Coding method and system with enhanced security

• US 4,225,935 A
• Filed: 08/30/1977
• Issued: 09/30/1980
• Est. Priority Date: 08/30/1977
• Status: Expired due to Term

• Current Assignee: L-3 Communications Corporation (L3Harris Technologies, Inc.)
• Original Assignee: Sperry Corporation (Unisys Corporation)
• Inventors: Zscheile, John W. Jr., Spencer, Billie M.
• Primary Examiner(s): Birmiel, Howard A.
• Application Number:
  US05/830,274
• Time in Patent Office: 1,127 Days
• Field of Search: 364/717, 325/32, 331/78, 178/22
• US Class Current: 708/253
• CPC Class Codes: H04K 1/00 Secret communication
• CPC Class Codes: H04L 9/0668 producing a non-linear pseudorandom sequence

Abstract

A coding system produces a code with enhanced acquisition security by generating a plurality of linear component codes, C₁, C₂, . . . C_n, combining the component codes in accordance with a modulo-2 addition rule to form a linear first composite code, nonlinearizing the first composite code to form a nonlinear second composite code, time delaying the component codes, C₁, C₂, . . . C_n-1, and combining the time delayed codes with the nonlinear second composite code in accordance with a Boolean majority voting rule to form a nonlinear acquisition composite code. Acquisition of the nonlinear acquisition composite code is achieved by generating a plurality of linear reference component codes, R₁, R₂, . . . R_n, that correlate respectively with the linear acquisition component codes, C₁, C₂, . . . C_n, combining the reference component codes in accordance with the modulo-2 addition rule to form a linear third composite code, nonlinearizing the third composite code to form a nonlinear fourth composite code, time delaying the reference component codes, R₁, R₂ , . . . R_n-1, correlating the time delayed codes with the nonlinear acquisition composite code by shifting the phases of the time delayed codes, and correlating the fourth composite code with the acquisition composite code by shifting the phase of the reference component code, R_n.

Claims

1. A method of producing a code with enhanced acquisition security, comprising the steps of:

generating a plurality of linear component codes, C₁, C₂, . . . C_n ;

combining said linear component codes to form a linear first composite code in accordance with a first composite rule of such a character that said first composite code does not correlate with said component codes;

nonlinearizing said first composite code to form a nonlinear second composite code; and

combining said linear component codes, C₁, C₂, . . . C_n-1, with said nonlinear second composite code to form a nonlinear acquisition composite code in accordance with a second composite rule of such a character that at least one of said component codes correlates with said acquisition composite code.

2. A method of producing a code with enhanced acquisition security, comprising the steps of:

generating a plurality of linear component codes, C₁, C₂, . . . C_n ;

combining said linear component codes to form a linear first composite code in accordance with a first composition rule of such a character that said first composite code does not correlate with said component codes;

nonlinearizing said first composite code to form a nonlinear second composite code;

time delaying said component codes, C₁, C₂, . . . C_n-1 ; and

combining said delayed codes, C₁, C₂, . . . C_n-1, with said nonlinear second composite code to form a nonlinear acquisition composite code in accordance with a second composition rule of such a character that at least one of said delayed codes correlates with said acquisition composite code.

3. A method of producing a code with enhanced acquisition security, comprising the steps of:

generating a plurality of linear component codes, C₁, C₂, . . . C_n ;

combining said linear component codes in accordance with a modulo-2 addition rule to form a linear first composite code;

nonlinearizing said first composite code by applying the same to an encrypter operating in a decrypt mode to form a nonlinear second composite code;

time delaying said component codes, C₁, C₂, . . . C_n-1 ; and

combining said time delayed codes, C₁, C₂, . . . C_n-1, with said nonlinear second composite code in accordance with a Boolean majority voting rule to form a nonlinear acquisition composite code.

4. A system for producing a code with enhanced acquisition security, comprising:

means for generating a plurality of linear component codes, C₁, C₂, . . . C_n ;

means for combining said linear component codes to form a linear first composite code in accordance with a first composition rule of such a character that said first composite code does not correlate with said component codes;

means for nonlinearizing said first composite code to form a nonlinear second composite code; and

means for combining said linear component codes, C₁, C₂, . . . C_n-1, with said nonlinear second composite code to form a nonlinear acquisition composite code in accordance with a second composite rule of such a character that at least one of said component codes correlates with said acquisition composite code.

