> I am interested in making a PIC based project in which I need to encrypt
> voice. The voice is encrypted for transmission using a UHF radio.
> Basically the person speaks into the microphone normally, the PIC samples
> the analog data from the microphone at a minimum rate of 8kHz, XOR's it
> with a preset 'key' and converts it back to analog for transmission. At
> the other end the opposite is done. My question is does you run of the
> mill ADC0831 8-bit ADC have what it takes to sample a voice signal?

The various responses you've received have all missed the most fundamental
problem: the individual bits coming out of the receiver's ADC are going to
bear only a vague resemblance to the bits going into the transmitter's DAC,
due to signal strength variation, quantization error, etc.  Therefore, no
bit-based encryption has any chance of being decrypted by the receiver, as
long as you're using an analog signal.  Things would be different if you
transmitted the signal in digital form (using frequency-shift keying,
perhaps), but then you'd hardly need to use any encryption to keep people
from listening in...

My understanding is that analog voice scramblers work by splitting up the
signal into four or so frequency bands, then shifting them so that they end
up at a different set of non-overlapping frequencies.  Doing this in the
digital domain would require FFTs or similar techniques: I'm not
experienced enough with PICs yet to say whether this is practical to do in
real time.
        Jason Harper