[gibybo]

Yes, nothing to do with prime numbers. SHA-2 uses some constants. A lot of cryptography needs constants for various reasons. There is always some concern that the creator chose specific constants that weaken or give them a backdoor to the crypto scheme. To reduce this concern, they often choose constants from some simple mathematical basis, perhaps the numbers '1234567890', or digits of pi, etc. In SHA-2's case, they used the first 32 bits of the fractional parts of the square roots of the first n primes.

The numbers they use are not primes, nor are primes useful in any way for attacking SHA. The algorithm still has nothing to do with prime numbers.