🚀 go-pugleaf

In article <1992Nov20.162319.24428@rchland.ibm.com> I wrote:

>Consider the press release.  It is sent, in encrypted and padded form
>to 100 branch offices of Fortune 500 firm X.  The opponent intercepts
>some of these.

>A day later, the plain text is published verbatim, freely available.
>The opponent counts the bytes and goes "aha".
>
>This sort of thing is not uncommon and would reveal the padding pretty
>readily; deciding which text was the press release is a separate problem,

   ". . .deciding which text was the press release"

  That is to say, which of the many intercepted encrypted messages that
  day was the press release as opposed to some other encrypted message
  sent that day.

>but 100 copies of the same thing is a pretty good clue. . .and this
>exact kind of attack _has_ succeeded many times.  Government crypto
>groups spend a lot of time on it.  They can often correlate very 
>accurately even when the can't solve the cipher.

   "correlate very accurately even when they can't solve. . ."

   That is to say, they can often be very sure about which message is
   the press release even when they can't solve it.  This analysis is
   called "traffic analysis".  As far as I know, there is no way to
   prevent the traffic analysis part in general, though maybe it can
   be beaten off with enough super-encryption.  The basic problem is that
   one can figure out that some message was sent from Washington to Berlin,
   and thereby begin to sort out what messages went with what later public
   text.  Repeated messages (say, a simultaneous press release in
   the same language, released from multiple sites) are especially tough
   to guard against.

   In any case, it is a separate problem, needing to be solved separately,
   and most people don't even know it is a problem.

-- 
   Larry W. Loen        |  My Opinions are decidedly my own, so please
                        |  do not attribute them to my employer