Quantum cryptography has been proven to be the only practical method for fast distribution of secret keys needed for encryption. It enables absolutely secure information transfer from one party to another and allows for the detection of an eavesdropper without sacrificing security. This project involved designing and building a quantum cryptography device. This device has applications in many fields, including internet security as well as military communications. The data are encoded on single photons, which are sent through free space over a distance of about 30 cm. The electronics, which control the device however, are equally suitable for operation with fibre optic cables. The device was designed to operate in dark conditions within a laboratory. Currently, no research group has demonstrated transmission speeds faster than 8 kb/s. The aim of this project was to achieve bit rates faster than 10 kb/s, while operating under strict economic constraints. Although quantum cryptography was not demonstrated in the laboratory due to problems with the detector, the emission end, which generates single photons of light with one of two different polarisations, was shown to work as it was designed. The current design has limited commercial future due to the dark conditions under which the communication must take place. The project however has demonstrated that quantum cryptography is getting closer to becoming a reality.
Quantum cryptography has been proven to be the only practical method for fast distribution of secret keys needed for encryption. It enables absolutely secure information transfer from one party to another and allows for the detection of an eavesdropper without sacrificing security. This project involved designing and building a quantum cryptography device. This device has applications in many fields, including internet security as well as military communications. The data are encoded on single photons, which are sent through free space over a distance of about 30 cm. The electronics, which control the device however, are equally suitable for operation with fibre optic cables. The device was designed to operate in dark conditions within a laboratory. Currently, no research group has demonstrated transmission speeds faster than 8 kb/s. The aim of this project was to achieve bit rates faster than 10 kb/s, while operating under strict economic constraints. Although quantum cryptography was not demonstrated in the laboratory due to problems with the detector, the emission end, which generates single photons of light with one of two different polarisations, was shown to work as it was designed. The current design has limited commercial future due to the dark conditions under which the communication must take place. The project however has demonstrated that quantum cryptography is getting closer to becoming a reality.
The secure distribution of the secret random bit sequences known as {open_quotes}key{close_quotes} material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is an emerging technology for secure key distribution with single-photon transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non-orthogonal single-photon states to generate shared key material over multi-kilometer optical fiber paths and over line-of-sight links. In both cases, key material is built up using the transmission of a single-photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. In our optical fiber experiment we have performed quantum key distribution over 24-km of underground optical fiber using single-photon interference states, demonstrating that secure, real-time key generation over {open_quotes}open{close_quotes} multi-km node-to-node optical fiber communications links is possible. We have also constructed a quantum key distribution system for free-space, line-of-sight transmission using single-photon polarization states, which is currently undergoing laboratory testing. 7 figs.
The secure distribution of the secret random bit sequences known as 'key' material, is an essential precursor to their use for the encryption and decryption of confidential communications. Quantum cryptography is a new technique for secure key distribution with single-photon transmissions: Heisenberg's uncertainty principle ensures that an adversary can neither successfully tap the key transmissions, nor evade detection (eavesdropping raises the key error rate above a threshold value). We have developed experimental quantum cryptography systems based on the transmission of non- orthogonal photon polarization states to generate shared key material over line-of-sight optical links. Key material is built up using the transmission of a single-photon per bit of an initial secret random sequence. A quantum-mechanically random subset of this sequence is identified, becoming the key material after a data reconciliation stage with the sender. We have developed and tested a free-space quantum key distribution (QKD) system over an outdoor optical path of approximately 1 km at Los Alamos National Laboratory under nighttime conditions. Results show that free-space QKD can provide secure real-time key distribution between parties who have a need to communicate secretly. Finally, we examine the feasibility of surface to satellite QKD.
An important issue in today’s information society is the security of data transmission against potential intruders, which always put at risk the confidentiality. Current methods to increase security require that the two parties wishing to transmit information, exchange or share one or more security keys. Once the key has been identified, the information can be transferred in a provable secure way using a one-time pad, i. e. the key length is as long as the plaintext. Therefore, the security of the information transmission is based exclusively on the security of the key exchange. Quantum cryptography, or more precisely quantum key distribution (QKD), guarantees absolutely secure key distribution based on the principles of quantum physics, according to which it is not possible to measure or reproduce a state (e.g. polarization or phase of a photon) without being detected. The key is generated out from the measurement of the information encoded into specific quantum states of a photon, named qubits. For example, a qubit can be created using properties such as the polarization or the phase of a photon. Achieved goals of this thesis are the development of a new class of high speed integrated photonic sources for applications in quantum key distribution systems, capable of producing unprecedented qubit rates (100 Mbps - 1 Gbps) and transmitting those over larger distances than those achieved so far (> 200 km). More specifically the work has been focused on developing faint pulse sources which can be used in very demanding environmental conditions, such as those in Space. For the development of these sources, apart from the optical design, essential is the opto-mechanical engineering as well as the integration with the electronics. One of the objectives was to achieve very high level of integration and power efficiency, e.g. volumes and power consumption between 10 and 100 times smaller than those typical of a laboratory experiment. Moreover, work in related parts of a whole QKD transmission system has been carried out. In particular, a new scheme for a compact, fast and simple random number generator has been demonstrated successfully achieving a random number generation rate of 1:1 Gbps. Also, during the course of this thesis, the development and engineering of a free-space QKD optical link has been initiated. This thesis makes use of novel ideas to alternatively demonstrate proof-of- concept experiments, which could then further develop into commercial products. To this end, close collaborations with world-wide leading companies in the field have been established. The Optoelectronics Group at ICFO has been involved in current European Space Agency (ESA) projects to develop a small footprint and low power consumption quantum transceiver and a high-flux entangled photon source.
