From: "Dave Emery" <die@pig.die.com>
Date: Thu, 1 Feb 1996 10:11:18 +0800
To: jk@digit.ee (Jyri Kaljundi)
Subject: Re: encrypted cellphones
In-Reply-To: <Pine.SOL.3.91.960131172957.4630D-100000@jaramillo.digit.ee>
Message-ID: <9602010113.AA07886@pig.die.com>
MIME-Version: 1.0
Content-Type: text/plain


Juri Kaljudi wrote: 

> 
> On Wed, 31 Jan 1996, Bill Stewart wrote:
> 
> > providers don't.  The GSM phones used in much of the world have encryption,
> > but it's apparently not very strong.

	As the A5 algorithm has so far not been publically disclosed, no
one outside of the spook community really knows if has a backdoor or
what computational effort might be involved in brute forcing it.  One
can certainly suppose that there was a lot of pressure to weaken it,
but whether that was accomplished by installing trapdoors or simply by making
special purpose hardware brute forcers simple, fast, and cheap is not known.

> 
> I would say GSM security is still better than nothing. The problem is of 
> course that only tha radio link is encrypted, not the connection out into 
> public telephone network.

	I have seen news stories about some shady "spy-shop" type
companies in England who are selling microwave receivers capable
of intercepting and decoding the microwave backhaul links that connect
most GSM cell sites to the mobile switching offices.   Apparently even
some supposedly secure GSM systems use unencrypted backhauls which can
be relatively easily intercepted by someone with the right gear 
from places near enough the towers to have a line of sight view
of them.

						Dave Emery
						die@die.com