Aaron,
the usual problems with end-to-end encryption in GSM come into play:
* as the voice path is not transparent but transcoded any number of times
in the core network, you cannot simply encrypt the codec frames but gqwill
have to initiate a CSD ('modem') connection.
* not many networks support it anymore
* calling rates are more expensive
* you immediately leave a visible trail, since nobody else uses CSD
And no, neither is the ARM7 fast enough for any crypto, nor do we implement
CSD at all.
--
- Harald Welte <laforge(a)gnumonks.org>
http://laforge.gnumonks.org/
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