Re: is "premature next" a real world rng concern, or just an academic exercise?

From: Dominik Brodowski <linux@dominikbrodowski.net>
To: "Jason A. Donenfeld" <Jason@zx2c4.com>
Cc: Thomas Ristenpart <ristenpart@cornell.edu>,
	Yevgeniy Dodis <dodis@cs.nyu.edu>, tytso <tytso@mit.edu>,
	Nadia Heninger <nadiah@cs.ucsd.edu>,
	Noah Stephens-Dawidowitz <noahsd@gmail.com>,
	Stefano Tessaro <tessaro@cs.washington.edu>,
	"torvalds@linux-foundation.org" <torvalds@linux-foundation.org>,
	"D. J. Bernstein" <djb@cr.yp.to>,
	"jeanphilippe.aumasson@gmail.com"
	<jeanphilippe.aumasson@gmail.com>,
	"jann@thejh.net" <jann@thejh.net>,
	"keescook@chromium.org" <keescook@chromium.org>,
	"gregkh@linuxfoundation.org" <gregkh@linuxfoundation.org>,
	Peter Schwabe <peter@cryptojedi.org>,
	"linux-crypto@vger.kernel.org" <linux-crypto@vger.kernel.org>,
	"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: is "premature next" a real world rng concern, or just an academic exercise?
Date: Fri, 13 May 2022 08:19:13 +0200	[thread overview]
Message-ID: <Yn34YWhH1nSa8O8K@owl.dominikbrodowski.net> (raw)
In-Reply-To: <YnzzuuLPssc3/tVe@zx2c4.com>

Am Thu, May 12, 2022 at 01:47:06PM +0200 schrieb Jason A. Donenfeld:
> But on the other hand, it appears that none of us really thinks that
> premature next is a real problem worth complicating designs over. So
> maybe we can just say that it is nice when the silicon in one way or
> another helps with premature next, but maybe not an explicit must have.
> So where does that leave us?
> 
> - Systems with RDSEED/RDRAND don't have premature next, due to the above
>   KDF salt. This is probably the majority of systems out there these
>   days. This also applies to the sleep resumption notification (and the
>   vmgenid one), and I suspect that most systems with S3 or S0ix or
>   whatever else these days also probably have RDRAND.

... and most of these systems have TPM chips with a RNG, which is (alas)
usually only used at system startup, as that hw_rng device sets its quality
to 0 (meaning untrusted). So there's also room for improvement involving
these hw rng devices.

Thanks,
	Dominik