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Introduction- Telephone

   When you have an untappable wire
   between the sender and recipient, then traffic analysis is impossible (and
   crypto unnecessary).

Yet you can create an untappable wire with cryptography!  The device
in question is called a link encryptor.  Take a stream cipher and run
it continuously across the channel in question.  Pad the asynchronous
traffic when it's not flowing and add some synchronization to both the
stream and the data insertion.

You can tap the physical line still, but the interceptions reveal zero
information (computationally--the stream cipher _is_ keyed, after

A good project would be virtual link encryptors for the Internet.