Eavesdropper Steals Quantum Crypto Keys

The research group's eavesdropping of quantum cryptography key generation systems didn't happen overnight. The group began its research in 2007, when members started testing how common, single photon detectors react to bright light. In July 2009, the group conducted experiments, in which it found that its eavesdropper, dubbed Eve, could eavesdrop on its receiver, dubbed Bob, without Bob knowing.

Later, the team found that commercial quantum cryptography systems could likely be compromised in the same manner. They detailed those findings last year, in a paper published by Nature Photonics. This latest research, however, actually demonstrated the attack in a practical setting, against a fully deployed research system. Going forward, the research team hopes to build the "perfect countermeasure" to the attack.

How useful is quantum cryptography for key generation purposes?

Security expert Bruce Schneier, chief security technology officer of BT, has called it "unbelievably cool, in theory, and nearly useless in real life," because he sees no commercial value. "It's not that quantum cryptography might be insecure; it's that cryptography is already sufficiently secure," he said.

Makarov, however, disputes Schneier's conclusions. First, he said, quantum cryptography provides a way to encrypt information indefinitely, despite advances in traditional cryptography. "If one wants to protect today's secrets from future advances in cryptanalysis, quantum cryptography offers a solution," he said. "Advances that compromise classical cryptography can happen with little warning, and then an attacker who recorded today's classically encrypted secrets can crack them open retroactively. In contrast, today's quantum cryptography cannot be eavesdropped by a future technology."

For example, encrypted network links currently also provide a single point of failure for attackers to exploit, especially given the difficulty of accessing physically secured data centers. "The backbone link and its encryption already cost the organization a lot," he said. "Does it make sense to add another layer of security insurance to this potential single point of failure, by adding quantum key distribution, in addition to the classical key distribution, at a comparatively small extra cost? I certainly think so."

Today's commercial cryptography key generation systems combine traditional key generation with quantum cryptography key generation. Accordingly, they cost more than traditional systems alone. So, when would you use the technology? Typically, it's most useful for "applications where you have very critical data, or data with a very long lifetime," said Ribordy, because as noted, the data can't be decrypted by some future code-breaking technology. "We have commercial customers that have decided to deploy this technology, because they've decided they need the additional security."

Quantum cryptography does face some limits. For starters, it only works with fiber optic networks. ID Quantique's Ribordy also said that commercial quantum cryptography key generation systems currently have a range of about 100 kilometers (62 miles), although the world record--achieved in the lab--is about 250 kilometers (155 miles). Currently, as distance increases, bitrate decreases. The "holy grail" in the future, he said, would be quantum repeaters, able to maintain bitrates over any distance.

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