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

From: Carlo Arenas <carenas@gmail.com>
Date: Nov 17, 2021, 03:36 UTC
Message-ID: <CAPUEsphh-enSYS66mi7_XaS0n1bmUvGXRcgVp6iqhg94xSHVog@mail.gmail.com>
In-Reply-To: <YZRxOrv9JFt2oeSU@coredump.intra.peff.net>

On Tue, Nov 16, 2021 at 7:04 PM Jeff King <peff@peff.net> wrote:

Show 12 quoted lines

>
> On Tue, Nov 16, 2021 at 05:50:44PM -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

I agree though that having a true random source will require the OS, but isn't it about generating 6 random letters?

Carlo