If you’ve got a secret to keep safe, look to the skies. Physicists have proposed using the afterglow of the big bang to make encryption keys.

The security of many encryption methods relies on generating large random numbers to act as keys to encrypt or decipher information. Computers can spawn these keys with certain algorithms, but they aren’t truly random, so another computer armed with the same algorithm could potentially duplicate the key.

An alternative is to rely on physical randomness, like the thermal noise on a chip or the timing of a user’s keystrokes.

Now Jeffrey Lee and Gerald Cleaver at Baylor University in Waco, Texas, have taken that to the ultimate extreme by looking at the cosmic microwave background (CMB), the thermal radiation left over from the big bang.

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