On Wed, Apr 24, 2013 at 03:37:37AM +0200, Vincent Lefevre wrote:
> On 2013-04-23 20:06:10 -0500, Derek Martin wrote:
> > Using the message store or any part of the message store is not a
> > workable solution.  
> 
> I disagree. 

The security experts all agree on this... if you try to implement
something like that, it will not withstand a rigorous security audit.

> The entropy is typically created from untrusted data.

Only indirectly, in a way that an attacker can not control without
direct access to the target's hardware.  On anything resembling a
modern system, entropy is generally generated by measuring hardware
timings (disk access, key presses, etc.), reading electrical noise
from sound hardware, and other similar things that an attacker has no
control over--unless they have physical access to the hardware, in
which case you already pretty much lose.
 
> Note that message headers generally contain random data from different
> machines; 

It's NOT random.  It's very predictable, if you're familiar with the
receiver's site.  And if you (the attacker) are AT the receiver's site
(i.e. you're another user on the public server they're using to get
their mail), all you need to do to get an EXACT COPY of the message is
to CC yourself.

You MUST NOT use the message as a source of randomness.

-- 
Derek D. Martin    http://www.pizzashack.org/   GPG Key ID: 0xDFBEAD02
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