Really Random Numbers

Apr 12, 2018
Originally published on May 3, 2018 11:42 am
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A team of physicists has come up with a way to secure communications over the Internet, which is not a small deal in this day and age. Their approach involves creating truly random numbers. NPR's Joe Palca has the story.

JOE PALCA, BYLINE: It's not hard to come up with an example of why randomness is key to online security. Peter Bierhorst is a mathematician at the National Institute of Standards and Technology in Boulder, Colo.

PETER BIERHORST: Suppose you're logging into your bank's website from a computer, and it says, we don't recognize this computer; can we send you a six-digit, little one-time PIN through a text message? And then type it into your computer, and then we'll know it's you.

PALCA: Now, with a six-digit PIN, if each digit is picked randomly, the chance of someone guessing the PIN on the first try is one in a million. But what if the PIN the bank sends is not really random?


Pi is known as an irrational number. It has an infinite number of digits. Bierhorst says, suppose you took six digits from pi.

BIERHORST: That would look pretty unpatterned. But if you had some adversary, and they started figuring out what the bank was doing, which was just using the digits of pi in sequence one after the other for all of these little PINs, then that adversary would pretty soon figure that out and be able to hack into your secure communication with the bank.

PALCA: So truly random numbers are what you need to assure as much security as possible. To get such numbers, Bierhorst and his colleagues turned to the weird and wonderful world of quantum physics. As they report in the journal Nature, the researchers used particles of light known as photons to test for randomness.

BIERHORST: The way we set this experiment up is very subtle.

PALCA: Without going into too much detail, the experiment made measurements of the photons that had been joined in a spooky physical state known as quantum entanglement. The measurements were made far enough apart so that the speed of light could not have affected the outcome.

BIERHORST: And so if you don't believe that signaling faster than the speed of light is possible, you have to accept the random character in our measurement outcomes.

PALCA: Bierhorst says now that they are sure their photon measurements are truly random, they plan to use the setup as a random number generator. Umesh Vazirani works with quantum physics at the University of California, Berkeley. He says Bierhorst and his colleagues aren't the first to try to use quantum physics to generate random numbers.

UMESH VAZIRANI: It's such a surprise. In a classical world, you could never, ever certify something as random. It's something that the quantum world allows us to do.

PALCA: The quantum world may allow us to do many more things, such as make unspeakably fast computers. But that's a story for another day. Joe Palca, NPR News.


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