From: nelson_p@apollo.hp.com (Peter Nelson)
Subject: Re: [comp.org.eff.talk] Latest FBI Wiretap Bill
Date: Thu, 3 Sep 1992 17:20:26 GMT
Organization: Hewlett-Packard Corporation, Chelmsford, MA

In article <1992Sep3.155535.471@tvnews.tv.tek.com> stever@crosstalk.tv.tek.com (Steven E. Rice  P.E.) writes:
>In article <Btyz8z.K3K@apollo.hp.com>, Peter Nelson (nelson_p@apollo.hp.com)
>asked how it was possible for the government to tell if communciations had
>been encrypted.  He added:
>
>>                                                           . . .  I've
>> been experimenting for some time with "clear text" encryption methods
>> in which the content appears to be perfectly normal email and postings, 
>> but which include additional data.   Since the data is represented as
>> the statistical variance in the use of synonyms and by other similar
>> means these are virtually undetectable, and encrypted messages can
>> easily be piggybacked onto perfectly legitimate messages.
>
>Don't be fooled!  THESE PEOPLE AREN'T AMATEURS!!!  Methods such as
>you describe were used by spies in World War II, and the "secret"
>messages were routinely intercepted and decoded.  Cryptology has
>advanced significantly since then.

  The methods used in WWII were very simple compared to mine. And even
  then the clear-text methods often required outside sources of
  information or other tricks to break.  An example of such a method
  from WWII that was successfully broken was the means the Americans
  used to identify that Midway was the target of an intended Japanese
  attack.  They (the Americans) had to broadcast an unencrypted message
  pertaining to a broken water desalinization unit on Midway and wait
  to see references to this in the Japanese transmissions.  In other
  words it required more than the text itself to break.  

  The whole point of clear text encoding (or any encryption method)
  is that not all the information is contained in the message.  The
  feds might discern with their computers that the ratio of, say, 
  the letter "s" to the letter "p" varies in a certain way, but 
  the *meaning* of this is only known to the sender and intended
  receiver.  And the other thing is that when you look at all the
  possible things you can vary in an ASCII message of several hundred
  or thousand characters, even the fastest computer on earth running 
  for centuries cannot examine all possible permutations of these
  things.  


>There are foolproof encodings for data, but the statistics of the
>messages will clearly reveal that they are encoded.  The very next thing
>you'll hear is the KNOCK, KNOCK, KNOCK of the FBI on your  door.  You
>will then have a chance to explain just why you are encoding your
>communications.  The judge may not be very sympathetic.

  First they have to show that it IS encoded.  Which in the case of
  clear-text is very hard to do, because when you perform the statistical
  analysis you describe on even UNencrypted text you'll find all kinds 
  of patterns and statistical "features" simply because each writer
  has his unique writing style.   I'm currently building up a database
  of postings from Compuserve posters at home and am enjoying some
  early successes in using the computer to identify who the poster
  is by statistically anaylzing blocks of their text.  


---peter




Xref: sparky alt.society.civil-liberty:5649 alt.privacy:1792