From: koontzd@lrcs.loral.com (David Koontz )
Date: Wed, 26 Jan 94 11:27:10 PST
To: tcmay@netcom.com
Subject: Re: clipper pin-compatible chip
Message-ID: <9401261919.AA22973@io.lrcs.loral.com>
MIME-Version: 1.0
Content-Type: text/plain


>From: m5@vail.tivoli.com (Mike McNally)

>I don't think the idea proposed is to reverse-engineer the Clipper.
>Rather, the idea is that once you know the pin-out you can make an
>electrically-compatible (and, in important ways, software-compatible)
>replacement.

While the clipper chip and its CCEP brethern have chip specifications 
that imply that key is supplied as long as a read flag is in a certain
state.  The key for the clipper chip is 10 bytes of actual key plus
3 bytes of cryptographic check word (CCW), for a total of 13 bytes.

Operating in a system expecting a clipper chip potentially restricts
the keyspace.  Non-centrally selected keys use the clipper chip to
'fish' for the CCW, where it is re-fed.  The host system (to the 
clipper chip) is going to try and feed 10 bytes plush 3 bytes of
a constant.  Utilizing IDEA, the key is supposed to be 16 Bytes.

The point being that dropping an IDEA chip in is not 'plug and play'.