32N +D bit key encryption-decryption system using chaos

• US 5,751,811 A
• Filed: 11/26/1996
• Issued: 05/12/1998
• Est. Priority Date: 08/30/1995
• Status: Expired due to Fees

• Current Assignee: James J. Rouches, Ramon Sais
• Original Assignee: James J. Rouches, Larry A. Nelson, Ramon Sais
• Inventors: Nelson, Larry A., Magnotti, Joseph C.
• Primary Examiner(s): Tarcza, Thomas H.
• Assistant Examiner(s): White, Carmen D.
• Application Number:
  US08/756,047
• Time in Patent Office: 532 Days
• Field of Search: 380/28, 380/37, 380/44, 380/46, 380/42
• US Class Current: 380/28
• CPC Class Codes: H04L 9/001 using chaotic signals
• CPC Class Codes: H04L 9/0662 with particular pseudorandom sequence generator

Abstract

A cryptographic method and system based on chaos theory is provided. Unique random 64-bit binary strings generated from an iterative chaotic equation are used as logic and arithmetic operands during encryption/decryption. The random 64-bit binary strings are generated based on 4 initializer values that produce thousands of iterated values from the chaotic equation z_t+1 =Z_t² +c, where z and c are complex numbers. The 64-bit random numbers are translated into two 32-bit keys so that each 32 bits of message are encrypted/decrypted, using a bitwise logic operator such as an exclusive-or, with a unique 32-bit key for the length of the message file. For additional security, a combination of logic and arithmetic operators are used on the 32-bit keys and the 32-bit blocks of message text to produce 32N-bit blocks of ciphertext, where N=2_r and r≦2. For any set of 4 initializer values, the lifetime, n, is the number of iterations of the equation Z_t+1 =z_t² +c before divergence of the output to infinity, and the number of unique 32-bit keys is 4n, where n can be over 300,000 for a multitude of initializer values.

Claims

1. A method of encryption comprising the steps of;

a) selecting four initializer values which are used to generate n chaotic iterates from a chaotic equation, where n is the lifetime of the chaotic equation, and wherein said chaotic equation is z_t+1 =z_t² +c, where z and c are complex numbers;

b) generating two chaotic iterates from said chaotic equation;

c) converting the two chaotic iterates into a predetermined number of chaotic keys;

d) encrypting a block of plaintext message as a block of ciphertext based on one of said chaotic keys;

e) repeating step d) until a predetermined number of blocks of plaintext message have been encrypted with one each of said chaotic keys;

f) repeating steps b) through e) until the entire plaintext message is encrypted as ciphertext.

2. The method of claim 1 wherein said predetermined number of chaotic keys in step c) is four and said predetermined number of blocks of plaintext message in step e) is four.

3. The method of claim 1 wherein each chaotic iterate is of length 2L, each chaotic key is of length L, each block of plaintext message is of length L, and each block of ciphertext is of length L.

4. The method of claim 3 wherein L=32 bits.

5. The method of claim 1 wherein the step of encrypting the plaintext message comprises combining each plaintext message block and each chaotic key by an exclusive-or operation.

6. The method of claim 1 further comprising the step of decrypting the ciphertext to the plaintext message based on the chaotic keys.

7. The method of claim 6 wherein the step of decrypting the ciphertext comprises combining the ciphertext blocks and said chaotic keys by an exclusive-or operation.

8. The method of claim 1 wherein, when the number of said chaotic iterates used to encrypt said message approaches n, two of said four initializer values are incremented at step a).

