Re: Let's shrink Packages.xz

[Jakub Wilk <jwilk@debian.org>]

* Peter Palfrader <weasel@debian.org>, 2014-07-14, 20:25:
> > The basic idea is that it's much harder to come up with a 
> > simultaneoush hash collision with both SHA-1 and SHA-2 than breaking 
> > either of them independently.
>
> ISTR reading papers that put this "much harder" into doubt.  But I 
> can't find those references, alas.

You might have had this paper in mind:
https://www.iacr.org/archive/crypto2004/31520306/multicollisions.pdf
Quoting §4: “If F and G are good iterated hash functions with no attack 
better than the generic birthday paradox attack, we claim that the hash 
function F||G obtained by concatenating F and G is not really more secure 
that F or G by itself.”

--
Jakub Wilk