linux-kernel - Re: drivers/char/random.c: variable type mismatch

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Date:	Thu, 8 Nov 2012 06:47:08 -0500
From:	Theodore Ts'o <tytso@....edu>
To:	Stephan Mueller <stephan.mueller@...ec.com>
Cc:	lkml <linux-kernel@...r.kernel.org>
Subject: Re: drivers/char/random.c: variable type mismatch

On Thu, Nov 08, 2012 at 01:32:38AM +0100, Stephan Mueller wrote:
> 
> However, due to the fact that jiffies provides very few entropy, the
> event value provides (almost) none, the majority of entropy comes from
> the processor cycles. Assuming that the processor cycles increase once
> per nanosecond, after 2**32 cycles (about 4 seconds), the counter wraps.

Sure, we can make this change, but it doesn't make as much difference
as you think.  The high 32 bits gets incremented about ounce every 4
seconds, while jiffies gets incremented once every 1/HZ seconds.  But
the point is they are pretty well correlated (i.e., if you know the
jiffies values A' and A'', and I know the high 32 bits of the cycles
B', and you can determine the likely value of B'' to a very high
degree of accuracy.  Values which are correlated don't actually
entropy.

							- Ted
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/