Image encryption algorithm for preventing ciphertext tampering attack

Abstract

The invention belongs to the technical field of image encryption, and discloses an image encryption algorithm for preventing ciphertext tampering attack, which comprises the following steps of: acquiring a to-be-encrypted image embedded with a watermark, and constructing an improved cross-hybrid coupling mapping lattice chaotic system according to a cross-coupling mapping lattice; generating a fixed secret key as a first secret key, and performing global scrambling on the to-be-encrypted image based on an improved cross-hybrid coupling mapping lattice chaotic system in combination with the first secret key to obtain a first scrambled image; performing bit plane separation on the first scrambling image to obtain a first separated image and a second separated image; respectively encrypting the first separated image and the second separated image to obtain a first encrypted image and a second encrypted image; and constructing a final encrypted image based on the first encrypted image and the second encrypted image. According to the technical scheme, the tampering attack resistance is improved, and a powerful guarantee is provided for safe transmission and storage of image data.

Description

Technical Field

[0001] The invention belongs to the technical field of image encryption, and in particular relates to an image encryption algorithm that is resistant to ciphertext tampering attacks. Background Art

[0002] With the continuous emergence of numerous image encryption algorithms, some limitations of the permutation-diffusion model encryption algorithm have become increasingly apparent. First, most existing encryption algorithms use a "one-time key" to resist differential attacks, usually using a hash function to process the plaintext image and generate a key. However, the one-time key encryption method has two significant disadvantages: first, whenever the plaintext image changes, a new key must be transmitted to the receiver, which increases the burden on the receiver and the risk of key leakage during transmission; second, encryption through multiple rounds of diffusion increases the complexity of the algorithm, thereby extending the encryption and decryption time. Third, the current image encryption algorithm lacks a mechanism to protect the encrypted image from tampering. It is difficult to determine whether the encrypted image is subject to tampering attacks during storage or transmission, and there are security risks when using the image. Summary of the invention

[0003] The purpose of the present invention is to provide an image encryption algorithm that is resistant to ciphertext tampering attacks, so as to solve the problems existing in the above-mentioned prior art.

[0004] To achieve the above object, the present invention provides an image encryption algorithm that is resistant to ciphertext tampering attacks, comprising:

[0005] Acquire an image to be encrypted, wherein the image to be encrypted is a plaintext image embedded with a watermark;

[0006] According to the cross-coupled mapping lattice, an improved cross-hybrid coupled mapping lattice chaotic system is constructed;

[0007] Generate a fixed key as a first key, and globally scramble the image to be encrypted based on an improved cross-hybrid coupled mapping lattice chaotic system combined with the first key to obtain a first scrambled image;

[0008] Performing bit plane separation on the first scrambled image to obtain a first separated image and a second separated image;

[0009] Encrypting the first separated image and the second separated image respectively to obtain a first encrypted image and a second encrypted image;

[0010] A final encrypted image is constructed based on the first encrypted image and the second encrypted image.

[0011] Optionally, obtaining the image to be encrypted includes:

[0012] A plaintext image is obtained, and a binary watermark is embedded in the plaintext image according to a watermarking technology to obtain the image to be encrypted.

[0013] Optionally, embedding a binary watermark in the plaintext image according to a watermarking technology specifically includes:

[0014] Performing Arnold transformation on the plaintext image to obtain a transformed plaintext image;

[0015] The transformed plaintext image is subjected to discrete wavelet transform and inverse discrete wavelet transform in sequence to obtain the image to be encrypted.

[0016] Optionally, the improved cross-hybrid coupling mapping lattice chaotic system is specifically:

[0017]

[0018] In the formula, represents the chaotic value of the ith grid at time n, p and q are random parameters, is the logistic mapping, θ n is the coupling function.

[0019] Optionally, based on the improved cross-hybrid coupled mapping lattice chaotic system combined with the first secret key, the image to be encrypted is globally scrambled, specifically including:

[0020] Inputting the first secret key into an improved cross-hybrid coupling mapping lattice chaotic system to obtain a first chaotic sequence;

[0021] The image to be encrypted is globally scrambled based on the first chaotic sequence combined with a row-column alternating shift algorithm to obtain a first scrambled image.

[0022] Optionally, performing bit plane separation on the first scrambled image to obtain a first separated image and a second separated image specifically includes:

[0023] The first scrambled image is subjected to bit plane decomposition, and the upper four bit planes are reconstructed into a first separated image, and the lower four bit planes are reconstructed into a second separated image.

