🚀 go-pugleaf

In article <1992Jul31.153719.28374@ncsu.edu> Webbge@che17.ncsu.EDU
(Greg Earl Webb) writes:
>I've seen some interesting posts here recently, but I have yet to
>see the topic of padding data with garbage.  It seems to me that
>if you had an algorithm that would not only encrypt the data, but would
>also insert random data into the original data (without following
>a regular pattern) that it would be almost impossible for someone
>to tell what was real information and what was just junk.  Although
>the size of the document would increase, the difficulty in decrypting
>the message would also increase considerably.
>
>The only problem I can see with this method is how do you insert data
>in a non-regular pattern and still have the ability to remove it later.
>Please comment on this type of procedure.

Clearly it's important that you *do* have the ability to remove it
unambiguously later.  Kahn "The Codebreakers" p.608-609 contains a
story from World War II describing the problems that once ensued
when improper padding *wasn't* removed (i.e. was taken as message
text) in a US Navy message during the battle of Leyte Gulf in 1944:

	Naval communication procedure called for the head
	and the tail of messages -- their most vulnerable
	points -- to be concealed by nulls consisting of
	meaningless words.  This ``padding'' was supposed
	to be totally alien to the text, but the enciphering
	ensign in Pearl Harbour violated this rule when he
	used a phrase that was ``just something that popped
	into my head.''  Though he correctly set the padding
	off from the text by doubled letters, communicators
	on [US Navy Admiral] Halsey's flagship decided against
	removing it on the chance that it might be part of
	the message.  Thus, the decipher tape that they rushed
	to Halsey read:

		From CINCPAC [Nimitz] action Com Third
		Fleet [Halsey] info Cominch [King] CTF
		seventy four [Kinkaid] X Where is repeat
		where is Task Force thirty four RR the
		world wonders

The final three words (the padding) were taken as a personal
insult, with various ensuing mixups resulting.

- Jonathan Thornburg
  <jonathan@einstein.ph.utexas.edu> or <jonathan@hermes.chpc.utexas.edu>
  University of Texas at Austin / Physics Dept / Center for Relativity
  and (for a few more months) U of British Columbia / {Astronomy,Physics}