TIL That primes numbers used in cryptography aren't 100% primes. They are numbers that has a false positive rate of less than one in a million billion billion of not being primes.

https://en.wikipedia.org/wiki/Miller%E2%80%93Rabin_primality_test

https://www.reddit.com/r/todayilearned/comments/1565541/til_that_primes_numbers_used_in_cryptography/