Cryptographic methods that do not use prime numbers?

Question

Does anyone know any cryptographic methods that do not use prime numbers? If so, which ones?

Answer 1

There is none. All cryptography involves the number 2, which is prime, whenever dealing with information in strings of bits—or in esoteric cases like ROT13, well, there's a prime number right there, 13, not to mention that 26, the size of the alphabet on which ROT13 works, is the product of primes 2 and 13.