Hi,

> In preparation for a talk I'm going to give, I wanted
> to estimate how good 128 bits MD5 hashes were: how many
> hashes must be taken before the probability for a collision
> become non negligible? (I'm assuming equi-probability of
> every hash.)

I reckon that by saying "how good 128 bits MD5 hashes were"
you are aware of the recent attacks that make MD5's effective
security less than 128-bit.  The Wikipedia has a good summary:
http://en.wikipedia.org/wiki/MD5

Cheers,
Dario Teixeira