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Sources of randomness

>Date: Thu, 2 Nov 1995 00:39:29 -0800
>From: [email protected] (Timothy C. May)

>Digitized video input, especially from something like a noisy channel (t.v.
>channel, for example), is quite likely to produce a lot more entropy bits
>per second than nearly any of us ever need. (One's PGP key could be seeded
>in a fraction of a millisecond, for example.)

My cable feed into my Mac, for example, has surprisingly little noise --
and it's only local noise (stuff only at my house, not available to the
eavesdropper) which counts as entropy.

>  One of the basic ideas we
>have had, as Cypherpunks, is to encourage widespread methods. Any methods
>that need special hardware tend to not get widely used.
>Audio, video, disk timing, and all sorts of other sources of physical
>randomness are useful to have, but most people either won't have the right
>configuration or won't configure their systems so as to use their

Most Macs and PCs have audio inputs.  Most of those are mono,
unfortunately.  [The numeric difference between two stereo mics is
especially hard for an eavesdropper-wannabe to predict/compute, assuming
the room isn't silent.]  However, if the eavesdropper doesn't have a mic in
your room, there's still some entropy available on the mono channel.

Meanwhile, my old Sparcstation 1 had an A-D which, when no mic was
connected, gave about 1 bit/second of entropy.  (The newer Sparc here gives
solid 0's with no mic.)

Recorded audio is useless as entropy, of course.

Almost all computers have a mouse and a normal signature, hand-written with
a mouse, has great gobs of noise.  (I'm still working on the little PC
program to measure this -- but preliminary results show a minimum of 1 bit
of noise per mouse sample -- or 200 bits per signature.  Final results may
get higher entropy rates, but I'll wait for the real results before
claiming that.)

|Carl M. Ellison      [email protected]    http://www.clark.net/pub/cme	   |
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