9. A method of encryption comprising the steps of;

a) selecting four initializer values which are used to generate n chaotic iterates from a chaotic equation, where n is the lifetime of the chaotic equation, and wherein said chaotic equation is z_t+1 =z_t² +c, where z and c are complex numbers;

b) generating two chaotic iterates, each of length L, from said chaotic equation;

c) converting the two chaotic iterates into four chaotic keys of length L;

d) separating each of said four chaotic keys into a first portion and a second portion;

e) converting four blocks of plaintext message to four blocks of length 2L by multiplying each said block of length L of plaintext message by one of said first portions of each of said four chaotic keys;

f) separating each block of said multiplied plaintext message of length 2L into two blocks of length L;

g) encrypting four blocks of said multiplied plaintext message of length L as ciphertext based on said second portion of each of said four chaotic keys;

h) combining the ciphertext into blocks of length 2L;

i) repeating steps b) through h) until the entire plaintext message is encrypted as ciphertext.

10. The method of claim 9 wherein L=32 bits.

11. A method of encryption comprising the steps of;

a) selecting four initializer values which are used to generate n chaotic iterates from a chaotic equation, where n is the lifetime of the chaotic equation, and wherein said chaotic equation is Z_t+1 z_t² +c, where z and c are complex numbers;

b) generating two chaotic iterates from said chaotic equation;

c) converting the two chaotic iterates into four chaotic keys;

d) separating each of said chaotic keys into a first portion and a second portion;

e) converting four blocks of plaintext message into four blocks of multiplied plaintext message by multiplying each said block of plaintext message by said first portion of a specific chaotic key;

f) repeat steps b) through e) which generate four new chaotic keys which are different than all previously generated chaotic keys, each said new chaotic key first portion is multiplied with one of said four blocks of plaintext message, said plaintext message being separate from all plaintext messages previously converted, and continue step f) until all of said plaintext message is converted to multiplied plaintext;

g) separating each block of said multiplied plaintext message into two blocks;

h) encrypting each separated block of said multiplied plaintext message with said second portion of a predetermined chaotic key to produce a block of ciphertext;

i) combining consecutive blocks of ciphertext to produce an encrypted message;

j) repeating steps h) and i) until all blocks of ciphertext have been converted into encrypted messages.

12. The method of claim 11 wherein the step h) includes repeating the steps of b) through d) to regenerate the chaotic keys which are separated to produce the second portion used for said encrypting.

13. The method of claim 11 wherein each chaotic iterate is of length 2L, each chaotic key is of length L, each block of plaintext message is of length L, each block of multiplied plaintext message is of length 2L, each block of separated plaintext message is of length L, and each block of ciphertext is of length 2L.

14. The method of claim 13 wherein L=32 bits.

15. The method of claim 11 wherein the step of encrypting the multiplied plaintext message comprises combining each multiplied plaintext message block and each said second portion of each said chaotic key by an exclusive-or operation.

16. The method of claim 11 further comprising the step of decrypting the encrypted message to the plaintext message based on the chaotic keys.

17. The method of claim 13 further including the step of decrypting the encrypted message which comprises the steps of;

separating each ciphertext block of length 2L into two blocks of length L;

combining said ciphertext blocks of length L and said second portion of said chaotic keys of length L by an exclusive-or operation;

assembling the combined ciphertext and chaotic keys into blocks of length 2L;

dividing each block of length 2L by said first portion of one of said four chaotic keys to arrive at the plaintext message of length L;

repeating these steps until the entire ciphertext is decrypted to plaintext.

18. The method of claim 11 wherein, when the number of said chaotic iterates used to encrypt said message approaches n, two of said four initializer values are incremented at step a).

19. A method of encryption comprising the steps of;

a) selecting four initializer values which are used to generate n chaotic iterates from a chaotic equation, where n is the lifetime of the chaotic equation, and wherein said chaotic equation is z_t+1 =z_t² +c, where z and c are complex numbers;

b) generating chaotic iterates, each of length 2L, from said chaotic equation;

c) converting each chaotic iterate of length 2L into two chaotic keys of length L;

d) encrypting blocks of length L of plaintext message as ciphertext based on said chaotic keys; and

e) repeating steps b) through d) until the entire plaintext message is encrypted as ciphertext.

