n \nNext, we developed three new components for a QKD satellite prototype. The requirements for electro-optical devices in orbit are very different from lab environments, mandating new approaches to designing QKD devices. We developed a quad single photon detector package to meet the requirements for free-space links to low earth orbit. Moreover, we designed and built optical systems for analyzing the polarization of photons and an adaptive optics unit to increase the efficiency of collecting the encoded photons. All three devices were tested in conditions that simulated the time and loss of a satellite pass. \n \nFinally, we demonstrated a laser damage attack on a live commercial QKD system. Our attack injected additional optical power into the sender device to modify security-critical components. Specifically, our attack damaged the PIN diodes which monitor the encoded photon number, reducing their sensitivity or completely blinding them. Our damage could compromise the entire key, and was performed during system operation while raising no alarms. \n \nIn summary, this work shows the trade-offs of testing QKD payloads on different airborne platforms, develops components for a satellite QKD payload, and demonstrates a security vulnerability in a commercial QKD system that can fully compromise the key. These results help address practical challenges to building QKD devices, improving the security of modern cryptography.
Quantum key distribution (QKD) is a cryptographic technique that enables secure private key exchange between geographically distant parties over an insecure channel, protecting confidentiality against potential eavesdroppers. QKD has evolved significantly since its inception with the BB84 protocol proposed by Bennett and Brassard in 1984. Its theoretical foundation relies on quantum physics, particularly the uncertainty principle, the no-cloning theorem, and particle entanglement, which ensures its information-theoretic security when combined with the one-time-pad cryptographic algorithm. However, certain security loopholes persist in terms of practical implementation in commercial devices. Some vulnerabilities are associated with side-channel vectors linked to commonly used optical subcomponents, while others are more related to how existing protocols handle encoding and communication pipelines. In this work, we aim to comprehensively study the current state of security loopholes affecting QKD technology in commercial devices. We also provide a concise overview of the existing types of QKD implementations. Additionally, we offer insights into current trends and vulnerability countermeasures, paving the way for future research and novel mechanisms to enhance the implementation security of commercial QKD devices.