Darren New wrote:

>> Well... the fact that collisions can be constructed prove that they 
>> exist, which might suggest the function is "less random" than it 
>> should be...
> 
> First, yes, of course they exists. As soon as you have meesages >128 
> bits, you by necessity have collisions. Second, the function isn't 
> supposed to be random, it's supposed to be non-invertible.

Indeed. But I'm using it for its randomness...

> Hell, you're much more likely to get struck by lightning as you head 
> home from work than have an accidental collision in an MD5 hash.

Depends where you live. Apparently in the USA the chance of being killed 
by lightning is only 1 in 700,000. That's actually quite a *high* 
probability. o_O

Apparently the changes of winning the National Lottery (absurdly 
improbable) is x * 10^(-8), for some "small" x. (I don't remember what 
it is.) 2^(-128) works out as x * 10^(-39) - the theoretical probability 
of winning the Lottery several times back to back. I guess even if we 
assume MD5 is moderately screwed, you'd still have to estimate the 
collision probability at 10^(-24) or something. That's still fairly 
improbable...

>> The worrying thing being, how likely is it that such a thing might 
>> just happen by accident? :-}
> 
> Very slim, or it would have happened much earlier.

Yeah, I'm fairly sure it's quite a low probability too. I'd just like to 
be able to put an objective figure to it. ;-)

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