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.
In our modern era of telecommunications and the Internet, information has become a valuable commodity. Sometimes it must therefore be protected against theft - in this case, loss of secret information to an eavesdropper. Most of today's transactions are protected using encryption unproven to be secure against a computational attack by a classical computer and, in fact, the standardly used encryption algorithms are provably vulnerable to the mind-boggling parallelism of a quantum computer, should one ever be physically realized. Enter quantum cryptography. Underlying nearly all forms of encryption is the necessity for a truly secret key, a random string of zeros and ones; the basic notion of quantum cryptography is to employ single photon transmissions (or the closest attainable approximation to these) to distribute the random key material, while removing the threat of an undetected eavesdropper. Now, nearly twenty years since the seminal quantum cryptography paper by Bennett and Brassard (Bennett C H and Brassard G 1984 Proc. IEEE Int. Conf. on Computers, Systems, and Signal Processing (Bangalore) (New York: IEEE) pp 175-9), we take a look at several state-of-the-art implementations, and glimpse how future quantum cryptosystems might look. We start with papers from three of the world's leading experimental quantum cryptography efforts: Stucki et al and Bethune and Risk describe working systems for quantum key distribution (QKD) over telecommunications fibres (at 1550 nanometres and 1300 nanometres, respectively). The former's achievement of quantum key exchange over 67 kilometres of optical fibre is a world record, as is the experimental demonstration by Hughes et al of daylight free-space QKD over a 10 km atmospheric range. Next, Lütkenhaus and Jahma explore the possible vulnerabilities of such systems (which employ attenuated laser pulses instead of actual single photon states) to conceivable future eavesdropping technologies. Enzer et al have implemented a totally new protocol, using polarization-entangled photons, which in some circumstances can tolerate higher error rates than the traditional one of Bennett and Brassard; moreover, the use of entanglement provides a means of `automatic source verification'. Finally, looking to the future, Elliott gives a provocative view of how these technologies may be merged into network operation, and Shapiro describes a method to combine a novel source of entangled photons with a means to transfer the photons' quantum state to trapped-atom quantum memories. If realized, these systems could presage the world's first quantum network. Focus on Quantum Cryptography Contents Quantum key distribution over 67 km with a plug&play system D Stucki, N Gisin, O Guinnard, G Ribordy and H Zbinden Autocompensating quantum cryptography Donald S Bethune and William P Risk Practical free-space quantum key distribution over 10 km in daylight and at night Richard J Hughes, Jane E Nordholt, Derek Derkacs and Charles G Peterson Quantum key distribution with realistic states: photon-number statistics in the photon-number splitting attack Norbert Lütkenhaus and Mika Jahma Entangled-photon six-state quantum cryptography Daphna G Enzer, Phillip G Hadley, Richard J Hughes, Charles G Peterson and Paul G Kwiat Building the quantum network Chip Elliott Architectures for long-distance quantum teleportation Jeffrey H Shapiro Ground to satellite secure key exchange using quantum cryptography J G Rarity, P R Tapster, P M Gorman and P Knight Method for decoupling error correction from privacy amplification Hoi-Kwong Lo Paul G Kwiat University of Illinois at Urbana-Champaign, USA
Quantum Key Distribution (QKD) is used in Quantum Cryptographic Systems to exchange secret key between parties who need to communicate secretly. Such a key can be used with a symmetric encryption schemes to establish a secure communication. Until recently, QKD is possible using optical fiber over few tens of kilometers but not more due to single photons getting absorbed by the fiber. There are no commercial wireless quantum crypto products yet, but QKD will soon be used in wireless medium from satellite to the earth so we could get 10,000 miles. But wireless medium brings its own problems. The energy transmitted via a wireless link spreads out, leading to higher and varying transmission losses, ambient daylight, or even light from the moon at night couple into the receiver, leading to a higher error rate. Interference from other photon sources air with clouds, dust and unsettled conditions creates intervention. In this paper, different techniques for communication in Quantum Cryptography using wireless networking infrastructure are discussed.