RE: [PATCH 1/2] wrapper: add a helper to generate numbers from a CSPRNG

> On Tue, Nov 16, 2021 at 07:36:51PM -0800, Carlo Arenas wrote:
> 
> > > > for the little amount of random data we need, it might be wiser to
> > > > fallback to something POSIX like lrand48 which is most likely to
> > > > be available, but of course your tests that consume lots of random
> > > > data will need to change.
> > >
> > > Unfortunately that won't help. You have to seed lrand48 with
> > > something, which usually means pid and/or timestamp. Which are
> > > predictable to an attacker, which was the start of the whole
> > > conversation. You really need _some_ source of entropy, and only the OS
> can provide that.
> >
> > again, showing my ignorance here; but that "something" doesn't need to
> > be guessable externally; ex: git add could use as seed contents from
> > the file that is adding, or even better mix it up with the other
> > sources as a poor man's /dev/urandom
> 
> Those contents are still predictable. So you've made the attacker's job a little
> harder (now they have to block tempfiles for, say, each tag you're going to
> verify), but haven't changed the fundamental problem.
> 
> It definitely would help in _some_ threat models, but I think we should strive
> for a solution that can be explained clearly as "nobody can DoS your
> tempfiles" without complicated qualifications.