Encrypting voice comunications..

Mikko J Rauhala mjrauhal at cc.helsinki.fi
Fri Feb 2 18:13:12 CET 2007

On pe, 2007-02-02 at 09:06 -0800, Tim Newsom wrote:
> If we have access to the mic and speakers while a call is in process, 
> and we have the ability to record conversations etc...  Where does the 
> processor sit in that chain?  Can we consume the voice, encrypt it and 
> feed an encrypted datastream back out to the gsm module which would 
> transmit it and another neo1973 user could receive the stream, process 
> through decryption and play out?

No. The GSM processor does its own audio de- and encoding, and its
connection to the audio i/o is analog, as reported by LaF0rge on irc a
while back (any misunderstanding is probably mine if present, though).
We can get at the audio via the a/d converters, but not do anything
really fancy directly.

Thus, I refer you to my last mail; make a GSM data call (phone-to-phone
if possible, if not, both dial out and arrange the call via some
server), transmit encrypted Speex stream. There would still be a bit of
latency, but you would get reserved bandwidth at least.

This of course costs extra. Probably one of the principal reasons why
GSM chips don't like you sending your own digital data over voice
calls. :]

Mikko J Rauhala <mjrauhal at cc.helsinki.fi>
University of Helsinki

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