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speech encryption

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faezehdn

New Member
hi everyone.
I need to encrypt speech that is being transmitted over FM (20kHz)
I can encrypt speech signal while its analog (is there any IC i can use ?)
or convert it to digital and then encrypt it.
the method using for encryption should be simple.
any idea where should I start ? any reliable source ?
which one do you think would be easier digital or analog ?
I googled it and know the basics, but I don't know where to start.
thanks everyone.
 

crutschow

Well-Known Member
Most Helpful Member
The simpler the encryption, the less secure it is.
How secure do you need, just from the casual eavesdropper or from a dedicated hacker / the government?
 

audioguru

Well-Known Member
Most Helpful Member
Many years ago I made an audio scrambler with an MC1496 balanced modulator/demodulator IC, a crystal oscillator, a counter and a couple of switched capacitor lowpass filter ICs. It was for a wireless FM microphone and made single sideband suppressed carrier signals. The high audio frequencies became low frequencies and the low audio frequencies became high frequencies and voice words were completely unintelligible. The descrambler used a very similar circuit and tits sound was perfect. It worked so well that my prototype was sold as the finished product.
 

MikeMl

Well-Known Member
Most Helpful Member

faezehdn

New Member
Many years ago I made an audio scrambler with an MC1496 balanced modulator/demodulator IC, a crystal oscillator, a counter and a couple of switched capacitor lowpass filter ICs. It was for a wireless FM microphone and made single sideband suppressed carrier signals. The high audio frequencies became low frequencies and the low audio frequencies became high frequencies and voice words were completely unintelligible. The descrambler used a very similar circuit and tits sound was perfect. It worked so well that my prototype was sold as the finished product.
well done,I've read about frequency domain voice scrambler.
any idea where should I start ? any article I can use ?
 

davenn

Active Member
another way is just do a frequency inversion low audio tones become high and visa versa
makes the resulting audio unintelligible
 

Sinedup

Member
Maybe you could try (pre-carrier) ADC (CH1), XOR bits with fixed-pattern (CH2). Then DAC.
Then at audio of receiver, ADC again, XOR (scrambled audio) bits (CH1) with identical fixed-pattern (CH2).
Then DAC to recover analog audio.
This works in theory when simulated (Profilab Expert).
Never constructed it in "real world". ..no need.
 
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