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Quantum cryptography tackles video

06 May 2005

Video conferencing gets a security boost thanks to Toshiba Research Europe.

Toshiba Research Europe has used the science of quantum cryptography to transmit voice and video over a secure fiber link that is protected by the laws of physics. The demonstration is significant because it shows that the single-photon encryption technology is not only compatible with real Internet Protocol (IP) traffic but also robust enough for deployment on commercial fiber networks.

The system was shown to financial institutions and government representatives in London last week by scientists working at Toshiba’s Cambridge Research Laboratory.

Toshiba’s “Quantum Key Server” can generate up to 100 quantum (single-photon) keys per second, enough to encrypt each video frame with a separate key. In addition, it features an automatic management system that continually monitors and adjusts the system’s optical path length to allow it to operate continuously without any need for user intervention.

“We’ve demonstrated encrypted video because we wanted to show two things, first of all that we encrypt a large amount of information, and secondly that we can regularly change the encryption key,” said Andrew Shields, leader of Toshiba’s Quantum Information Group.

“We’ve also carried out some tests with the global communications provider MCI and seen that our system can operate on their network continuously for a month with no problems.”

Toshiba’s cryptography system operates at the telecoms wavelength of 1.55 µm over standard optical fiber. At the moment Toshiba uses heavily attenuated laser pulses to generate the quantum key and customized avalanche photodetectors to detect them. However, according to Shields the firm is now busy developing quantum-dot based LEDs and detectors that can generate and detect single photons.

"This technology [quantum dots] is not only potentially low cost but could also allow higher bit rates and longer fiber lengths,” Shields told Optics.org “We have prototypes devices for both and are now integrating them into our cryptography system, but it will 2-3 years before it is used routinely.”

Toshiba now plans to commercialise the system and is keen to talk to potential end-users. In 2003, the firm announced another world first when it succeeded in performing quantum cryptography over a distance of more than 100 km ( Cryptography breaks 100km barrier (June 2003)).

Communication with quantum cryptography is inherently secure because it takes advantage of the physical properties of single photons. In the technique, each transmitted bit of a cryptographic key is encoded upon a single photon.

The sender and recipient each have a key to decode the photon stream, but any attempt to hack into the link and capture the key is doomed to failure as it alters the quantum state of the intercepted photons. These changes are easily detectable, revealing the presence of the hacker.

Oliver Graydon is editor of Optics.org and Opto & Laser Europe magazine.

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