From: Michael Paul Johnson <mpj@ebible.org>
Date: Wed, 5 Aug 1998 21:03:10 -0700 (PDT)
To: cypherpunks@toad.com
Subject: Re: Noise source processing
In-Reply-To: <Pine.LNX.3.96.980805210406.11770A-100000@albert>
Message-ID: <199808060403.XAA32439@yeti.host4u.net>
MIME-Version: 1.0
Content-Type: text/plain


At 09:12 PM 8/5/98 -0400, mgraffam@mhv.net wrote:
...
>After a little bit of work I have put together a white noise source 
>(hacked FM reciever, heavily shielded to reduce local EMR bias) and
>have it jacked into a mic port on one of my machines. I would like
>to develop of bit of code (oh, horror :) to take bits from the sound
>card, and bits from /dev/random, and mix them together to get a
>random number stream.
>
>The noise coming off of the sound card is more beige than white though..
>
>Does anyone know of any papers, articles or whatever on good techniques to
>remove bias from the audio source? 
...
If I were doing it, I would probably feed the raw bytes into a stream
cipher with feedback, like Sapphire II, and then select every nth byte from
the output stream (just to match the output bit rate to the estimated
actual entropy in a conservative fashion and improve the effective
avalanche performance of that particular algorithm). This would be faster
than a hash like SHA-1. Indeed, you could just use a good mixer, like a CRC
or non-cryptographic hash to whiten the noise if speed is an issue. As long
as you restrict the output bit rate to less than the actual estimated
entropy of the source, you should be alright, provided that your noise
source is as random as you think it is.

Then again, the truly paranoid may beg to differ.




_______

Michael Paul Johnson                   
mpj@ebible.org    http://ebible.org    http://cryptography.org
PO BOX 1151, Longmont CO 80502-1151, USA Jesus Christ is Lord!