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Boffins: How to generate crypto-keys using a smartphone – and quantum physics

Would take '1018 times the age of the universe' to guess

Random numbers

Your smartphone can be used to generate cryptographic keys from truly random numbers "of a quantum origin", according to bods at the University of Geneva.

The Swiss research claims, quite simply, that illuminating the camera of a device like the Nokia N9 can cause quantum effects, which ultimately can be used to generate strong keys for encryption and decryption; in effect making the smartphone a quantum random number generator (QRNG).

That's a lot cheaper than the QRNG kit currently on offer – although it's more expensive than visiting the ANU's online QRNG site.

The attraction of using quantum effects is simple: quantum noise is truly random, and unlike pseudo-random number generators (PRNGs), they're not weakened by how the maths of PRNGs work. The trick is in the implementation – how quantum noise is detected, isolated, and digitised as a number, which is why QRNGs are expensive.

Until now, if the work presented in this Arxiv paper is borne out.

The authors say that smartphone CMOS cameras are now sensitive enough to take the place of expensive kit. “Their readout noise is of the order of a few electrons and their quantum efficiencies can achieve 80 per cent”, the paper states.

The University of Geneva quantum random number generator

The QRNG setup: quite simple if you have the right light source. Source: Arxiv

After running a characterisation test on the Nokia, the researchers generated random numbers by illuminating the cameras with the right number of photons needed to balance getting the maximum quantum uncertainty, while not saturating the detectors.

The researchers calculated that the resulting extracted bitstream was random enough that “it would take around 10118 trials “to notice a deviation from a perfectly random bit string.

“If everybody on earth used such a device constantly at 1Gbps, it would take 1080 times the age of the universe for one to notice a deviation from a perfectly random bit string.” ®

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