title: substr md5 collision
body: <p>I need a 4-character hash. At the moment I am taking the first 4 characters of a <code>md5()</code> hash. I am hashing a string which is 80 characters long or less. Will this lead to collision? or, what is the chance of collision, assuming I'll hash less than 65,536 (16<sup>4</sup>) different elements?</p>