From: nikb@cix.compulink.co.uk (Nick Barron)
Newsgroups: sci.crypt
Subject: Bitz & Bobz
Date: 12 Oct 92 22:37:43 GMT
Reply-To: nikb@cix.compulink.co.uk

Hi!

Please excuse several responses lumped into one, but my Usenet access is
currently via e-mail!!

In <81390@ut-emx.uucp>, Douglas Floyd writes:

>For a REALLY secure computer, just low-level format the HD after use.

Try telling that to GCHQ/NSA!  Governement regs involve repeated writes
of 0s then 1s (three times) followed by a single-byte written and verified.
This is because some people (including Dr.Solomon!) have equipment that can
rescue data from re-formatted discs!  I personally favour the 150g-of-C4
secure erasure method! (i suppose that would be known as "diffusion"!)

In <1bar0dINNck1@usenet.INS.CWRU.Edu>, David Lesher made some comments...

Sorry, I may have been misunderstood....  what I meant was, the *official*
history says it wasn't cracked, but most of the details are *still* highly
classified and likely to remain so.  My point is, if it *was* cracked, GCHQ
would probably not publicise the fact (these people don't even identify 
themselves when you phone...they just say 'Hello..'!).  Some sources
(Secret Intelligence, Volkman & Baggett) state that Enigma machines (although
I admit, not the naval ones) were sold off to "small nations", with the
spooks neglecting to let them know they may as well publish their secrets in
a newspaper!!

And as for keeping secrets, I sympathise.... it's *embarassing* when the MD
introduces a customer to you and asks you what you're doing and you have to
say "sorry, I am not permitted...."

Quantum Cryptography:

I am in agreement with Joe Thomas on this (on a purely amateur basis -
quantum physics is a "hobby" if thats the right term!).  As far as the Bell's
Theorem bit goes, the following extract from "In Search of Schroedingers Cat"
by John Cribbin may explain things:

" This does not mean that there is any likelihood of being able to send
  messages faster than the speed of light.  There is no prospect of 
  conveying useful information in this way, because there is no way of
  linking one event that *causes* another event to the event it causes
  through this process.  It is an essential feature of the effect that it
  only applies to events that have a *common* cause -- the annihilation of
  a positron/electron pair; the return of an electron to the ground state;
  the separation of a pair of protons from the singlet state.  You may
  imagine two detectors situated far away in space, with photons from some
  central source flying off to each of them, and you may imagine some
  subtle technique for changing the polarization of one beam of photons,
  so that an observer far away sees changes in the polarization of the other
  beam.  But what sort of signal is it that is being changed?  The original
  polarizations, or spins, of the particles in the beam are a result of
  random quantum processes, and carry no information in themselves.  All that
  the observer will be seeing is a different random pattern from the random
  pattern that he would see without the cunning manipulations of the first
  polarizer!  Since there is no information in a random pattern, it would
  be totally useless.  The information is contained in the difference
  between the two random patterns, but the first pattern never existed in
  the real world, and there is no way to extract the information"

  Thanks, John!  (and it's a great book, by the way).

Well, thats all for now!

NikB

    "Why didn't Schroedinger get in the bloody box?" - My cat, Rusty.