5. A system for producing a code with enhanced acquisition security, comprising:

means for generating a plurality of linear component codes, C₁, C₂, . . . C_n ;

means for combining said linear component codes to form a linear first composite code in accordance with a first composition rule of such a character that said first composite code does not correlate with said component codes;

means for nonlinearizing said first composite code to form a nonlinear second composite code;

means for time delaying said component codes, C₁, C₂, . . . C_n-1 ; and

means for combining said delayed codes, C₁, C₂, . . . C_n-1, with said nonlinear second composite code to form a nonlinear acquisition composite code in accordance with a second composition rule of such a character that at least one of said delayed codes correlates with said acquisition composite code.

6. The system for producing a code as recited in claim 5, wherein:

said first composition rule is a modulo-2 addition rule;

said nonlinearizing means comprises an encrypter operating in a decrypt mode to which said first composite code is applied to form said nonlinear second composite code; and

said second composition rule is a Boolean majority voting rule.

7. A coding method for communication between a transmitter and a receiver with enhanced security, comprising the steps of:

(I) at the transmitter,

(a) generating a plurality of linear acquisition component codes, C₁, C₂, . . . C_n,

(b) combining said acquisition component codes to form a linear first composite code in accordance with a first composition rule of such a character that said first composite code does not correlate with said component codes,

(c) nonlinearizing said first composite code to form a nonlinear second composite code,

(d) combining said linear component codes, C₁, C₂, . . . C_n-1, with said nonlinear second composite code to form a nonlinear acquisition composite code in accordance with a second composition rule of such a character that at least one of said component codes correlates with said acquisition composite code, and

(e) transmitting said nonlinear acquisition composite code; and

(II) at the receiver,

(a) receiving said nonlinear acquisition composite code,

(b) generating a plurality of linear reference component codes, R₁, R₂, . . . R_n, that correlate respectively with said linear acquisition component codes, C₁, C₂, . . . C_n,

(c) combining said reference component codes to form a linear third composite code in accordance with said first composition rule,

(d) nonlinearizing said third composite code in a manner identical to that of said (I,c) nonlinearizing step to form a nonlinear fourth composite code,

(e) correlating said reference component codes, R₁, R₂, . . . R_n-1, with said nonlinear acquisition composite code by shifting the phases of said reference component codes, R₁, R₂, . . . R_n-1, and

(f) correlating said nonlinear fourth composite code with said nonlinear acquisition composite code by shifting the phase of the remaining reference component code, R_n.

8. The coding method as recited in claim 7, wherein:

said first composition rule is a modulo-2 addition rule; and

said second composition rule is a Boolean majority voting rule.

9. The coding method as recited in claim 7, wherein:

said (I,c) nonlinearizing step comprises applying said linear first composite code to an encrypter operating in a decrypt mode to form said nonlinear second composite code; and

said (II,d) nonlinearizing step comprises applying said linear third composite code to an encrypter operating in a decrypt mode to form said nonlinear fourth composite code.

10. The coding method as recited in claim 7, wherein:

said (I,d) combining step comprises time delaying said acquisition component codes, C₁, C₂, . . . C_n-1, and combining said delayed codes with said nonlinear second composite code to form said nonlinear acquisition composite code in accordance with said second composition rule; and

said (II,e) correlating step comprises time delaying said reference component codes, R₁, R₂, . . . R_n-1, by the same amount that said acquisition component codes, C₁, C₂, . . . C_n-1, are time delayed and correlating said delayed reference component codes with said nonlinear acquisition composite code.

11. The coding method as recited in claim 7, further comprising the steps of:

(II) at the receiver,

(g) combining said linear reference component codes, R₁, R₂, . . . R_n-1, with said nonlinear fourth composite code in accordance with said first composition rule to form a nonlinear fifth reference composite code, and

(h) correlating said nonlinear fifth composite code with said nonlinear acquisition composite code;

(I) at the transmitter,

(f) combining said linear acquisition component codes, C₁, C₂, . . . C_n-1, with said nonlinear second composite code in accordance with said first composition rule to form a nonlinear data-carrying composite code, and

(g) transmitting said nonlinear data-carrying composite code; and

(II) at the receiver,

(i) receiving said nonlinear data-carrying composite code, and

(j) correlating said nonlinear fifth reference composite code with said nonlinear data-carrying composite code.

12. The coding method as recited in claim 11, wherein:

said first composition rule is a modulo-2 addition rule; and

said second composition rule is a Boolean majority voting rule.