IP: Re: Cypherpunks break GSM digital cell phone encryption

[Dave Farber <farber () cis upenn edu>]

From: Sky Dayton <sky () earthlink net>


Comment: The Time article originally forwarded to IP appeared lacking in
specifics (vintage Time), and it wasn't clear if they had hacked into a
conversation, or just managed to clone the account. This seems to clear it
up; the conversation is secure, but the phone account can be hijacked. At
least that's how I'm reading it.


Hats off to Time for again sensationalizing a simple issue, a la their
"Cyberporn" and "Web of Death" cover stories. I think I summarized it well
in my bLink column:


        http://www.earthlink.net/blink/vault/issue14/skywriting.html


Sky



--


> > Delivered-To: ip-sub-1 () majordomo pobox com
> > X-Sender: farber () linc cis upenn edu
> > Date: Fri, 17 Apr 1998 08:25:36 -0400
> > To: ip-sub-1 () majordomo pobox com
> > From: Dave Farber <farber () cis upenn edu>
> > Subject: IP: Re: Cypherpunks break GSM digital cell phone encryption )from
> >  RISKS)
> > Sender: owner-ip-sub-1 () majordomo pobox com
> > Reply-To: farber () cis upenn edu
> >
> > Date: Thu, 16 Apr 1998 09:53:26 +1000
> > From: Stewart Fist <fist () zip com au>
> > Subject: Re: Cypherpunks break GSM digital cell phone encryption
> >
> > Declan McCullagh <declan () well com> quotes TIME Magazine, April 20, 1998
> > as reporting: " Now crooks scanning the airwaves can remotely tap into a
call
> > and duplicate the owner's digital ID. "We can clone the phones," brags Marc
> > Briceno, who organized the cracking. His advice: manufacturers should
> stick to
> > publicly vetted codes that a bunch of geeks can't crack in their spare
> time." 
> > My understanding is that they managed to crack the code on the SIM or smart
> > card, not any radio-transmitted information.  They repeatedly asked the card
> > to identify itself, and so cracked it by brute force.
> >
> > The article also says: ``What was even more intriguing than the security
> > threat, however, was that cracking the code yielded a tantalizing hint
that a
> > digital key used by GSM may have been intentionally weakened during the
> design
> > process to permit government agencies to eavesdrop on cellular telephone
> > conversations.''
> >
> > This has been known for years.  The use of GSM in Australia, for instance,
> was
> > blocked on the day of the official launch because the security and police
> > services wanted an easier code to break.  At that time, I understand, they
> > just switched encryption off. This was also widely reported in Europe at the
> > time, and openly admitted.
> >
> > The original A5 encryption was promoted as being "NATO level security" which
> > was a bit of overkill for a mobile phone that is probably going to be used
> > with an insecure wireline link, and often used in public places.
> >
> > Now it appears that they've cut the 64-bit key down to an effective
54-bit by
> > adding trailing zeros to make it easier to crack.  It would still be a
pretty
> > healthy sort of encryption even at this level however.
> >
> > Stewart Fist, 70 Middle Harbour Road, Lindfield, 2070, N.S.W, Australia 
> > +61 2 9416 7458  http://www.theaustralian.com.au/techno/columns/fist.htm
> --
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