Simple integer encryption

Question

Is there a simple algorithm to encrypt integers? That is, a function E(i,k) that accepts an n-bit integer and a key (of any type) and produces another, unrelated n-bit integ

Answer 1

You could take an n-bit hash of your key (assuming it's private) and XOR that hash with the original integer to encrypt, and with the encrypted integer to decrypt.

Probably not cryptographically solid, but depending on your requirements, may be sufficient.