One of the great unsolved problems in Mathematics is the
Riemann hypothesis. Riemann came up with an exact way to show how many primes you'd count if you examined every number up to a number x.
(The prime counting function). Since public key encryption depends on finding the prime factors of a huge number a proof of the Riemann hypothesis would open a giant wedge into this method of encryption. It's been unproved for over 150 years and if anyone does prove it they are eligible for a one million dollar reward.
> Since public key encryption depends on finding the prime factors of a huge number
You may want to restate this for those who don’t understand that ciphers that use this technique, not public key encryption in general, is what would be affected here.