Encrypted GSM phone

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Sylvain Munaut 246tnt at gmail.com
Mon Apr 9 22:04:14 UTC 2012


> I have been just wondering... would it be possible to use your project
> as a base for DIY encrypted cellphone? My idea is that if I could get
> hold to output data after voice is encoded by GSM EFR codec, I might
> just easily encrypt this digital stream using AES128 and build trully
> encrypted cellphone.

Yes, the idea has been raised many times before.

The problem is that in a lot of network the voice is going to be
decompressed in the network, transferred as PCM and then recompressed.

> Where does actual "analog voice from microphone to digital data"
> conversion happends? In a layer1 that runs in a chip, or layer23 that
> runs on a PC? If it would be in layer23, encrypting a data stream with
> AES 128 whould be doable, am I missing something?

It's actually done lower than layer1, inside the DSP itself.
It is however possible to send custom data (taken from the PC
microphone for eg.). That's what the LCR integration does.



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