linux-kernel - Re: Linux 5.3-rc8

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Message-ID: <20190917171641.GC27999@1wt.eu>
Date:   Tue, 17 Sep 2019 19:16:41 +0200
From:   Willy Tarreau <w@....eu>
To:     Matthew Garrett <mjg59@...f.ucam.org>
Cc:     Linus Torvalds <torvalds@...ux-foundation.org>,
        Martin Steigerwald <martin@...htvoll.de>,
        "Ahmed S. Darwish" <darwish.07@...il.com>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Vito Caputo <vcaputo@...garu.com>,
        Lennart Poettering <mzxreary@...inter.de>,
        Andreas Dilger <adilger.kernel@...ger.ca>,
        Jan Kara <jack@...e.cz>, Ray Strode <rstrode@...hat.com>,
        William Jon McCann <mccann@....edu>,
        "Alexander E. Patrakov" <patrakov@...il.com>,
        zhangjs <zachary@...shancloud.com>, linux-ext4@...r.kernel.org,
        lkml <linux-kernel@...r.kernel.org>
Subject: Re: Linux 5.3-rc8

On Tue, Sep 17, 2019 at 05:34:56PM +0100, Matthew Garrett wrote:
> On Tue, Sep 17, 2019 at 09:27:44AM -0700, Linus Torvalds wrote:
> 
> > Does anybody believe that 128 bits of randomness is a good basis for a
> > long-term secure key?
> 
> Yes, it's exactly what you'd expect for an AES 128 key, which is still 
> considered to be secure.

AES keys are for symmetrical encryption and thus as such are short-lived.
We're back to what Linus was saying about the fact that our urandom is
already very good for such use cases, it should just not be used to
produce long-lived keys (i.e. asymmetrical).

However I'm worried regarding this precise patch about the fact that
delays will add up. I think that once we've failed to wait for a first
process, we've broken any hypothetical trust in terms of random quality
so there's no point continuing to wait for future requests.

Willy