Random digital encryption secure communication system

• US 4,341,925 A
• Filed: 04/28/1978
• Issued: 07/27/1982
• Est. Priority Date: 04/28/1978
• Status: Expired due to Term

• Current Assignee: Frosch Robert A Administrator of The National Aeronautics and Space Administration With Respect To An Invention of, George D. Doland
• Original Assignee: Frosch Robert A Administrator of The National Aeronautics and Space Administration With Respect To An Invention of, George D. Doland
• Inventors: Doland, George D., Frosch, Robert A. Administrator of the National Aeronautics and Space Administration, with respect to an invention of
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/900,841
• Time in Patent Office: 1,551 Days
• Field of Search: 325/32, 325/30, 325/65, 178/22, 178/22.16, 178/227.1, 364/717, 375/106, 375/110, 375/111, 455/26
• US Class Current: 380/262
• CPC Class Codes: H04L 2209/12 Details relating to cryptographic hardware or logic circuitry
• CPC Class Codes: H04L 9/0662 with particular pseudorandom sequence generator
• CPC Class Codes: H04L 9/12 Transmitting and receiving encryption devices synchronised or initially set up in a particular manner

Abstract

A new and improved secure communication system is provided. A product code, formed from two pseudorandom sequences of digital bits, is used to encipher or scramble data prior to transmission. The two pseudorandom sequences are periodically changed at intervals before they have had time to repeat. One of the two sequences is transmitted continuously with the scrambled data for synchronization.

In the receiver portion of the system, the incoming signal is compared with one of two locally generated pseudorandom sequences until correspondence between the sequences is obtained. At this time, the two locally generated sequences are formed into a product code which deciphers the data from the incoming signal. Provision is made to ensure synchronization of the transmitting and receiving portions of the system.

Claims

1. A secure communication receiver for receiving and decoding an encrypted digital signal, comprising:

(a) means for receiving said encrypted signal wherein said means for receiving comprises

means for forming a bit sync signal indicating bit synchronization with bit transitions in said encrypted signal;

(b) first generator means for forming a first local pseudorandom code wherein said first generator means comprises;

(1) a first digital data pseudorandom sequence generator;

(2) a second digital data pseudorandom sequence generator adapted to receive said bit sync signal and wherein said second sequence generator comprises means functioning as a shift register prior to receipt of said bit sync signal and functioning as a pseudorandom sequence generator thereafter; and

(3) a gate connecting said first and said second digital data sequence generators for serial flow of digital bits from said first to said second generators, being adapted to receive said bit sync signal and wherein said gate comprises gate means responding to said bit sync signal to block flow of digital bits from said first to said second generator;

(c) second generator means for forming a second local pseudorandom code;

(d) means for forming a local product code from said first and said second local pseudorandom codes; and

(e) decoder means for decoding said encrypted signal with said local product code.

2. A secure communication receiver for receiving and decoding an encrypted digital signal, comprising:

(a) means for receiving said encrypted signal wherein said means for receiving comprises means for forming a bit sync signal indicating bit synchronization with bit transitions in said encrypted signal;

(b) first generator means for forming a first local pseudorandom code;

(c) second generator means for forming a second local pseudorandom code wherein said second generator means comprises;

(1) a first digital data pseudorandom sequence generator;

(2) a second digital data pseudorandom sequence generator adapted to receive said bit sync signal and wherein said second sequence generator comprises means functioning as a shift register prior to receipt of said bit sync signal and functioning as a pseudorandom sequence generator thereafter; and

(3) a gate connecting said first and said second digital data sequence generators for serial flow of digital bits from said first to said second generators, being adapted to receive said bit sync signal and wherein said gate comprises gate means responding to said bit sync signal to block flow of digital bits from said first to said second generator;

(d) means for forming a local product code from said first and said second local pseudorandom codes; and

(e) decoder means for decoding said encrypted signal with said local product code.