Encryption method and decryption method based on optical chaos and image quotient-remainder preprocessing

Abstract

The present invention discloses an image encryption method and a decryption method based on optical chaos and image quotient-remainder preprocessing. The encryption method includes: S1, generating synchronous optical chaos signals by using three slave lasers with the same parameters and constructing a dynamic key set; S2, performing quotient-remainder preprocessing on the original image; S3, encrypting the image processed in step S2 by using the optical chaos signals generated in step S1 and the dynamic key set. The present invention utilizes the optical chaos characteristics of the laser, the reduction processing of the image pixel values, and multiple encryption and watermark operations, so that the image pixel values are more concentrated and the distribution is more uniform, greatly improving the security of the ciphertext image.

Description

Technical Field

[0001] The present invention belongs to the technical field of image encryption and decryption, and particularly relates to an encryption and decryption method based on optical chaos and image quotient-remainder preprocessing. Background Art

[0002] With the development of modern society and the improvement of technology, the emergence of new media with images and videos as carriers has greatly enriched people's daily lives. However, in recent years, due to privacy leakage, individuals, organizations or institutions have continuously suffered losses, and people's requirements for the security of image information transmission have become increasingly high. Since images usually have large sizes and strong spatial correlations, traditional text encryption methods are not applicable to images. In 1998, Fridrich J. first applied chaos theory to image encryption, which attracted the attention of many scholars, and many image encryption schemes based on chaotic systems have been proposed. However, due to various algorithm attacks by eavesdroppers, such as statistical attacks, differential attacks, etc., some encryption algorithms cannot meet the security requirements, especially when transmitting extremely important information images such as medical, military, and aviation, the images must achieve sufficient security. Therefore, in order to strengthen the protection of image security, researchers are still constantly working hard on this road. Summary of the Invention

[0003] In order to solve the problem of insufficient security in existing image encryption algorithms, the present invention provides an encryption method and a decryption method based on optical chaos and quotient-remainder preprocessing of the original image.

[0004] To achieve the above object, the present invention adopts the following technical solutions:

[0005] An encryption method based on optical chaos and image quotient-remainder preprocessing, comprising the following steps:

[0006] S1. Generate synchronous optical chaos signals using three slave lasers with the same parameters, and construct its dynamic key set;

[0007] S2. Before encrypting the image, first perform quotient-remainder preprocessing on the original image.

[0008] S3. Use the laser chaos sequence and key set generated in step S1 to perform multiple operations such as encryption, watermarking, and diffusion on the processed image.

[0009] As a preferred solution, in step S1, the light emitted by the master laser is reflected by a mirror to three slave lasers to generate three synchronous optical chaos signals.

[0010] As a preferred solution, in step S2, in the original image, for pixel values from 0 to 64, take the remainder with respect to 2; for pixel values from 99 to 144, take the remainder with respect to 3; for pixel values from 196 to 255, take the remainder with respect to 4; keep the remaining pixel values unchanged; use the same method to perform the division operation on the image, thereby obtaining two images, one is the division image after taking the remainder of the image, and the other is the remainder image after taking the division of the image; the specific processing process is as follows:

[0011]

[0012]

[0013] Among them, P is the plaintext image, P1 and P2 are the images of taking the remainder and the division respectively; (i, j) is the coordinate of the image pixel, 0 < i < 256, 0 < j < 256; P(i, j) represents the pixel value of the pixel point.

[0014] As a preferred solution, in step S3, randomly extract n (n = 3) values from the laser chaotic signal output by the first slave laser as the encryption key for image scrambling.

[0015] As a preferred solution, in step S3, three-step encryption is performed, specifically as follows:

[0016] First-step encryption: Use the extracted encryption key to encrypt the division image, obtaining the encrypted image 1; the key is sent to the receiving end by combining with the chaos generated by the first slave laser.

[0017]

[0018] Among them, K j is the encryption key, K m is the first three bits of the chaos sequence of the first slave laser SL1, and k is the key.

