Scientists at Toshiba and Cambridge University have perfected a technique that offers a less expensive way to ensure the security of the high-speed fibre optic cables that are the backbone of the modern internet.
The research, published in the science journal Physical Review X, describes a technique for making tiny measurements needed to capture pulses of quantum light hidden in streams of billions of photons transmitted each second in data networks.
Scientists used an advanced photodetector to extract weak photons from the torrents of light pulses carried by fibre optic cables, making it possible to safely distribute secret keys necessary to scramble data over distances up to 90 kilometres.
Such data scrambling systems will most likely be used first for government communications systems for national security. But they will also be valuable for protecting financial data and ultimately all information transmitted over the internet.
The approach is based on quantum physics, which offers the ability to exchange information in a way that the act of eavesdropping on the communication would be immediately apparent. The achievement requires the ability to reliably measure a remarkably small window of time to capture a pulse of light, in this case lasting just 50 picoseconds - the time it takes light to travel 15 millimetres.
The secure exchange of encryption keys used to scramble and unscramble data is one of the most vexing aspects of modern cryptography.
Public key cryptography uses a key that is publicly distributed and a related secret key held privately, allowing two people who have never met to securely exchange information. But such systems are vulnerable to several things, including potentially to computers powerful enough to decode data protected by mathematical formulas.
If it is possible to reliably exchange secret keys, it is possible to use an encryption system known as a one-time pad, one of the most secure forms. Several commercially available quantum key distribution systems exist, but they rely on the necessity of transmitting the quantum key separately from communication data, frequently in a separate optical fibre, according to Andrew Shields, one of the authors of the paper and the assistant managing director for Toshiba Research Europe. This adds cost and complexity to the cryptography systems used to protect the high-speed information that flows over fibre optic networks.
Weaving quantum information into conventional networking data would lower the cost and simplify the task of coding and decoding the data, making quantum key distribution systems more attractive for commercial data networks, the authors said.
Despite their ability to carry prodigious amounts of data, fibre-optic cables are also highly insecure. An eavesdropper needs only to bend a cable and expose the fibre, Shields said. It is then possible to capture light that leaks from the cable and convert it into digital ones and zeros.