From: szabo@techbook.com (Nick Szabo)
Date: Tue, 20 Apr 93 21:08:38 PDT
To: cypherpunks@toad.com
Subject: European front: wiretapping vs. GSM
Message-ID: <m0nlW9s-000hv7C@techbook.techbook.com>
MIME-Version: 1.0
Content-Type: text/plain



Forwarded from comp.dcom.telecom:

Subject: Re: Truly Amazing, Truly Amazing ... Feds
Reply-To: Michael_Lyman@sat.mot.com
Message-ID: <telecom13.254.17@eecs.nwu.edu>
Organization: Motorola Inc. - Satellite Communications
Sender: Telecom@eecs.nwu.edu

In article 1@eecs.nwu.edu, naddy@mips.ruessel.sub.org (Christian
Weisgerber) writes:

> I wonder, is the signal only digitally encoded or digitally encoded
> and *additionally* encrypted?

Yes on both counts. On the air interface between the base station (
BSS ) and mobile station ( MS ) the signals are digitally encoded.
Traffic channel rate is 13 Kb/s. In addition to this, ciphering is
done to protect the signalling channel such that user data privacy is
provided then, encryption is provided for all voice traffic. As an
aside, the GSM system also assigns "alias" subscriber numbers which
are changed automatically with ( usually ) every call -- the
subscribers real phone number is never ( well, almost never ) used
over the air.

> I'm getting a little paranoid over this, but in Germany when you buy
> an approved wireless phone you are told that it is impossible to
> listen in to it. Bullsh*t. In fact it's only impossible to listen in
> with another (unmodified) wireless phone -- just get a scanner and
> you're in.

For GSM, the level of privacy for both signalling and voice is
considerable.  Just to give you an idea, encryption keys change for
each call made by the subscriber and the encryption algorithms use the
changing physical properties of the radio channel.

As a matter of fact, GSM is SO secure that several European
governments including Britain are insisting that the scrambling
algorithm ( called A5 in GSM ) be modified to allow at least
government operatives ( read "undercover eavesdroppers" ) to listen in
on suspected criminal activities. Agencies such as GCHQ, the British
government's listening post near Cheltenham and the FBI in America are
concerned that the A5 scrambling algorithm provided with the GSM
Mobile Stations is equivalent to many military systems and in fact
when exported may be adapted for military applications.

Vendors of GSM equipment are starting to run into export problems due
to the nature of the encryption / ciphering.

Although there are some industrious "scanners" out there, I dare say
that listening in on a GSM conversation will be a bit of a job.


Michael Lyman    Motorola - Iridium     Phoenix, Arizona