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Cryptographically secure communication system

  • US 4,283,602 A
  • Filed: 09/23/1968
  • Issued: 08/11/1981
  • Est. Priority Date: 06/03/1966
  • Status: Expired due to Term
First Claim
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1. A cryptographically secure communication system employed with a transmission medium having a given low frequency pass band and a predetermined bandwidth comprising:

  • a source of analog signal confined to said given pass band and said predetermined bandwidth;

    first means coupled to said source to produce amplitude sample pulses from said analog signal at a given rate related to at least twice said predetermined bandwidth, each of said sample pulses having a discrete amplitude equal to one of a predetermined number of discrete amplitude levels;

    second means to provide a first sequence of signals representing randomly and with substantially equal probability said predetermined number of discrete amplitude levels, said first sequence of signals being coincident with said sample pulses;

    third means coupled to said first means and said second means responsive to said sample pulses and said first sequence of signals to encrypt said sample pulses;

    said transmission medium;

    fourth means coupled between said third means and said transmission medium to convert said encrypted sample pulses to an encrypted analog signal confined to said given pass band and said predetermined bandwidth for propagation through said transmission medium;

    fifth means coupled to said transmission medium to produce encrypted amplitude sample pulses from said encrypted analog signal at said given rate, each of said encrypted sample pulses having a discrete amplitude equal to one of said predetermined number of discrete amplitude levels;

    sixth means synchronous with said second means to provide a second sequence of signals identical to said first sequence of signals, said second sequence of signals being coincident with said encrypted sample pulses;

    seventh means coupled to said fifth means and said sixth means responsive to said encrypted sample pulses and said second sequence of signals to decrypt said encrypted sample pulses and recover said sample pulses;

    eighth means coupled to said seventh means to convert said sample pulses to said analog signal confined to said given pass band and said predetermined bandwidth; and

    ninth means coupled to said eighth means having said given pass band and said predetermined bandwidth to utilize said analog signal.

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