Fourier masking analog signal secure communication system

A scrambling arrangement (10) capable of forming and transmitting a secure time domain analog signal (x.sub.s (t)) which is an encoded adaptation of an input time domain analog message signal (x.sub.a (t))

• characterized in that
• the scrambling arrangement comprises:
• a Fourier transform processor (12) capable of generating as an output a Fourier transform frequency domain signal (X.sub.a (n)) related to the input time domain analog message signal;
• scrambling means (14) capable of encoding said Fourier transform frequency domain signal produced by said Fourier transform processor to produce as an output a secure Fourier transform frequency domain signal (X.sub.s (n));
• and
• an inverse Fourier transform processor (16) capable of transforming said secure Fourier transform frequency domain signal produced by said scrambling means into the secure time domain analog communication signal (x.sub.s (t)).

A descrambling arrangement capable of receiving a secure time domain analog communication signal (x.sub.s (t)) related to a Fourier transform of a time domain analog message communication signal (x.sub.a (t)) and decoding said secure analog signal to reform said analog message communication signal

• characterized in that
• the descrambling arrangement comprises:
• a Fourier transform processor (22) capable of receiving as an input the secure time domain analog communication signal and generating as an output a secure Fourier transform frequency domain signal (X.sub.s (n)) corresponding to said secure time domain analog communication signal;
• descrambling means (24) capable of decoding said secure Fourier transform frequency domain signal generated by said Fourier transform processor to produce as an output a Fourier transform frequency domain signal (X.sub.a (n));
• and
• an inverse Fourier transform processor (26) responsive to said Fourier transform frequency domain signal produced by said descrambling means and capable of transforming said Fourier transform frequency domain signal into the time domain analog message communication signal.

A method of achieving secure transmission of a time domain analog message signal (x.sub.a (t)) comprising the steps of:

• a. scrambling said time domain analog message signal to form a secure time domain analog signal (X.sub.s (t)),
• b. transmitting the secure time domain analog signal;
• characterized in that
• the method comprises the further steps of:
• c. in performing step (a), performing the steps of:
• 1. transforming the analog message signal (x.sub.a (t)) into its associated N-length message Fourier coefficient frequency domain sequence (X.sub.a (n));
• 2. coding the result of step (c)(1) to form an N-length secure Fourier coefficient frequency domain sequence (X.sub.s (n));
• and
• 3. inverse-transforming the result of step (c)(2) to form the secure time domain analog signal (x.sub.s (t)).

A method of achieving reception of a secure analog signal (x.sub.s (t)) related to a Fourier transform of an analog message signal and recovering said analog message signal therefrom comprising the steps of:

• a. receiving the secure analog signal;
• and
• b. descrambling the received secure analog signal to recover the original analog message signal x.sub.a (t)
• characterized in that
• the method comprises the further steps of:
• c. in performing step (b), performing the steps of:
• 1. transforming the received secure analog signal (x.sub.s (t)) into its associated N-length secure Fourier coefficient sequence (X.sub.s (n));
• 2. decoding the result of step (c)(1) to recover the original N-length Fourier coefficient sequence (X.sub.a (n));
• and
• 3. inverse-transforming the result of step (c)(2) to form the analog message signal x.sub.a (t).