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Date:   Thu, 9 Jan 2020 14:30:48 -1000
From:   Andy Lutomirski <luto@...capital.net>
To:     Kurt Roeckx <kurt@...ckx.be>
Cc:     "Theodore Y. Ts'o" <tytso@....edu>,
        Stephan Mueller <smueller@...onox.de>,
        Andy Lutomirski <luto@...nel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Linux API <linux-api@...r.kernel.org>,
        Kees Cook <keescook@...omium.org>,
        "Jason A. Donenfeld" <Jason@...c4.com>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        "Eric W. Biederman" <ebiederm@...ssion.com>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        Michael Kerrisk <mtk.manpages@...il.com>,
        Willy Tarreau <w@....eu>,
        Matthew Garrett <mjg59@...f.ucam.org>,
        Ext4 Developers List <linux-ext4@...r.kernel.org>,
        linux-man <linux-man@...r.kernel.org>
Subject: Re: [PATCH v3 0/8] Rework random blocking



> On Jan 9, 2020, at 12:02 PM, Kurt Roeckx <kurt@...ckx.be> wrote:
> 

> 
> If the kernel provides a good RNG, the only reason I can see why
> you would like to have direct access to a hwrng is to verify that
> it's working correctly. That might mean that you put it in some
> special mode where it returns raw unprocessed values. If the device
> is in such a mode, it's output will not provide the same entropy
> per bit, and so I would expect the kernel to stop using it directly.

I disagree.

If I buy a ChaosKey or a fancy EAL4FIPSOMG key, I presumably have it for a reason and I want to actually use the thing for real. Maybe it’s for some certification reason and maybe it’s just because it’s really cool.

As for “direct” access,  I think AMD provides an interface to read raw output from the on-die entropy source. Exposing this to user space is potentially quite useful for anyone who wants to try to characterize it.  I don’t really think people should use a raw sample interface as a source of production random numbers, though.

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