linux-kernel - Re: urandom is too slow

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Message-ID: <20121030185403.GA5044@thunk.org>
Date:	Tue, 30 Oct 2012 14:54:03 -0400
From:	Theodore Ts'o <tytso@....edu>
To:	Lasse Kärkkäinen <ljkarkk2@...hut.fi>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: urandom is too slow

On Tue, Oct 30, 2012 at 04:55:22PM +0200, Lasse Kärkkäinen wrote:
> Apparently there has been little or no development on urandom even
> though the device is in widespread use for disk shredding and such
> use. The device emits data at rather slow rate of 19 MB/s even on
> modern hardware where other software-based PRNGs could do far
> better. An even better option seems to be utilizing AES for
> encrypting zeroes, using a random key, allowing for rates up to 500
> MB/s with hardware that has AES-NI instructions.
> 
> Why is urandom so slow and why isn't AES hardware acceleration utilized?

If you can use a software-based PRNG, you should use one in userspace.
The intended use of urandom is for cryptographic purposes (i.e.,
generating random session keys, long-term public keys, etc.).  If you
just want to wipe a disk, you shouldn't be using /dev/urandom for that
purpose.

Regards,

						- Ted
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