Abstract:A secure communication network with quantum key distribution in a metropolitan area is reported. Six different QKD systems are integrated into a mesh-type network. GHz-clocked QKD links enable us to demonstrate the world-first secure TV conferencing over a distance of 45km. The network includes a commercial QKD product for long-term stable operation, and application interface to secure mobile phones. Detection of an eavesdropper, rerouting into a secure path, and key relay via trusted nodes are demonstrated in this network. ©2011 Optical Society of AmericaOCIS codes: (270.5568) Quantum cryptography; (060.5565) Quantum communications. References and links1. N. Gisin, G. Ribordy, W. Tittel, and H. Zbinden, "Quantum cryptography," Rev. Mod. Phys. 74(1), 145-195 (2002). 2. V. Scarani, H. Bechmann-Pasquinucci, N. J. Cerf, M. Dušek, N. N. Lütkenhaus, and M. Peev, "The security of practical quantum key distribution," Rev. Mod. Phys. 81(3), 1301-1350 (2009

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In this paper, we report on the performance of the SwissQuantum quantum key distribution (QKD) network. The network was installed in the Geneva metropolitan area and run for more than one and a half years, from the end of March 2009 to the beginning of January 2011. The main goal of this experiment was to test the reliability of the quantum layer over a long period of time in a production environment. A key management layer has been developed to manage the key between the three nodes of the network. This QKD-secure network was used by end-users through an application layer.PACS numbers: 03.67.Dd, 03.67.Hk, ‡ D Stucki and M Legré contributed equivalently to the writing of this paper.

We present a compactly integrated, 625 MHz clocked coherent one-way quantum key distribution system which continuously distributes secret keys over an optical fibre link. To support high secret key rates, we implemented a fast hardware key distillation engine which allows for key distillation rates up to 4 Mbps in real time. The system employs wavelength multiplexing in order to run over only a single optical fibre. Using fast gated InGaAs single photon detectors, we reliably distribute secret keys with a rate above 21 kbps over 25 km of optical fibre. We optimized the system considering a security analysis that respects finite-keysize effects, authentication costs and system errors for a security parameter of ε QKD = 4 × 10 −9 .

The security of quantum communication using a weak coherent source requires an accurate knowledge of the source's mean photon number. Finite calibration precision or an active manipulation by an attacker may cause the actual emitted photon number to deviate from the known value. We model effects of this deviation on the security of three quantum communication protocols: the Bennett-Brassard 1984 (BB84) quantum key distribution (QKD) protocol without decoy states, Scarani-Acín-Ribordy-Gisin 2004 (SARG04) QKD protocol, and a coin-tossing protocol. For QKD, we model both a strong attack using technology possible in principle, and a realistic attack bounded by today's technology. To maintain the mean photon number in two-way systems, such as plugand-play and relativistic quantum cryptography schemes, bright pulse energy incoming from the communication channel must be monitored. Implementation of a monitoring detector has largely been ignored so far, except for ID Quantique's commercial QKD system Clavis2. We scrutinize this implementation for security problems, and show that designing a hack-proof pulse-energy-measuring detector is far from trivial. Indeed the first implementation has three serious flaws confirmed experimentally, each of which may be exploited in a cleverly constructed Trojan-horse attack. We discuss requirements for a loophole-free implementation of the monitoring detector.