From: wcs@anchor.ho.att.com (bill.stewart@pleasantonca.ncr.com +1-510-484-6204)
Date: Tue, 15 Feb 94 19:24:36 PST
To: cypherpunks@toad.com
Subject: Re: LEAF, SS7
Message-ID: <9402160309.AA08927@anchor.ho.att.com>
MIME-Version: 1.0
Content-Type: text/plain


With the mail flood here, I've seen pieces of the answer, but no summary.
While Clipper and SS7 both give the Wiretappers part of the traffic analysis,
Clipper would be much more effective (if it were widely used by Wiretappees.)
SS7 is hard to tap, unless you have the phone company's cooperation,
somewhat hard even with it, and Async Transfer Mode will be harder.
Also, SS7 can only tell you what phone line is being used; Clipper tells
you what *phone* is being used, and one of the major wiretap targets
for Clipper are cellular phones, which people normally carry around with them -
so Clipper traffic analysis can tell you *who* is talking, once a phone's
serial number has been identified, not just what pay phone the conversation
is from.

The two can be used together, if the Wiretappers are both lucky and persistent.
One presumes that if ClipperCellPhones are widely used, they'll start keeping
records of which cellphone numbers correspond to which ClipperIDs,
by wiretapping (or radiotapping) and listening for Clipper.
For instance, if they're tapping SS7, and see a phone call from a well known
activist's phone number to a recognizeable cellphone company, 
they can correlate the phone number to find the ClipperID,
which makes tapping easier and puts that cellphone on the fun-to-watch list.

		Paranoidly :-),   Bill