

Generating Unique Referrer Codes in PHP - hasitha
http://hasitha.posterous.com/generating-unique-referrer-codes-in-php

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bigiain
"There's a very real possibility that 2 completely different usernames could
result in the exact same md5 hash."

Errrmmm - no. Well, yes, but only where "real probability" equates to
something like a 1:10^18 chance of collision even after you've signed up every
human on the planet. An MD5 hash is 128 bits, or ~10^38 possible values. Even
considering the Birthday attack, there is no actual chance worth worrying
about of 2 MD5 hashes accidentally colliding. (See the table near at top of
<http://en.wikipedia.org/wiki/Birthday_attack> )

That doesn't mean MD5(username) is the right choice, but the reasoning in the
article about why not to use it is flawed.

