From: azur@netcom.com (Steve Schear)
Date: Sun, 19 Jan 1997 16:43:27 -0800 (PST)
To: cypherpunks@toad.com
Subject: Re: GSM crypto upgrade? (was Re: Newt's phone calls)
Message-ID: <v02140b00af086e8ed0db@[10.0.2.15]>
MIME-Version: 1.0
Content-Type: text/plain


For voice calls, it is not possible to merely insert a more secure crypto
function (e.g., IDEA) inside the less secure A5 crypto, unless the GSM base
station's protocol is aware the subscriber unit is using the more secure
crypto.  Otherwise, when the GSM base station unwraps the A5 encrypted data
stream, which it assumes will contain digitized voice packets in the clear,
it will not find what its looking for and will be unable to convert the
packets to a circuit-switched voice signal.

If, as I have previously stated, the subscriber instead uses the data port
of his instrument and establishes a data link with his payload protected by
the more the secure crypto this is entirely feasible.

-- Steve


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