[0019] Second-step encryption: Intercept the first 256 * 256 sequence in the chaos generated by the first slave laser, and combine it with the remainder image to obtain the encrypted image 2;

[0020] P4 = mod(K x , 250) + P2(4)

[0021] Among them, P4 is the encrypted image 2, K x is the first 256 * 256 items of the chaos sequence of the first slave laser SL1, and P2 is the image after taking the remainder of the original image; the pixel value of P2 is between 0 and 3 (including 0 and 3).

[0022] Step 3 Encryption: Use the encrypted image 2 to perform steganography on the encrypted image 1, and through the diffusion process of the pseudo-random sequence, obtain the final ciphertext image.

[0023] P5 = mod(P4, 64) + P3 (5)

[0024] Among them, P5 is the ciphertext image, and P3 and P4 are the encrypted image 1 and the encrypted image 2 respectively; the pixel value of P3 is between 0 and 192 (including 0 and 192).

[0025] As a preferred solution, in the first step of encryption, two-dimensional Arnold scrambling is adopted, and the encrypted key is used to encrypt the quotient-taking image, and the size of the original image is 256*256.

[0026] As a preferred solution, in the third step of encryption, the GF(17) domain multiplication operation is used to diffuse the encrypted image.

[0027] As a preferred solution, as shown in Equation 6 and Equation 7, in the GF(17) domain multiplication, the gray value (0-255) of the input image pixel points is divided into the high 4 bits and the low 4 bits. The values of the high 4 bits and the low 4 bits are both 0-15. When looking up the table, they are converted into 1-16, and the lookup table result is subtracted by the original high 4 bits and low 4 bits.

[0028]

[0029]

[0030] Among them, S is the pseudo-random sequence, P is the original image, C is a 256*256 zero matrix, and C(0) is zero; the subscript H represents the high 4 bits of the data, and the subscript L represents the low 4 bits of the data. Equation (6) represents the forward diffusion, and Equation (7) is the reverse diffusion process of the image.

[0031] As a preferred solution, after the encryption in step S3, through the chaos masking technology, that is, the ciphertext image is converted into optical information and superimposed with the chaos generated by the first slave laser (as shown in Equation 8), and sent to the third slave laser through a long-distance optical fiber.

[0032] K = K m1 +K s (8)

[0033] Among them, K is the optical information after chaos masking, and K m1 、K s are the chaos generated by SL1 and the ciphertext converted into optical information respectively.

[0034] The present invention also discloses a decryption method based on optical chaos and image quotient-remainder preprocessing. Based on the above-mentioned decryption method of optical chaos and image quotient-remainder preprocessing, the decryption method specifically includes the following steps:

[0035] S4. Receive the information sent by the sending end, and obtain the key and the remainder image of the original image by using the chaotic sequence generated by the second slave laser.

[0036] S5. The third slave laser receives the information of the encrypted ciphertext and uses the information obtained in S4 to restore the image.

[0037] As a preferred solution, in step S4, the second slave laser receives the optical information of the encrypted image 2 sent by the sending end, and uses the generated chaotic carrier to restore the remainder image of the original image; and cracks the key combined with the chaotic sequence of the first slave laser (as shown in Equation 9);

[0038]

[0039] where k is the key, K j is the encrypted key, and K n is the first three bits of the chaotic sequence of the second slave laser SL2.

[0040] As a preferred solution, step S5 is specifically as follows:

[0041] S5.1. The third slave laser receives the optical information sent by the sending end SL1, and uses the synchronized chaos to decrypt the ciphertext image;

[0042] S5.2. Use the encrypted image 2 obtained by the second slave laser to perform a watermark removal operation on the ciphertext image first;

[0043] S5.3. Use the key obtained from the second slave laser to perform the inverse transformation of the cat map on the watermark-removed encrypted image to restore the quotient image of the original image;

[0044] S5.4. By combining and adding with the remainder image restored by the second slave laser, the original image is restored.

[0045] As a preferred solution, to meet the synchronization of chaos, the parameters of the three slave lasers are the same, that is, they have the same structure, and the signal wavelengths generated by the three slave lasers are all 1550 nm.

