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A "time cloak" that conceals events rather than objects can hide secret messages through a trick of light, making information invisible to all but the intended recipient.

Like an invisibility cloak that makes something disappear in plain sight, a time cloak makes an event disappear in time. It works by manipulating light traveling along an optical fibre.

Imagine a row of cars speeding along a road slowing down in concert to create brief paths for pedestrians to safely cross. When the cars that let the pedestrians cross ahead of them speed up and re-join the rest of the traffic, no one can tell there was ever a gap in the flow – the pedestrians' presence has been cloaked.

In the same way, photons' paths can be tweaked to create brief gaps where information can safely hide.

Last year, a team at Purdue University in Indiana built a cloak that could transfer hidden data at 1.5 gigabits a second, fast enough to make it theoretically useful for real communication. The only thing was, the message was hidden so well that no one could actually read it. That problem has now been solved.

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