Discovery slashes quantum crypto costs

Discovery slashes quantum crypto costs
Discovery slashes quantum crypto costs 

By Matthew Broersma
03 June 2008

Researchers at the US National Institute of Standards and Technology 
(NIST) have demonstrated a technique that could make quantum 
cryptography significantly cheaper to implement, moving it nearer to 
possible commercial acceptance.

The technique, outlined in a paper to be published this month in the 
journal IEEE Communications Letters, is aimed at cutting the cost of 
equipment needed for quantum key distribution (QKD), designed to 
distribute cryptographic keys using a secure system based on the 
principles of quantum mechanics.

Such systems are typically based on the distribution of photons through 
a fibre-optic network, with information encoded in the polarisation of 
the photons.

They are designed to allow an absolute level of security, wth any 
attempt to monitor the system by a third party, for instance, 
necessarily disrupting the system.

However, such systems are expensive to implement, with the most common 
polarisation-based protocol, known as BB84, requiring four single-photon 
detectors, costing $5,000 (2,500) to $20,000 (10,000) each, the NIST 

The new method, called detector-time-bin-shift (DTBS), shifts photons 
into two distinct "time bins".

This means a set of two detectors can be used to sequentially record the 
two sets of photons, rather than requiring four detectors to 
simultaneously record all the photons, the NIST said.

In their work on a protocol called B92, the researchers reduced the 
required number of detectors from two to one, the NIST said.

Further work carried out since the completion of this month's paper 
further reduced the number of photon detectors needed for the BB84 
protocol from four to one, the NIST said.

The arrangement detailed in the paper cuts transmission rates by half, 
but the NIST system still works at broadband speeds, it said. The 
organisation said its experimental network can encrypt and decrypt 
webcam-quality video streams in real time using DTBS.

In 2006 the NIST managed to shift quantum-encrypted information at a 
"raw" throughput of 4 million bits per second across a 1 km-long fiber 

This was at least twice NIST's previous record, which has been rising 
since the agency announced it had broken the 1 million bits per second 
barrier in May 2004. At such transfer rates, it becomes practical to use 
QKD cryptography to secure a video stream.

In 2005 Toshiba Europe reached the demonstration phase of what it 
claimed was the first system to use quantum cryptography to secure a 
real-time video and voice data stream, developed by a 30-person team of 
scientists working at the company's Cambridge Research Laboratory.

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