[0046] Compared with the prior art, the beneficial effects of the present invention are:

[0047] 1. Compared with traditional chaotic systems such as the Logistic map and Lorenz chaos, the laser chaotic system of the present invention has more complex dynamic characteristics, lower power consumption and larger bandwidth.

[0048] 2. The preprocessing of the present invention and the multi-layer encryption of the image make the image pixel values more concentrated and the distribution more uniform, break the correlation between pixels, and greatly improve the security of the encrypted image. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Figure 1 is the encryption and decryption flow chart of the present invention based on optical chaos and image quotient-remainder preprocessing.

[0050] Figure 2 is the block diagram of the encryption and decryption system of the present invention based on optical chaos and image quotient-remainder preprocessing.

[0051] Figure 3 The following is the specific process of the preprocessing of the specific example image of the present invention: (a) plaintext image; (b) image after taking the quotient; (c) image after taking the remainder; (d) encrypted image 1 after encryption with a random key; (e) encrypted image 2 after encryption with a random chaotic sequence; (f) encrypted image 3 after steganography of image 2 on image 1; (g) encrypted image after diffusion. DETAILED DESCRIPTION OF THE INVENTION

[0052] In order to more clearly illustrate the embodiments of the present invention, the specific embodiments of the present invention will be described below with reference to the accompanying drawings. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other drawings can be obtained according to these drawings, and other embodiments can be obtained.

[0053] As Figure 1 shown, an image encryption method and a decryption method based on optical chaos and image quotient-remainder preprocessing in an embodiment of the present invention are described with reference to Figure 2 , and the optical chaos image encryption transmission system includes a receiving end and a transmitting end; the specific steps of the encryption and decryption methods are as follows:

[0054] Step S1: Generate optical chaos signals by using three slave lasers, and randomly select three values from the chaotic sequence of SL1 as keys. And in order to satisfy the synchronization of chaos, the parameters of the three slave lasers (SL1, SL2, SL3) are the same, that is, they have the same structural characteristics, and the generated signal wavelengths are all 1550 nm.

[0055] Specifically, the light emitted by the master laser ML is reflected by the mirror M into the laser cavity, disturbing the interaction between carriers and photons in the laser, and then injected into three slave lasers (SL1, SL2, SL3) with the same parameters respectively to generate three chaotically synchronized optical chaos signals.

[0056] Step S2: Before encrypting the image, first perform quotient-remainder preprocessing on the original image with a size of 256*256.

[0057] Specifically, before image encryption, some processing is first performed on P (the original image). For pixel values from 0 to 64 in the image, the remainder of division by 2 is taken; for pixel values from 99 to 144, the remainder of division by 3 is taken; for pixel values from 196 to 255, the remainder of division by 4 is taken; and the remaining pixel values remain unchanged. After performing the same method for the division operation on the image, two images are obtained. One is the division image after taking the remainder of the image, and the other is the remainder image after taking the division of the image. The specific processing process is as follows:

[0058]

[0059]

[0060] Among them, P is the plaintext image, P1 and P2 are the images of taking the remainder and division respectively; (i, j) is the coordinate of the image pixel, 0 < i < 256, 0 < j < 256; P(i, j) represents the pixel value of the pixel point.

[0061] Step S3: Use the optical chaos sequence generated in Step S1 and the key to perform multiple operations such as encryption, watermarking, and diffusion on the image processed in Step S2.

[0062] Specifically:

[0063] The first encryption: Adopt Arnold scrambling, use the key to encrypt the division image, and obtain the encrypted image 1; the key is sent to the receiving end by combining with the chaos generated by the first slave laser.

[0064]

[0065] Among them, K j is the encryption key, K m is the first three digits of the chaos sequence of the first slave laser SL1, and k is the key.

[0066] The second encryption: Intercept the first 256 * 256 sequence from the chaos generated by the first slave laser SL1, combine it with the remainder image, and obtain the encrypted image 2, as shown in the following formula:

[0067] P4 = mod(K x , 250) + P2 (13)

[0068] Among them, P4 is the encrypted image 2, K x is the first 256 * 256 items of the chaos sequence of the first slave laser SL1, and P2 is the image after taking the remainder of the original image; the pixel value of P2 is between 0 and 3 (including 0 and 3).

