Re: [RFC] adding support for md5

From: Johannes Schindelin <johannes.schindelin@gmx.de>
Date: Aug 18, 2006, 11:37 UTC
Message-ID: <Pine.LNX.4.63.0608181330210.28360@wbgn013.biozentrum.uni-wuerzburg.de>
In-Reply-To: <44E5A416.9040709@sinister.cz>

Hi,

On Fri, 18 Aug 2006, Trekie wrote:

Show 9 quoted lines

> Johannes Schindelin wrote:
> > SHA1 has been broken (collisions have been found):
> > 
> > http://www.schneier.com/blog/archives/2005/02/sha1_broken.html
> 
> I don't think you're right. That blog just says, that Wang can find
> 
> "collisions in the the full SHA-1 in 2**69 hash operations, much less
> than the brute-force attack of 2**80 operations based on the hash length."

True. I have not heard of a collision either.

> The point is why use MD5 if anyone can compute a collision?

It does not suffice to generate collisions to make a hash unusable for our purposes: you would have to find a way to produce another text for a _given_ hash. Plus, this text would not only have to look meaningful, but compile. And preferrably introduce a back door.

Granted, once people find out how to generate another text, they can try to "optimize" some block between "/*" and "*/", so that the hash stays the same. But AFAICT none of the breaks of SHA1 or MD5 point into such a direction. Yet.

But _even if_ somebody succeeds in all that, that somebody has to convince _you_ to pull. And if you already have that object (the "good" version), it will not get overwritten.

Ciao, Dscho