C# quickest two-way string shortening

Question

What is the quickest and best performance way to turn a string into a string of numbers and/or letters, then reverse engineer to the original string. Similar to turning a string into it's hash code, but that's a one-way conversion. I need a two-way method. I'm creating a simple url shorting service and I don't want to deal with a database.

I considered MD5 encrypting/decrypting via a private key, but I imagine there's another way that might be better on performance.

If encrypting/decrypting is the way to go, then which is the easiest on the processor?

Thanks!

Answer 1

When you encrypt you don't shorten anything. The cipher text is roughly the same length as the clear text. However, if you use a cryptographic hash you shorten the string to the length of hash. The drawback is that you are no longer able to reverse the hash back to the original string. I don't think you will be able to create a URL shortener using neither an encryption algorithm nor a cryptographic hash function. If that was possible to you could achieve infinite or at least very high compression of information.