One-Time-Pads are the absolute best way of doing encryption, at the expense of requiring a key exactly as long as the message. This makes it impossible to send the key securely, because we would have to go back to square one with the key now being the new message. Even if we could physically meet and swap hard drives of pre-made keys we would need to trust that the keys are fresh and haven't been copied elsewhere. Ideally, we would need a device that is nearly impossible to clone and that could generate on the spot a large amount of keys in a reliable manner. The team lead by Amy Foster at Johns Hopkins University developed exactly that device. It is a nonlinear photonic crystal disk with an input and an output waveguide, which scambles the input chaotically but very reproducibly. This means that the key depends on the input, which we can choose at will. The amount of random keys that we can extract by using all the combinations of input patterns is up to 2.4 Gb per disk, but considering its dimensions (about 30 micrometers), the density per area is a thousand times larger than the best current commercial storage solutions. To investigate clonability, the team built identical copies of each device, even physically next to each other to minimize differences in the material, but even so they were unsuccessful at decrypting a message using a cloned device. This solution might one day enable an almost unconditional security of our personal communications.
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