Bug#423902: apt should use both md5 and sha1

[Colin Watson <cjwatson@debian.org>]

On Mon, May 14, 2007 at 10:20:18PM +0200, Thomas Geyer wrote:
> Package: apt
> Version: 0.6.46.4
> Severity: wishlist
> 
> 
> Collisions for md5 and sha1 were found allready,
> so it's likely, that in the nearer future one of them alone won't be
> safe enough.
> 
> Since it is harder to find collisions for two checksums than for one,
> apt should use both of them at the same time for verifying packages.

This demonstrates a common misconception about hash algorithm, I'm
afraid. Search for "multicollisions" to find papers debunking the
usefulness of this technique. In short, concatenating MD5 and SHA1 adds
approximately six bits of security over using SHA1 alone, which is
unlikely to be worth the computational effort of doing so.

Cheers,

-- 
Colin Watson                                       [cjwatson@debian.org]