Re: [PATCH] (0/4) Entropy accounting fixes

[Pavel Machek <pavel@suse.cz>]

Hi!

> >  What entropy can be measured from disk timings are very often leaked
> >  by immediately relaying data to web, shell, or X clients.  Further,
> >  patterns of drive head movement can be remotely controlled by clients
> >  talking to file and web servers. Thus, while disk timing might be an
> >  attractive source of entropy, it can't be used in a typical server
> >  environment without great caution.
> 
> This is something to be concerned about, to be sure.  But generally a
> client won't have complete control of the drive head movement ---
> there are other clients involved --- and the adversary generally won't
> have complete knowledge of the block allocation of files, for example,
> so he/she would not be able to characterize the disk drive timings to
> the degree of accuracy required.

You seem  assume that adversary is on remote system. That's not neccessarily
the case.

Imagine you wanting to generate gpg key while I have normal user account
on the machine. I can sample /proc/interrupts, measure disk speeds etc...
Perhaps we are alone on [otherwise idle] machine. You still don't want me 
to guess your key.

								Pavel
-- 
Philips Velo 1: 1"x4"x8", 300gram, 60, 12MB, 40bogomips, linux, mutt,
details at http://atrey.karlin.mff.cuni.cz/~pavel/velo/index.html.