encryption-symmetric

I need an algorithm that can do a one-to-one mapping (ie. no collision) of a 32-bit signed integer onto another 32-bit signed integer. My real concern is enough entropy so that the output of the function appears to be random. Basically I am looking for a cipher similar to XOR Cipher but that can generate more arbitrary-looking outputs. Security is not my real concern, although obscurity is. Edit for clarification purpose: The algorithm must be symetric, so that I can reverse the operation without a keypair. The algorithm must be bijective, every 32-bit input number must generate a 32-bit

I'm trying to encrypt some (cookie) data in C# and then decrypt it in PHP. I have chosen to use Rijndael encryption. I've almost got it working, except only part of the text is decrypted! I started working from this example: Decrypt PHP encrypted string in C# Here's the text (JSON) that I am encrypting (sensitive information removed): {"DisplayName":"xxx", "Username": "yyy", "EmailAddress":"zzz"} So I login to the C# app which creates/encodes the cookie from stored Key and IV and then redirects to the PHP app which is supposed to decrypt/read the cookie. When I decrypt the cookie, it comes out