ENCRYPTION METHOD

• US 20110311042A1
• Filed: 10/22/2009
• Published: 12/22/2011
• Est. Priority Date: 10/23/2008
• Status: Active Grant

• Current Assignee: University of Ulster
• Original Assignee: University of Ulster
• Inventors: Cheddad, Abbas, Condell, Joan, Curran, Kevin, McKevitt, Paul
• Granted Patent: US 8,670,560 B2
• Time in Patent Office: Days
• US Class Current: 380/28
• CPC Class Codes: G06F 21/602 Providing cryptographic facilities or services
• CPC Class Codes: G06F 21/64 Protecting data integrity, e.g. using checksums, certificates or signatures
• CPC Class Codes: H04L 9/0656 Pseudorandom key sequence combined element-for-element with data sequence, e.g. one-time-pad [OTP] or Vernam's cipher
• CPC Class Codes: H04N 1/4486 using digital data encryption
• CPC Class Codes: H04N 2201/3236 Details of authentication information generation

Abstract

There is described a method of encrypting a set of 2D input data, preferably image data. The method comprises obtaining the hash value of a password and re-sizing the hash value to fir the size of the 2D input data. The re-sized data is transformed using an irreversible transform, and the output of the transform is then used to encode the 2D data.

Claims

1. A method of encrypting a set of two-dimensional (2D) input data, the method comprising the steps of

(a) providing a 2D hash array;

(b) performing a transform operation on the 2D hash array;

(c) generating a binary pseudorandom map based on the transformed 2D hash array; and

(d) generating an encrypted 2D data set by performing a logical XOR operation using the binary pseudorandom map and the bit stream version of the 2D input data.

2. The method of claim 1, wherein the 2D input data comprises an image file defined in a multi-dimensional colour space. However, the 2D input data may comprise any known file format that is capable of being represented electronically as a two-dimensional data set.

3. The method of claim 1, wherein step (d) further comprises the step of converting the XORed bit stream into grayscale values to generate an encrypted 2D data set.

4. The method of claim 1, wherein the binary pseudorandom map is generated such that:

5. The method of claim 4, wherein tho is chosen such that the probability P(f(u,v)<

thr₁)=P(f(u,v)>

thr₁).

6. The method of claim 4, wherein thr₁=0.

7. The method of claim 1, wherein said step (d) is performed such that the set of 2D input data, A, and the encrypted 2D data set, A′

, conform to the relationship;

{A−

D(A′

, Map)}≡

{Ø

}

where D(A′

,Map) is the decoding of A′ and

Map is the binary pseudorandom map.

8. The method of claim 1, wherein the transform operation comprises a Discrete Cosine Transform (DCT) and a Fast Fourier Transform (FFT).

9. The method of claim 8, wherein the transform operation comprises:

10. The method of claim 9, wherein the transform thresholding operation is:

11. The method of claim 10, wherein thr₂ is chosen such that the probability P(F(x,y)<

thr₂)=P(F(x,y)>

thr₂).

12. The method of claim 1, wherein step (a) comprises:

providing a one-dimensional (1D) hash string H(P); and

resizing the 1D hash string H(P) to a 2D hash array.

13. The method of claim 1, wherein the 2D image data set comprises an image file defined in a multi-dimensional colour space, and wherein the step of generating an encrypted 2D image data set comprises:

performing a plurality of logical XOR operations using a binary pseudorandom map and the bit stream version of each of the colour space components of the 2D image input data to generate encrypted colour space data sets; and

combining the encrypted colour space data sets to form the encrypted 2D image data set.

14. The method of claim 13, wherein steps (a) to (c) are repeated to provide a binary pseudorandom map for each colour space component of the 2D image data set.

15. The method of claim 14, wherein step (a) comprises providing an individual 2D hash array for each colour space component of the 2D image data set.

16. The method of claim 15, wherein step (a) comprises generating individual 2D hash arrays for each colour space component based on a password P, wherein said individual 2D hash arrays are based on a combination of different string reading directions and/or multiple hashing operations.

17. The method of claim 1, wherein the 2D input data comprises a 2D image data set defined in three-dimensional colour space.

18. The method of claim 17, wherein the three-dimensional colour space is RGB space.

19. The method of claim 1, wherein the method further comprises the step of resizing the encrypted 2D data set to have the same dimensions as the 2D input data.

20. The method of claim 1, wherein step (b) is performed on a permuted version of the 2D hash array.

21. The method of claim 20, wherein said permuted version of the 2D hash array is generated by performing a pseudorandom permutation operation on said 2D hash array.

22. The method of claim 1, wherein the method further comprises a post-encryption step, the step comprising:

(i) providing an element substitution map; and

(ii) performing an element substitution operation based on said element substitution map on the elements of said encrypted 2D data set to generate an element-substituted encrypted 2D data set.

23. The method of claim 22, wherein said step of providing comprises generating said element substitution map by applying a hash function to the 1D hash string H(P).

42. A method of decrypting a set of encrypted 2D data, the data encrypted according to the method of claim 1, the method comprising the steps of:

(a) providing a 1D hash string H(P);

(b) resizing the 1D hash string H(P) to a 2D hash string;

(c) performing a transform operation on the 2D hash string; and

(d) decoding the set of encrypted 2D data based on the transformed 2D hash string to provide a decrypted 2D data set.

