Fractal cryptography

[hfinney@shell.portal.com (Hal Finney)]

There have been some discussions on sci.crypt within the past few months
on nonlinear/chaotic algorithms and their use in cryptography.  Fractal
cryptography sounds like it might be related.  The problem is that unless
an algorithm was SPECIFICALLY DESIGNED to prevent an intelligent adversary
from defeating it, the chances of it being an effective cryptosystem are
limited.  Just because nonlinear systems produce complex-looking results
does not mean that these results are unpredictable given enough data.

Now, maybe this particular fractal cryptosystem idea will actually work
well.  I don't know; I haven't seen it.  But the point is that these
complex types of systems have not provided a good foundation for crypto-
graphy in the past.

sci.crypt messages are available on (at least) ripem.msu.edu, in
/pub/crypt/sci.crypt.  In that directory there is a file "subjects",
which lists all the subject lines by message number, as well as a collection
of files each of which holds a couple of months' worth of messages.  You
can grep the subjects file to find those messages which might be i{terested.
The archives appear to go back a couple of years.

Hal