[5233] in cryptography@c2.net mail archive
Re: depleting the random number generator
daemon@ATHENA.MIT.EDU (Bill Frantz)
Tue Jul 27 10:32:04 1999
In-Reply-To: <Pine.LNX.4.04.9907261020360.30088-100000@ultra.gawth.com>
Date: Mon, 26 Jul 1999 21:42:37 -0700
To: bram <bram@gawth.com>, John Kelsey <kelsey.j@ix.netcom.com>
From: Bill Frantz <frantz@netcom.com>
Cc: cryptography <cryptography@c2.net>
At 10:35 AM -0700 7/26/99, bram wrote:
>A lot of things include less entropy than one might assume. For example,
>keystrokes contain essentially no entropy based on what letter was hit,
>and the number of bits of entropy their timing includes is approximately
>the logarithm of the number of time ticks since the last keystroke. (which
>means, interestingly enough, that you can get faster entropy harvesting by
>having a more precise clock.)
However, the simple technique of using the CPU's cycle counter as a clock
may not give you the more precise clock you are looking for. If the
keyboard uses a microprocessor to scan the keys and report the scan codes
as interrupts, then its clock is likely to be the one controlling the
precision.
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