24. A method of encrypting a set of two-dimensional (2D) input data, the method comprising the steps of:

(a) providing a one-dimensional (1D) hash string H(P);

(b) resizing the 1D hash string H(P) to a 2D hash string;

(c) performing a transform operation on the 2D hash string; and

(d) encoding the set of 2D input data to be encrypted based on the transformed 2D hash string to provide an encrypted 2D data set.

25. The method of claim 24, wherein the step of providing a 1D hash string comprises generating a 1D hash string H(P) by applying a hash function to a password P.

26. The method of claim 24, wherein step (b) includes the step of converting the 1D hash string H(P) into the binary equivalent of H(P).

27. The method of claim 24, wherein the step (d) of encoding the set of 2D input data to be encrypted comprises:

(i) generating a binary pseudorandom map based on the transformed 2D hash string; and

(ii) generating an encrypted 2D data set by performing a logical XOR operation using the binary pseudorandom map and the bit stream version of the 2D input data.

28. The method of claim 24, wherein the bit stream of the 1D hash string H(P) is resized to a 2D matrix.

29. The method of claim 28, wherein the bit stream of the 2D input data is resized to have the dimension of 8×

(Π

(M,N)), where M×

N is the dimension of the bit stream of the 2D input data.

30. The method of claim 28, wherein the 2D matrix has a fixed dimension of 8×

35.

31. The method of claim 24, wherein the 2D input data comprises an image file defined in a multi-dimensional colour space, and wherein the step of generating an encrypted 2D image data set comprises:

performing a plurality of logical XOR operations using a binary pseudorandom map and the bit stream version of each of the colour space components of the 2D image input data to generate encrypted colour space data sets; and

combining the encrypted colour space data sets to form the encrypted 2D image data set.

32. The method of claim 31, wherein steps (a) to (c) are repeated to provide a binary pseudorandom map for each colour space component of the 2D image data set.

33. The method of claim 32, wherein step (a) comprises providing an individual 2D hash array for each colour space component of the 2D image data set.

34. The method of claim 33, wherein step (a) comprises generating individual 2D hash arrays for each colour space component based on a password P, wherein said individual 2D hash arrays are based on a combination of different string reading directions and/or multiple hashing operations.

35. The method of claim 34, wherein three different 1D hash strings are generated, the hash strings comprising H({right arrow over (P)}), H() and H(H()), wherein the arrows indicate the string reading directions.

36. The method of claim 31, wherein the step of providing a 1D hash string comprises generating a 1D hash string H(P) by applying a hash function to a password P, and wherein a different password is provided for each individual colour space component.

37. The method of claim 24, wherein step (c) is performed on a permuted version of the 2D hash string.

38. The method of claim 37, wherein said permuted version of the 2D hash string is generated by performing a pseudorandom permutation operation on said 2D hash string.

39. The method of claim 38, wherein said pseudorandom permutation is based on the output of a pseudo-random number generator, wherein the seed for the pseudo-random number generator is selected from one of the following:

the 1D hash string H(P);

or an unhashed 1D password P.

40. The method of claim 24, wherein the method further comprises a post-encryption step, the step comprising:

(iii) providing an element substitution map based on the 1D hash string H(P); and

(iv) performing an element substitution operation based on said element substitution map on the elements of said encrypted 2D data set to generate an element-substituted encrypted 2D data set.

41. The method of claim 40, wherein said step of providing comprises generating said element substitution map by applying a hash function to the 1D hash string H(P).

43. A computer program product comprises a computer readable medium on which computer instructions are stored which when executed in a computing device are arranged to encrypt a set of two-dimensional (2D) input data by:

(a) providing a 2D hash array;

(b) performing a transform operation on the 2D hash array;

(c) generating a binary pseudorandom map based on the transformed 2D hash array; and

(d) generating an encrypted 2D data set by performing a logical XOR operation using the binary pseudorandom map and the bit stream version of the 2D input data.

44. An encryption system for encrypting a set of two-dimensional (2D) input data, the system comprising:

(a) an input device operable to receive a set of 2D input data;

(b) an output device operable to output an encrypted 2D data set; and

(c) a processor, the processor operable to;

a. provide a one-dimensional (1D) hash string H(P);

b. resize the 1D hash string H(P) to a 2D hash string;

c. perform a transform operation on the 2D hash string; and

d. encode the set of 2D input data to be encrypted based on the transformed 2D hash string to provide an encrypted 2D data set.

45. An encryption system for encrypting a set of two-dimensional (2D) input data, the system comprising:

(a) an input device operable to receive a set of 2D input data;

(b) an output device operable to output an encrypted 2D data set; and

(c) a processor, the processor operable to;

a. provide a 2D hash array;

b. perform a transform operation on the 2D hash array;

c. generate a binary pseudorandom map based on the transformed 2D hash array; and

d. generate an encrypted 2D data set by performing a logical XOR operation using the binary pseudorandom map and the bit stream version of the 2D input data.

46. A computer program product comprises a computer readable medium on which computer instructions are stored which when executed in a computing device are arranged to decrypt a set of two-dimensional (2D) input data by:

(a) providing a 1D has string H(P);

(b) resizing the 1D hash string H(P) to a 2D hash string;

(c) performing a transform operation on the 2D hash string; and

(d) decoding the set of encrypted 2D data based on the transformed 2D hash string to provide a decrypted 2D data set.