20. The method of claim 19 wherein said step b) generates two chaotic iterates, and step c) four chaotic keys.

21. The method of claim 19 wherein L=32 bits.

22. The method of claim 19 wherein the step of encrypting the plaintext message comprises combining each plaintext message block of length L and one each of said four chaotic keys by an exclusive-or operation.

23. The method of claim 19 further comprising the step of decrypting the ciphertext back to plaintext based on the chaotic keys.

24. The method of claim 23 further comprising the step of decrypting the ciphertext comprising combining each ciphertext block of length L and one each of said four chaotic keys by an exclusive-or operation.

25. The method of claim 19 wherein step d) encrypts blocks of plaintext message of length L into ciphertext blocks of length 2L.

26. The method of claim 25 wherein the step of encrypting comprises;

1) separating each of said four chaotic keys into a first portion and a second portion;

2) converting four blocks of length L of plaintext message to four blocks of length 2L by multiplying each said block of length L of plaintext message by one of said first portions of each of said four chaotic keys;

3) separating each block of length 2L into two blocks of length L;

4) encrypting four blocks of length L as ciphertext based on said second portion of each of said four chaotic keys, by combining each plaintext message block and each said second portion of each said four chaotic keys by an exclusive-or operation;

5) combining the ciphertext into blocks of length 2L.

27. The method of claim 26 including the steps of decrypting the ciphertext comprising;

separating each ciphertext block of length 2L into two blocks of length L;

combining said ciphertext blocks of length L and said chaotic keys of length L by an exclusive-or operation;

assembling the combined ciphertext and chaotic keys into blocks of length 2L;

dividing each block of length 2L by said first portion of one of said four chaotic keys to arrive at the plaintext message.

28. A system for encryption comprising;

means for selecting four initializer values which are used to generate n chaotic iterates from a chaotic equation, where n is the lifetime of the chaotic equation, and wherein said chaotic equation is z_t+1 =z_t² +c, where z and c are complex numbers;

means for generating at least one chaotic iterate from said chaotic equation;

means for converting each of said at least one chaotic iterates into two chaotic keys;

means for encrypting at least one block of plaintext message as at least one block of ciphertext based on said chaotic keys.

29. The system of claim 28 wherein said at least one chaotic iterate is of length 2L, said chaotic keys are of length L, said at least one block of plaintext message is of length L, and said at least one block of ciphertext is of length L.

30. The system of claim 28 wherein two chaotic iterates and four chaotic keys are generated.

31. The system of claim 29 wherein L=32 bits.

32. The system of claim 28 wherein means for encrypting combines at least one of said blocks of plaintext message and at least one of said chaotic keys by an exclusive-or operation.

33. The system of claim 28 including means for decrypting said at least one block of ciphertext back to at least one block of plaintext based on said chaotic keys.

34. The system of claim 33 wherein means for decrypting the ciphertext combines each said at least one block of ciphertext and at least one of said chaotic keys by an exclusive-or operation.

35. The system of claim 30 wherein each of said plaintext message blocks is of length L and is encrypted as a ciphertext block of length 2L.

36. The system of claim 35 wherein said means for encrypting comprises;

means for separating each of said four chaotic keys into a first portion and a second portion;

means for converting four blocks of length L of plaintext message into four blocks of length 2L, said means comprising multiplying each said block of length L of plaintext message by one of said first portions of each of said four chaotic keys;

means for separating each block of length 2L into two blocks of length L;

means for encrypting four blocks of length L as ciphertext based on said second portion of each of said four chaotic keys, wherein each plaintext message block and each chaotic key is combined by an exclusive-or operation; and

means for combining the ciphertext into blocks of length 2L.

37. The system of claim 35 including means for decrypting the ciphertext comprising;

means for separating each ciphertext block of length 2L into two blocks of length L;

means for combining said ciphertext blocks of length L and said chaotic keys by an exclusive-or operation;

means for assembling the combined ciphertext and chaotic keys into blocks of length 2L; and

means for dividing each block of length 2L by said first portion of one of said four chaotic keys to arrive at the plaintext message.