From: dwp@sunsrvr3.cci.com (Dana Paxson)
Newsgroups: comp.society.privacy
Subject: Encrypted Communications
Date: 29 Jul 92 16:20:06 GMT
Organization: Computer Privacy Digest
X-Submissions-To: comp-privacy@pica.army.mil
X-Administrivia-To: comp-privacy-request@pica.army.mil
X-Computer-Privacy-Digest: Volume 1, Issue 068, Message 2 of 7


** LONG **

In general, I think laws making encrypted communications illegal 
are wasteful, stupid and oppressive, for the following reasons:

1)	They would be a violation of free speech rights.

2)	They would be a waste of time and effort, since 
	determining violation can be impossible.

3)	They would be a further waste of time and effort, 
	since such laws are impossible to enforce.

4)	They would allow a government to apply enforcement
	selectively, singling out a few (for arbitrary
	reasons) and prosecuting them under the vague
	suspicion that some communication contained en-
	crypted matter.

Point 1) seems self-evident to me.

Regarding Points 2) - 4):

A few examples and demonstrations come to mind.  One of the
most interesting and illuminating is the old 'Bacon cipher' 
controversy:  the notion that Shakespeare's folios contained 
subtle typeface variations that amounted to an encipherment 
of text written by Francis Bacon, text which indicated that 
Bacon was actually the author of the Shakespeare plays.

As I remember it, there was a heated scholarly controversy 
over this idea for many years, which had all the earmarks of 
crankdom making an assault on basic literary understanding.  
Both sides of the debate attracted large numbers of followers.  
It was all put to rest (at least from a scientific point of 
view) when one researcher who understood cryptography quite 
well managed to demonstrate that by reading the supposed 
typeface variations in different ways and supplying some 
additional overlays or adjustments of data (which the pro-
Bacon people said was necessary to read the hidden text), he 
could make Shakespeare's folio produce any hidden text he 
wanted it to!

Admittedly the cryptographic methods assumed by the pro-Bacon
group were faulty, and modern cryptanalysts would not make
the mistake of inserting a text-decryption overlay that in 
effect would be inserting the encrypted message they wanted 
to find.  Any astute analyst would spot this immediately. 
The trouble is that not everyone involved in trying to make
determinations of violation of anti-encryption law is quali-
fied either to avoid making such an analytical error or to
catch one being made.  And this statement makes no assump-
tion of malice.  What if malice IS the motive?

So perhaps someone might count the characters in each line in
this posting, convert the counts to characters with some 
simple arithmetic function, apply some transformation (either
transposition or substitution, with some arbitrary key) and
decide that I am a dangerous subversive because of the resul-
ting "content" emerging from this process.  There is in fact
no such content.

Another such someone might profess to have found another
message of mine which, when used as a key, produces a plain-
text from selected words in this message.  Between selecting
another message, and selecting the words, they could put
any concealed text in my message that they wanted to find.

Behind all this is the greasy odor of pseudoscience.  Once
a pseudoscientist sets mind on getting a result, all evidence
leads to it.  Or, as one wag put it, "When the theory does not
agree with the facts, the facts must be disposed of."  Mix
the pseudoscientists with the oppressive or manipulative 
politicians, and the results can be explosive.

It is a dangerous farce.  It could be worse law.

Turning to the other end of things, can any REAL concealed
ciphertext be detected?  The answer is, simply, no.  The
reason, strangely enough, is virtually the same as the reason
that the Bacon-cipher people thought they had succeeded.  
All the correspondents need to do is to establish two entirely
independent communications pathways, sending the apparent
plaintext message over one channel, and a key for extracting 
other messages from it over the other.  Unless a cryptanalyst
has access to both channels, no encrypted message sent on one 
channel can be decrypted if the encryption was done with a 
key based on a one-time pad (a once-used series of characters 
or values) sent over the other channel.  The Bacon-cipher
people did this unwittingly when they created the data 
overlays, which amounted to the key.

The channels need not occupy the same medium, nor the same
place or time.  A private conversation can serve as one
channel, and the public network(s) the other.  So if I wanted
to plant an encrypted message in this message, I would only
have to set up a key to produce it, and send the key via let-
ter, radio, telephone, carrier pigeon, whisper, etc. to the
intended recipients of the hidden message.  If I took care
with that communication, no one would have a clue.

And I could make this message contain two entirely contra-
dictory encryptions for two different recipients, just by
sending them different keys.

As an aside, this is how some people who tell fortunes or 
interpret holy scriptures make a living.  I'm not referring 
to honest students of scripture or human nature, only to the 
folks with an axe to grind or money to be made.  Such people 
can be extremely dismissive of scientific argument and 
evidence.


Hoping my recollections of the Bacon cipher controversy are 
basically accurate,

Dana Paxson
Network Applications Systems Group
Northern Telecom
97 Humboldt Street
Rochester, New York  14609

dwp@cci.com

1 716 654-2588

Disclaimer:  The opinions expressed above are mine personally,
	     and do not necessarily reflect the views of my 
	     employer.