[0069] Third - step encryption: Use the encrypted image 2 to perform steganography on the encrypted image 1, as shown in Equation 14:

[0070] P5 = mod(P4, 64)+P3 (14)

[0071] Where P5 is the ciphertext image, and P3 and P4 are the encrypted image 1 and the encrypted image 2 respectively; the pixel value of P3 is between 0 and 192.

[0072] Finally, through the diffusion process of the pseudo - random sequence, the final ciphertext image is obtained. The ciphertext image is converted into optical information, combined with the chaos generated by the first slave laser SL1 through the chaos masking technology, and sent to the receiving end.

[0073] The following is the decryption process:

[0074] Step S4: Receive the information sent by the sending end, and use the chaos sequence generated by the second slave laser to obtain the key and the remainder image of the original image.

[0075] Specifically, the second slave laser SL2 receives the optical information of the encrypted image 2 sent by the sending end, uses the generated chaotic carrier to restore the remainder image of the original image, and cracks the key combined with the chaos sequence of the first slave laser, as shown in Equation 15:

[0076]

[0077] Where k is the key, K j is the encrypted key, and K n is the first three bits of the chaos sequence of the second slave laser SL2.

[0078] Step S5: The third slave laser receives the information of the encrypted ciphertext and uses the information obtained in S4 to restore the image.

[0079] Specifically, first, the third slave laser receives the optical information sent by the sending end SL1, uses the synchronized chaos to decrypt the ciphertext image; secondly, uses the encrypted image 2 obtained from the second slave laser to perform a watermark - removal operation on the ciphertext image; then uses the key obtained from the second slave laser to perform the inverse transformation of the cat map on the watermark - removed encrypted image to restore the quotient image of the original image. Finally, by combining and adding it with the remainder image restored by the second slave laser, the original image is restored.

[0080] In summary, the image encryption method and decryption method of the present invention based on optical chaos and image quotient - remainder pre - processing greatly improve the security of image transmission, and solve problems such as high attenuation, low complexity, and high cost of traditional chaos. In addition, the encryption and transmission system has a short running time, high speed, and good encryption performance, and can meet people's needs for image confidentiality.

[0081] It should be noted that the above is the preferred embodiment of the present invention, which does not limit the protection scope of the present invention. For those of ordinary skill in the art, according to the research ideas provided by the present invention, there will be improvements in the specific design solutions, and these changes should also be regarded as within the protection scope of the present invention.

Claims

1. An encryption method based on optical chaos and image quotient-remainder preprocessing, characterized in that, It includes the following steps: S1. Generate synchronous optical chaotic signals using three slave lasers with the same parameters and construct a dynamic key set; S2. Perform quotient-remainder preprocessing on the original image; S3. Use the optical chaotic signals generated in step S1 and the dynamic key set to encrypt the image processed in step S2 multiple times; in step S2, in the original image, for pixel values from 0 to 64, perform modulo 2 operation; for pixel values from 99 to 144, perform modulo 3 operation; for pixel values from 196 to 255, perform modulo 4 operation; and keep the remaining pixel values unchanged; use the same method to perform quotient operation on the image, thus obtaining two images, one is the quotient image after taking the remainder of the image, and the other is the remainder image after taking the quotient of the image; the specific processing process is as follows: Where P is the plaintext image, and P1 and P2 are the remainder and quotient images respectively; (i, j) are the coordinates of the image pixels, 0 < i < 256, 0 < j < 256; P(i, j) represents the pixel value of the pixel point; In step S3, three-step encryption is performed, specifically as follows: The first-step encryption: Use the extracted encryption key to encrypt the quotient image to obtain encrypted image 1; the key is sent to the receiving end by combining with the chaos generated by the first slave laser; Among them, K j is the encrypted key, and K m is the first three bits of the chaotic sequence of the slave laser, and k is the key; The second-step encryption: Intercept the first 256*256 sequence from the chaos generated by the first slave laser and combine it with the remainder image to obtain encrypted image 2; P4 = mod(K x , 250) + P2 (4) Among them, P4 is the encrypted image 2, and K x is the first 256*256 items of the chaotic sequence of the slave laser, and P2 is the image obtained by taking the remainder of the original image; the pixel value of P2 is between 0 and 3, including 0 and 3; The third-step encryption: Use encrypted image 2 to perform steganography on encrypted image 1 and perform diffusion processing on it through a pseudo-random sequence to obtain the final ciphertext image; P5 = mod(P4, 64) + P3 (5) Where P5 is the ciphertext image, and P3 and P4 are encrypted image 1 and encrypted image 2 respectively; the pixel value of P3 is between 0 and 192, including 0 and 192.

