AT&T Encrypting Phone Ad in WS Journal

[binski at u.washington.edu]

FYI

The Wall Street Journal, 7 June 93, page B7, has an AT&T ad for an
encrypting communications box called "Surity Telephone Device".
It plugs between a regular phone and the phone jack.
Anybody know what's inside?  Is this new?  

Also, page B6 has a so-so article on digital signatures.

bf