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Date:   Fri, 13 May 2022 08:19:13 +0200
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?
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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