2. The encryption method based on optical chaos and image quotient-remainder preprocessing according to claim 1, characterized in that, In step S1, the light emitted by the master laser is reflected by the mirror to three slave lasers to generate three synchronous optical chaotic signals.

3. The encryption method based on optical chaos and image quotient-remainder preprocessing according to claim 1, characterized in that, In step S3, randomly extract n values from the laser chaotic signal output by the first slave laser as the encryption key for image scrambling, n = 3.

4. The encryption method based on optical chaos and image quotient-remainder preprocessing according to claim 1, characterized in that, In the first-step encryption, two-dimensional Arnold scrambling is adopted, and the encryption key is used to encrypt the quotient image, and the size of the original image is 256*256; In the third-step encryption, GF(17) domain multiplication operation is used to diffuse the encrypted image; as shown in formulas (6) and (7), in GF(17) domain multiplication, the gray value of the input image pixel point is divided into the high 4 bits and the low 4 bits, and the gray value is from 0 to 255; the values of the high 4 bits and the low 4 bits are both from 0 to 15, and when performing table lookup processing, they are converted to 1 to 16, and the table lookup result subtracts the original high 4 bits and low 4 bits by 1 bit; Where formula (6) represents the forward diffusion, and formula (7) is the reverse diffusion process of the image.

5. The encryption method based on optical chaos and image quotient-remainder preprocessing according to any one of claims 1-4, characterized in that, After encryption in step S3, through the chaos masking technology, that is, the ciphertext image is converted into optical information and superimposed with the chaos generated by the first slave laser, as shown in formula (8), and sent to the third slave laser through a long-distance optical fiber; K = K m1 + K s (8) Among them, K is the optical information after chaotic masking, K m1 , K s are respectively the chaos generated by the first slave laser and the ciphertext converted into optical information.

6. A decryption method based on optical chaos and image quotient-remainder preprocessing, based on the encryption method according to any one of claims 1-5, characterized in that, The specific steps of the decryption method are as follows: S4. Receive the information sent by the sending end, and obtain the key and the remainder image of the original image by using the chaotic sequence generated by the second slave laser; S5. The third slave laser receives the information of the encrypted ciphertext and uses the information obtained in S4 to restore the image.

7. The decryption method based on optical chaos and image quotient-remainder preprocessing according to claim 6, wherein, In step S4, the second slave laser receives the optical information of the encrypted image 2 sent by the sending end, and uses the generated chaotic carrier to restore the remainder image of the original image; and crack the key combined with the chaotic sequence of the first slave laser, as shown in formula (9); where k is the secret key, and K j is the encrypted secret key, and K n is the first three bits of the chaotic sequence of the second slave laser SL2.

8. The decryption method based on optical chaos and image quotient-remainder preprocessing according to claim 7, wherein, The specific steps of step S5 are as follows: S5.

1. The third slave laser receives the optical information sent by the first slave laser and decrypts the ciphertext image by using the synchronized chaos; S5.

2. Use the encrypted image 2 obtained by the second slave laser to perform the operation of removing the watermark from the ciphertext image; S5.

3. Use the key obtained from the second slave laser to perform the inverse transformation of the cat map on the encrypted image with the watermark removed, and the quotient image of the original image is restored; S5.

4. By combining and adding with the remainder image restored by the second slave laser, the original image is restored.

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