China Researchers Develop a Quantum Cryptography Network for Secure Local Government Communications

Security of Internet communications and online financial transactions rests upon the complexity of the underlying cipher algorithms that encrypt secure traffic. But as the possibilities of quantum computing become more real - which may in the not too distant future putting the equivalent of today's super-computer into a laptop - we've begun to realize that today's secure communications my not remain so secure in the years ahead, not when met with a fantastic leap in computing power.

Even now, with the advent of cloud or distributed computing and specific hacking chips, the continued security of traditional encryption becomes ever more uncertain.

The solution, according to some cipher experts, is to be found in what is dubbed quantum cryptography, or quantum key distribution. This uses principles of quantum mechanics to guarantee secure communication by enabling two parties to produce a shared random bit string known only to them. This can then be used as a key to encrypt and decrypt messages.

Quantum communication involves encoding information in quantum states, or qubits, as opposed to classical communication's use of bits. Usually, photons are used for these quantum states. Quantum cryptography exploits certain properties of these quantum states to ensure its security using several different possible approaches.

Without belaboring the finer technical details here, quantum cryptography harness principles of fundamental physics for its security rather than assumptions about the computer power resources available to a potential adversary. Combined with the quantum key distribution (QKD) and the "one-time pad" algorithm, quantum cryptography can establish unconditional secure communication between legal users, for now and the future.

According to a report in the Chinese Science Bulletin, the Key Laboratory of Quantum Information (CAS), University of Science and Technology of China has recently demonstrated a metropolitan Quantum Cryptography Network (QCN) for government administration in Wuhu, China.

Compared with prior network archetectures, the new network offers a whole new level of security. Wuhu QCN implements a hierarchical structure with multi-levels of security based on three different networking approaches. Nodes with different priorities and demands are set in the central backbone net or the subnet, and choose which networking technique to use for which messages. All the QKD links are based on the BB84 protocol with decoy state which offers a significant level of security. Meanwhile, QKD software that all nodes run, application programs for encrypting text messages, sound and video are developed as well.

Fang-xing Xu and he co-authors note in their paper: "In the process of QKD industrialization, the stability of the QKD system and the networking techniques are two heavy cruxes."

And they add that the Wuhu QCN implements the Faraday-Michelson Interferometer (FMI) system, an unidirectional QKD scheme with the strict proof of its security and stability which can auto-compensate the influence of the birefringence in the transmitting channel that will jeopardize the performance of QKD system. Several field demonstrations of KLQI group including Beijing-Tianjin QKD experiment (2004), four-port star type network in Beijing (2007) and the Wuhu quantum cryptography network for Government administration (2009) clearly show that the stability and robustness of this QKD basic device is sufficient for practical implementations.

A press statement, issued today, offers further technical details: "Networking is a milestone for the popularization of quantum cryptography service," it stated. "However, the no-clone theorem of quantum system makes data traffic difficult to route in the net while guaranteeing the security of the protocol. The Wuhu cryptography network assembles the widely-used techniques of quantum router, active optical switch routing and trusted relay to construct a hierarchical and extendable structure. A full-mesh backbone network is built with a quantum router in the center to supply a no-congestion communication between all the gateways simultaneously, while the quantum switch based on the time multiplexing can achieve a balance for subnets between network efficiency and speed. In addition, trusted relay is