Encrypting voice comunications..

Mikko Rauhala mjrauhal at cc.helsinki.fi
Fri Feb 2 23:45:22 CET 2007

pe, 2007-02-02 kello 09:54 -0800, Tim Newsom kirjoitti:
> So, though possibly inefficient, we could not some how take the analog 
> audio stream, do some predictable and reversible encoding/encrypting 
> then convert into sounds again.. Like doing base64 encoding for binary 
> data..
> In that way we are still sending audio information and letting it get 
> encoded by the gsm module.

Well. Even if the hardware supports feeding the GSM chip with audio from
the SoC instead of the mic directly (does it? it would be useful for
other stuff too, but I don't really know), it would be a rather
nontrivial exercise to make an encryption transform that would properly
survive lossy GSM encoding (and two d-a-d-conversions...) and be

Analog encryption methods could be tried, but when the GSM encoding
kicks in on the encrypted data stream, it'd probably throw away a lot of
the information present, as the stream would be highly entropic. I'm not
very familiar with analog encryption though, so I can't dismiss the
possibility that it could work with some fiendishly clever scheme.

The other option would be to use digital encryption and use a soft modem
to feed data through the voice channel. Again, the GSM encoding (and
echo cancellation and whatnot that may be going on) is an obstacle, the
d-a-d conversions adding a bit. I can't personally dismiss this outright
either; it is obvious that a soft modem over GSM voice can deliver
_some_ data rates; maybe, just maybe, enough for 2kbps Speex with clever
enough algorithms (I'll be happy to hear an expert opinion either way).
Seems like anyone wishing to try has their work cut out for them,

For an immediately workable solution ("immediately", as in lacking
merely putting the already existing pieces together; no small feat
either but just "work"), there is the earlier mentioned GSM data. Which,
really, is a good choice here. Or monologue away with p-t-t (or t-t-t,
what-have-you) and gprs, confident that the voice will reach the
recipient at some point in the not too far away future :]

Mikko Rauhala   - mjr at iki.fi     - <URL:http://www.iki.fi/mjr/>
Transhumanist   - WTA member     - <URL:http://www.transhumanism.org/>
Singularitarian - SIAI supporter - <URL:http://www.singinst.org/>

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