How does the CI forum do this?

[eluser]megabyte[/eluser]
If I search in this forum, I get a url such as this:

http://ellislab.com/forums/search_result...f865d71b4/


Now no matter what I search for the encoded segment is always the same length.

Is this a 2 way encoded string?

If so does anyone know how they do this?

I've searched but everything I could find encrypts to a variable length.


Thanks.