Shorten String or encode/decode a string

I want to shorten a string that I'll be throwing through the url. It's not so much that it's too long, but it's ugly. What it is, is my query string that I need to pass through to different pages, i.e. viewing multiple pages. Anyway, I was looking at encode and decode features but not really sure that they could shorten it down significantly. Now I understand that I won't be able to use it, but I tried the crypt() function and liked how small it made it. The string information doesn't need to be secure in anyway, just smaller (and look like nothing understandable would be good also).