From: "Iñaki Baz Castillo" <ibc@...>
Date: 2012-12-20T18:08:37+09:00
Subject: Efficient way to encode a string with a secret string and recover it

Hi, basically I receive a string generated by a user, then "encode" it
using some secret string I own and pass the result to other user, and
when I receive such a resulting string I must be able to decode it
using my secret string (but no other should be able to decode the
resulting string without knowing my secret key. This is:


original_string = "test"

secret_key = "ABCD"

modified_string = HASH_FUNCTION(original_string, secret_key)

original_string = UNHASH_FUNCTION(modified_string, secret_key)


Any suggestion for the above HASH_FUNCTION and UNHASH_FUNCTION? I
would like it to be something really efficient.

Thanks a lot.

-- 
Iñaki Baz Castillo
<ibc@aliax.net>