A quantum leap for cryptography

Blasting photons can create completely secure random keys

An international team of government, academic and commercial researchers has made significant strides in their quest to accelerate secure quantum cryptography. The group has devised a photon detector operating as much as 20 times faster than previously, making it possible to continuously generate and exchange cryptographic keys at up to 100 Mbps.

'This is a classic example of experiments from the physics lab being transitioned to a working technology,' said Jonathan Habif, a research scientist with BBN Technologies of Cambridge, Mass.

The equipment, built from off-the-shelf components, is running on the Defense Advanced Research Projects Agency's Quantum Key Distribution test bed network in Cambridge and Boston.

No eavesdropping

Quantum cryptography relies on the phase state of single photons'elemental particles of light'to generate secure cryptographic keys. A random series of photons representing ones or zeroes, depending on their spin and polarization, are streamed to a detector where they are used to create a key. Because the act of 'reading' a photon alters its state, the key cannot be detected by an eavesdropper. This makes feasible the rapid creation and distribution of one-time pads, considered the most secure type of cryptography.

A one-time pad is a list of random crypto keys shared by a sender and receiver. Because each key is random instead of being generated by a scheme known to both sender and receiver, it should be impossible to break a message encrypted using a one-time pad.

The trick is generating the keys quickly and distributing copies to the sender and receiver. But why go to the trouble of generating keys this way?

'Right now, the standard encryption schemes are good enough,' Habif said. 'But they're not based on a provable security model. Quantum cryptography is nice because it is provably secure.'

Computing power is advancing rapidly, which presents a double-edged sword because existing crypto schemes are based on computational complexity, said Robert Schwall, project leader in the quantum information and measurements project at the National Institute of Standards and Technology's Boulder, Colo., lab.

'The first guy who gets a quantum computer can read everybody else's mail,' Schwall said. 'You need a technology that is not vulnerable to that kind of computing. That's where quantum cryptography comes in,' because its security is based on the laws of quantum physics, not complexity.

The ability to rapidly generate and reset secure keys could make it possible to encrypt streaming video, said Carl Williams, chief of NIST's atomic physics division and coordinator of the quantum information program. Today this is possible only with low-resolution audio and video.

'I believe the next generation of products ... will have much more key material, but it still will not be fully mature,' Williams said. 'I think it is coming, but the cost per bit secured still is high.'

When exactly quantum cryptography moves past the early adopters and into the mainstream will depend on the type of information being secured as well as on the technology. When the risk from the loss of information passes the cost of the additional security, 'at that point, it will be viable,' Williams said.

At least one U.S. company, MagiQ Technologies Inc. of New York, will sell you a quantum cryptography system. But the tools are not quite ready for widespread adoption, said MagiQ CEO Robert Gelfond.

It works, but ...

'They primarily are still going through the testing process' with customers, Gelfond said. The QPN Security Gateway does what MagiQ says it will do, but it needs to do it more quickly, simply and robustly. 'It's more a question of reliability rather than operability.'

Common technology for detecting individual photons is slow and noisy compared with commercial networking equipment, Habif said. But scientists at the Moscow Institute of Physics, the University of Rochester and NIST modified a receiver used in radio astronomy to create the new photon detector now in use around Boston.

'This is a fundamentally new type of detector,' Habif said. 'The old one is solid state circuitry. This is superconducting technology.'

Tech on ice

The new detector uses a closed-cycle refrigerator to lower temperatures on the detector to 3 degrees Kelvin, near absolute zero. The system is housed in a rack-mounted unit and operates on the DARPA metro network linking BBN, Harvard University and Boston University at a continuous rate of 100 million pulses per second. It is believed the detector could scale up to 10 billion pulses a second.

'The refrigerator we are using is a commercial product, but it still is in development,' Habif said. 'Sadly, it is not very efficient, but it still runs off wall power.'

Gelfond sees the near-term market for quantum security in large enterprises and regulated businesses such as financial institutions.

'We think the biggest market will be the service provider market,' where network service providers will be able to offer quantum crypto links for an additional fee.

Quantum cryptography also will be attractive to users who have sensitive data that must be securely maintained for a long period of time. Although current schemes based on computational complexity are good enough for now, someone with enough time can wait for the computing power needed to break a key.

'Quantum cryptography is future proof,' Gelfond said. 'It is invulnerable to future advances in technology and algorithms.'

How urgent is the need for this next generation of cryptography? It depends on how fast technology moves. 'On the part of DARPA there is a real sense of urgency,' NIST's Schwall said. 'They want to be able to anticipate any breakthrough' that could antiquate current techniques.

About the Author

William Jackson is freelance writer and the author of the CyberEye blog.

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