Seperating encoding from decoding

Hi,
I'm looking for a system which detaches the decoding process from the encoding process. That is, I would like a system for encoding data, but even if both the encoded data and the encoding process is known I would like it to be possible to decode the data with a seperate algorithm.

I realise I didn't explain that very well so I'll say what I want to use it for. On a website I want to store details and for them to be encoded, since this means both encoded data and the encoding system are at risk of discovery by hacking this means it's not very safe. I would like it so that even with both of those, it is either impossible or very hard to crack the data, but for ourselves to have a standalone system to decode it with.

Is this even possible, or is it inherently impossible by way that the encoding process is always directly linked to the decoding process?

re: Seperating encoding from decoding

do you mean something like public key encryption (RSA)?

re: Seperating encoding from decoding

I believe that's what I'm after, thank you. I will look into it, do you know how hard it is to calculate a decryption key from the encryption key and encrypted data? How possible is it, and how would I go about making it more difficult?

re: Seperating encoding from decoding

depending on the key length, got to be difficult above 256 bit. there's quite a lot of info about cryptography in wikipedia