Loophole found in quantum cryptography photon detectors


If you’re hoping to secure your data using quantum cryptography, you might want to find a shoulder to cry on.

Quantum cryptography ought to be 100 percent secure. In theory , it provides perfect security against eavesdroppers. But in practice, a number of loopholes have emerged (see here and here). And today, Vadim Makarov and pals at the Norwegian University of Science and Technology reveal another.

One crucial piece of kit that every quantum cryptographer needs is a detector capable of spotting single photons. And the detector of choice in about half of quantum cryptography experiments is the Perkin Elmer SPCM-AQR detector module. “Until recently, this has been the only commercially available Si single photon detector model,” say Makarov and buddies.

Sadly, it turns out to have a significant flaw. The Norwegian team says that bombarding the machine with bright optical pulses can override the control circuitry in a way that allows an eavesdropper to control its output. That gives Eve a way of staging a successful intercept attack.

I know what you’re thinking: why not switch to the gear used in the other half of quantum crypto experiments? The answer is that Makarov and pals have already shown that these devices have a vulnerability.

All is not lost, however. Now that the vulnerability has been revealed it should be straightforward to implement extra security to foil such an attack.

But the implications are clear. The eternal cat and mouse game between eavesdroppers and their victims looks set to continue. Which means that quantum cryptography may never be perfect.

Ref: arxiv.org/abs/0809.3408: Can Eve control PerkinElmer actively-quenched single-photon detector?

2 Responses to “Loophole found in quantum cryptography photon detectors”

  1. Norm says:

    This loophole was found only because they reverse-engineered the proprietary circuit in the PerkinElmer detector. Yet another example of how “security through obscurity” doesn’t work, except this time in the hardware world instead of the software world.

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