Sunday, June 10, 2007


“Unbreakable” encryption works in real time over long distances, NIST says

‘They say they have built a prototype high-speed quantum key distribution (QKD) system that can perform a theoretically unbreakable “one-time pad” encryption, transmission and decryption of a video signal in real-time over a distance of at least 10 kilometers. [..]

One important requirement for any candidate system is that it be compatible with existing fiber-optic telecom networks that transmit at wavelengths of either 1550 or 1310 nanometers (nm) to reach the greatest distance. Another requirement is a highly efficient photon detector that can detect single photons reliably without introducing significant amounts of “noise.” One of the best low-noise detectors, a silicon-based avalanche photo diode (Si-APD), does not function at the telecom wavelengths. Instead, it operates best at much shorter wavelengths around 700 nm. To take advantage of the Si-APD, the NIST group designed a sub-system to “up-convert” single photons from a transmission wavelength of 1310 nm to 710 nm for high-efficiency detection.’

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