I feel like I should comment some of the clams being posted as replies here. For starters, speed IS an issue with MD5 in particular and also SHA1. I've written my own MD5 bruteforce application just for the fun of it, and using only my CPU I can easily check a hash against about 200mill. hash per second. The main reason for this speed is that you for most attempts can bypass 19 out of 64 steps in