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

Would not this amount to a Block Cipher of block size = 32 bits ?

Not very popular, because it's easy to break. But theorically feasible. Here is one implementation in Perl : http://metacpan.org/pod/Crypt::Skip32

UPDATE: See also Format preserving encryption

UPDATE 2: RC5 supports 32-64-128 bits for its block size