(keitai-l) Re: Roaming

From: Ben Hutchings <ben.hutchings_at_roundpoint.com>
Date: 10/12/01
Message-ID: <20011012175449.H11136@zzumbouk.i.decadentplace.org.uk>
On Fri, Oct 12, 2001 at 06:49:42PM +0900, Benjamin Kowarsch wrote:
<snip> 
> What's interesting about the "visited network charges" model is that a 
> network does not rely on any other network to support the scheme (at 
> least that's the case with ZEBRA). The network that deploys wins a 
> competitive advantage in their country by fetching business from 
> tourists. On the other hand, they have no guarantee that if they hold 
> back that another network elsewhere or one of their competitors will not 
> deploy either.
<snip>

If I understand the GSM authentication and encryption protocols correctly
then it is impossible for a visited network to authenticate a visiting
handset or even to generate the correct keystreams for encryption and
decryption without the cooperation of the home network.  (They could do a
weak kind of authentication by using the same challenge every time and
checking that the response matches the one received when the account was
created, but that doesn't solve the keystream problem.)  So a network
operator could threaten to withdraw such cooperation from other operators if
they use ZEBRA.

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Received on Fri Oct 12 19:43:16 2001