From: mikepb@freke.lerctr.org (Michael P. Brininstool)
Date: Thu, 22 Dec 94 02:39:58 PST
To: cypherpunks@toad.com
Subject: Hash functions & Physical Analogies
Message-ID: <1994Dec22.103705.26972@freke.lerctr.org>
MIME-Version: 1.0
Content-Type: text/plain


I seem to remember someone mentioning that a hash function, like the
one used in signatures in PGP, would show a large change for a small
change in the file, and a small change for a large change in the file.

I was digging through some of my old stuff last weekend with my kids
and found my old Rubik's Cube.  I set it aside until last night.

Here is the connection.  It was late, but I decided to try and figure
out some "move" sequences that would move small numbers of blocks on
the Rubik's cude, without changing the location or orientation of the
rest.  In doing this, I (re)noticed that simple "move" sequences resulted
in a large number of displacements (translation and/or rotation) of the
blocks in the cube.  And that very large sequences of "moves" had the
opposite effect (if it was the correct sequence).

This, in my sleep deprived state, brought hash functions to mind.  It
also brought several questions to mind.

First question:
	I think I have seen references to topology in discussions of
	cryptography.  I have never had a topography class, so I was
	wondering, is Rubik's cube is a topology problem?

Second question:
	If Rubik's cube is a topo prob, is it a good analogy for trying
	to describe hash functions to people?

Third question:
	If there is an analogy, how do you convince the lay person that the
	hash is a one-way function?  By demonstrating that it maps many to
	one, and the Rubik's Cude maps one to one?

Fourth question:
	To sign a post with PGP (from within vi, under trn)  Do I include
	the header in the lines to be run through 'pgp -fast' or not?
	(I have the cp list go into a news gateway on my home machine so
	that threads are easier to follow)

---------------------------------------------------------------|
| #include "std/disclaimer.h"           Michael P. Brininstool |
| mikepb@freke.lerctr.org         OR         mikepb@netcom.com |
| (408)251-3222(Home) (415)253-0853(Pager) (415)694-1882(Work) |
|---------------------------------------------------------------