Quantum 'sealed envelope' system enables 'perfectly secure' information storage

November 4, 2013
Credit: Paul Hocksenar

A breakthrough in quantum cryptography demonstrates that information can be encrypted and then decrypted with complete security using the combined power of quantum theory and relativity - allowing the sender to dictate the unveiling of coded information without any possibility of intrusion or manipulation.

Scientists sent encrypted data between pairs of sites in Geneva and Singapore, kept "perfectly secure" for fifteen milliseconds - putting into practice what cryptographers call a 'bit ' protocol, based on theoretical work by study co-author Dr Adrian Kent, from Cambridge's Department of Applied Mathematics and Theoretical Physics.

Researchers describe it as the first step towards impregnable information networks controlled by "the combined power of Einstein's relativity and " which might one day, for example, revolutionise financial trading and other markets across the world.

'Bit commitment' is a mathematical version of a securely sealed envelope. Data are delivered from party A to party B in a locked state that cannot be changed once sent and can only be revealed when party A provides the key – with security guaranteed, even if either of the parties tries to cheat.

The technique could one day be used for everything from global financial trading to secure voting and even long-distance gambling, although researchers point out that this is the "very first step into new territory".

This is a significant breakthrough in the world of 'quantum cryptography' – one that was once believed to be impossible. The results are published in the journal Physical Review Letters.

"This is the first time perfectly secure bit commitment – relying on the laws of and nothing else – has been demonstrated," said Adrian Kent.

"It is immensely satisfying to see these theoretical ideas at last made practical thanks to the ingenuity of all the theorists and experimenters in this collaboration."

Any signal between Geneva and Singapore takes at least fifteen milliseconds – with a millisecond equal to a thousandth of a second. This blink-of-an-eye is long enough with current technology to allow data to be handed over encrypted at both sites, and later decrypted – with security "unconditionally guaranteed" by the laws of physics, say the team.

The researchers have exploited two different areas of physics: Einstein's special relativity – which interprets uniform motion between two objects moving at relative speeds – combined with the power of quantum theory, the new physics of the subatomic world that Einstein famously dismissed as "spooky".

Completely secure 'bit commitment' using quantum theory alone is known to be impossible, say researchers, and the "extra control" provided by relativity is crucial.

Professor Gilles Brassard FRS of the Universit'e de Montr'eal, one of the co-inventors of quantum cryptography who was not involved in this study, spoke of the "vision" he had fifteen years ago - when trying to combine quantum 'bit commitment' with relativity to "save" the theory - in which Einstein and early quantum physicist Niels Bohr "rise from their graves and shake hands at last":

"Alas, my idea at the time was flawed. I am so thrilled to see this dream finally come true, not only in theory but also as a beautiful experiment!" he said.

Bit commitment is a building block – what researchers call a "primitive" – that can be put together in lots of ways to achieve increasingly complex tasks, they say. "I see this as the first step towards a global network of information controlled by the combined power of and quantum theory," Kent said.

One possible future use of relativistic could be global stock markets and other trading networks. It might be a way of leveling the technological 'arms race' in which traders acquire and exploit information as fast as possible, the team suggest, although they stress at such an early stage these suggestions are speculative.

The new study builds on previous experiments that, while successful, had to assume limitations in the technology of one or both parties – and consequently not entirely "safe or satisfactory" says Kent, "since you never really know what technology is out there".

Explore further: Yale scientist sheds fresh light on Einstein

More information: prl.aps.org/abstract/PRL/v111/i18/e180504

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3 / 5 (2) Nov 04, 2013
As with all technology I see some good aspects and some that will prove difficult.

A completely secure network for fanatics to communicate with will make it more difficult to prevent violence and to apprehend them.

OTOH with the recent egregious abuses of power by the American and UK governments I see some very desirable aspects to the technology as well.
not rated yet Nov 04, 2013
Knowing there is no privacy, that someone could be listening in at any time, can create fanatics and fuel existing ones.
It will be abused, as is everything, but maybe having one part of our lives that isn't controlled and monitored, some good old fashioned privacy, will go a long way to reducing fanaticism.
5 / 5 (1) Nov 04, 2013
Unfortunately the article only talks about what it could be used for and not how it actually works. (And the abstract linked at the bottom is only a little more enlightening)

Anyone have a clue what this is about? I'm clear on what a commitment protocol is, but where the relativistic part comes in eludes me.
not rated yet Nov 04, 2013
Anyone have a clue what this is about? I'm clear on what a commitment protocol is, but where the relativistic part comes in eludes me.

Alright, keep in mind that I'm not a cryptographer or a physics expert, just an enthusiast.
You know what bit commitment is, so you know Alice and Bob can't cheat. However, the protocols don't do anything about Eve listening in and raise the question of the shared key being cracked. In standard cryptography, anything short of a one time pad can be cracked.

With quantum cryptography, not only is the key unbreakable (it is related to the superposition state of the information) but Eve is cut out because any attempt to listen in on the channel breaks the entanglement and renders the channel just so much noise...

...but I have a feeling that's too basic for you, AA, so I don't think I quite understand your question.
not rated yet Nov 04, 2013
but Eve is cut out because any attempt to listen in on the channel breaks the entanglement and renders the channel just so much noise...

That's also the case for regular quantum key exchange systems (which have been published and already been broken - though by cleverly exploiting inadequacies in the hardware and not the QM principle behind it).

I was wondering what makes this particular approach more secure. Commitment protocols aren't 100% secure (though they can be made arbitrarily secure. As you point out: only OTPs are totally secure. But they require a trusted/secure exchange of keys which is a rather major disadvantage)

I'm wondering where the relativity as noted here:
using the combined power of quantum theory and relativity
comes into play. How do they use the knowledge of the relative motion of sender and receiver to secure the transmission?

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