Re: cryptophone ideas

[Phil Karn <karn@qualcomm.com>]

>How hard is it to reprogram the DSP that comes with a cellular
>phone right now? I've never opened one up. Can you just unsolder
>a rom, read it, insert your own code for DH key exchange, add
>some encryption, burn a new ROM and have a secure phone? 

Also, it is not sufficient to incorporate encryption merely into the
cellular phone itself. You need the cooperation of the base station,
at least if you want to interoperate with an ordinary telephone on the
land side of your connection.

Now it would be possible to provide your own encryption on an
end-to-end basis using a data (as opposed to voice) bearer service
from the carrier, but this would require the person you call to have
compatible equipment (vocoder, modem, encryption routines, keys, etc).

Phil