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speech encryption

Discussion in 'Radio and Communications' started by faezehdn, Apr 1, 2017.

  1. faezehdn

    faezehdn New Member

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    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.
     
  2. Ian Rogers

    Ian Rogers Super Moderator Most Helpful Member

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    One thread is enough!!
     
  3. crutschow

    crutschow Well-Known Member Most Helpful Member

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    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?
     
  4. dave

    Dave New Member

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  5. audioguru

    audioguru Well-Known Member Most Helpful Member

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    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.
     
  6. MikeMl

    MikeMl Well-Known Member Most Helpful Member

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  7. faezehdn

    faezehdn New Member

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    just from the casual eavesdropper. I just need it to work right
     
  8. faezehdn

    faezehdn New Member

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    it's my end of the year project.
     
  9. faezehdn

    faezehdn New Member

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    well done,I've read about frequency domain voice scrambler.
    any idea where should I start ? any article I can use ?
     
  10. davenn

    davenn Active Member

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

    Sinedup New Member

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    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.
     
  12. BobW

    BobW Active Member

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