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Re: /dev/random is probably not
From: Stefan Bethke <s.bethke () tallence com>
Date: Fri, 8 Jul 2005 22:27:25 +0200

Am 07.07.2005 um 02:53 schrieb Kai Howells:

[ Mac OS X entropy pool being periodically saved to a file and used on boot to prime the PRNG ]

Now this raises some interesting issues - such as where is the entropy written to, and how much does this pool of entropy set the state of the RNG after bootup - ie, if an attacker had control of this file, could they influence the RNG in a deterministic fashion after forcing a reboot?

$ ls -l /private/var/db/SystemEntropyCache
-rw------- 1 root wheel 20 Jul 8 21:59 /private/var/db/ SystemEntropyCache

If an attacker can manipulate this file, he probably has much more effective tools to control the system...

FreeBSD 5 uses a similiar mechanism:
http://www.freebsd.org/cgi/man.cgi? query=random&apropos=0&sektion=4&manpath=FreeBSD+5.4-stable&format=html

$ sudo ls -la /var/db/entropy
total 20
drwx------  2 operator  operator   512 Jul  8 22:22 .
drwxr-xr-x  8 root      wheel      512 Jul  8 22:21 ..
-r--------  1 operator  operator  2048 Jul  8 22:22 saved-entropy.1
-r--------  1 operator  operator  2048 Jul  8 22:11 saved-entropy.2
-r--------  1 operator  operator  2048 Jul  8 22:00 saved-entropy.3
-r--------  1 operator  operator  2048 Jul  8 21:55 saved-entropy.4
-r--------  1 operator  operator  2048 Jul  8 21:44 saved-entropy.5
-r--------  1 operator  operator  2048 Jul  8 21:33 saved-entropy.6
-r--------  1 operator  operator  2048 Jul  8 21:22 saved-entropy.7
-r--------  1 operator  operator  2048 Jul  8 21:11 saved-entropy.8


--
Stefan Bethke <s.bethke () tallence com>
Tallence GmbH, Baumwall 3, D-20459 Hamburg, Germany
Mobile +49 170 3460140, Office +49 40 360935-0, Fax +49 40 360935-10



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