a program to delete duplicate files

[Jeff Shannon]

Patrick Useldinger wrote:

> David Eppstein wrote:
> 
>> When I've been talking about hashes, I've been assuming very strong 
>> cryptographic hashes, good enough that you can trust equal results to 
>> really be equal without having to verify by a comparison.
> 
> I am not an expert in this field. All I know is that MD5 and SHA1 can 
> create collisions. Are there stronger algorithms that do not? And, more 
> importantly, has it been *proved* that they do not?

I'm not an expert either, but I seem to remember reading recently 
that, while it's been proven that it's possible for SHA1 to have 
collisions, no actual collisions have been found.  Even if that's not 
completely correct, you're *far* more likely to be killed by a 
meteorite than to stumble across a SHA1 collision.  Heck, I'd expect 
that it's more likely for civilization to be destroyed by a 
dinosaur-killer-sized meteor.

With very few exceptions, if you're contorting yourself to avoid SHA1 
hash collisions, then you should also be wearing meteor-proof (and 
lightning-proof) armor everywhere you go.  (Those few exceptions would 
be cases where a malicious attacker stands to gain enough from 
constructing a single hash collision to make it worthwhile to invest a 
*large* number of petaflops of processing power.)  Sure it's not "100% 
perfect", but... how perfect do you *really* need?

Jeff Shannon