Date: Thu, 26 Oct 2000 13:29:33 -0700 From: Mark Murray <mark@grondar.za> To: Doug Barton <DougB@gorean.org> Cc: current@FreeBSD.org Subject: Re: entropy reseeding is totally broken Message-ID: <200010262029.e9QKTXM00442@grimreaper.grondar.za> In-Reply-To: <Pine.BSF.4.21.0010261218110.15371-100000@dt051n37.san.rr.com> ; from Doug Barton <DougB@gorean.org> "Thu, 26 Oct 2000 12:49:47 PDT." References: <Pine.BSF.4.21.0010261218110.15371-100000@dt051n37.san.rr.com>
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> I stated this same objection until I actually attended Mark's
> presentation at the 'con. The yarrow algorithm uses an encrypted hash for
> the entropy on the way in, and encrypts the output on the way out. This
> would make it extremely difficult to guess the state at reboot, even if we
> weren't picking up new entropy sources during the boot process.
There is an angle; an attacker can attack by replaying, but this requires
strong privelige.
> Pending Mark's approval, I'd like to suggest we add a cron job to
> dump X k of data from /dev/random to a file (/boot/.periodic_entropy
> maybe?) and use that, AND ${entropy_file:/var/db/entropy} to reseed at
> boot, and only do the "long, annoying" failover process if neither file
> exists. The only remaining questions would be how many k of data to dump
> how often.
I like that, but I'd like to see more than one file. This avoids the race
where fsck may blat an incompletely written file after a (in)convenient
crash.
We are really headed towards saving state in the first swap partition
(if there is one).
On a related note, I'd like to see mergemaster rebuild /dev if it is not
DEVFS (obviously taking into account user preferences in MAKEDEV.local).
I believe that users are shootin their feet by not tracking /dev properly.
M
--
Mark Murray
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