[0024] Optionally, encrypting the first separated image and the second separated image respectively includes:

[0025] The second chaotic sequence is generated based on the improved cross-hybrid coupling mapping lattice chaotic system;

[0026] Performing odd-even splitting scrambling and bidirectional diffusion on the first split image based on the second chaotic sequence to obtain a first encrypted image;

[0027] Performing a SHA-512 hash operation on the first encrypted image to obtain a second secret key;

[0028] Inputting the second secret key into the improved cross-hybrid coupling mapping lattice chaotic system to obtain a third chaotic sequence;

[0029] The second split image is subjected to odd-even splitting scrambling and bidirectional diffusion based on the third chaotic sequence to obtain a second encrypted image.

[0030] Optionally, constructing a final encrypted image based on the first encrypted image and the second encrypted image specifically includes:

[0031] The first encrypted image and the second encrypted image are subjected to bit plane separation and combination to obtain a final encrypted image.

[0032] The technical effects of the present invention are:

[0033] The present invention modifies some parameters of the original chaotic system into a more complex chaotic system, so that it has more complex dynamic characteristics, better ergodicity and randomness, and is more suitable for application in encryption algorithms;

[0034] The present invention uses a fixed key. Unlike the traditional one-time key method, the present invention uses a fixed key. Combined with the proposed encryption algorithm, the method effectively meets the avalanche effect;

[0035] The present invention combines watermark technology and proposes a new image encryption algorithm, which has the ability to resist tampering attacks. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0037] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0038] Figure 1 is an encryption flow chart in an embodiment of the present invention;

[0039] Figure 2 Schematic diagram of a global scrambling algorithm in an embodiment of the present invention;

[0040] Figure 3 Schematic diagram of the parity splitting scrambling algorithm in an embodiment of the present invention;

[0041] Figure 4 is a schematic diagram of a bidirectional diffusion algorithm in an embodiment of the present invention;

[0042] Figure 5 Schematic diagram of encryption of the first to fourth plaintext images in an embodiment of the present invention; wherein, Figure 5 (a) is the first plaintext image in the embodiment of the present invention. Figure 5 (b) is the second plaintext image in the embodiment of the present invention. Figure 5 (c) is the third plaintext image in the embodiment of the present invention. Figure 5 (d) is the fourth plaintext image in the embodiment of the present invention. Figure 5 (e) is the encrypted image corresponding to the first plaintext image in the embodiment of the present invention. Figure 5 (f) is the encrypted image corresponding to the second plaintext image in the embodiment of the present invention. Figure 5 (g) is the encrypted image corresponding to the third plaintext image in the embodiment of the present invention. Figure 5 (h) is the encrypted image corresponding to the fourth plaintext image in the embodiment of the present invention;

[0043] Figure 6 Schematic diagram of histogram analysis in an embodiment of the present invention; wherein, Figure 6 (a) is a histogram of the first plaintext image in an embodiment of the present invention. Figure 6 (b) is a histogram of the second plaintext image in an embodiment of the present invention. Figure 6 (c) is a histogram of the third plaintext image in the embodiment of the present invention. Figure 6 (d) is a histogram of the fourth plaintext image in the embodiment of the present invention. Figure 6 (e) is a histogram of the encrypted image corresponding to the first plaintext image in the embodiment of the present invention, Figure 6 (f) is a histogram of the encrypted image corresponding to the second plaintext image in the embodiment of the present invention. Figure 6 (g) is a histogram of an encrypted image corresponding to the third plaintext image in an embodiment of the present invention. Figure 6 (h) is a histogram of an encrypted image corresponding to the fourth plaintext image in an embodiment of the present invention;

[0044] Figure 7 Schematic diagram of anti-ciphertext tampering attack in an embodiment of the present invention; wherein, Figure 7 (a) is a normal ciphertext image in an embodiment of the present invention, Figure 7 (b) is a comparison diagram of the watermark extracted from the normal ciphertext image and the original watermark in the embodiment of the present invention. Figure 7 (c) is the decrypted image corresponding to the normal ciphertext image in the embodiment of the present invention. Figure 7 (d) is a ciphertext image after being tampered with in an embodiment of the present invention. Figure 7 (e) is a comparison diagram of the watermark extracted from the ciphertext image after being tampered with and the original watermark in an embodiment of the present invention. Figure 7 (f) is the decrypted image corresponding to the ciphertext image after being tampered with in the embodiment of the present invention. DETAILED DESCRIPTION

[0045] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0046] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0047] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those of ordinary skill in the art generally understood by the present invention. Although the present invention describes only preferred methods, any method similar or equivalent to that described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods related to the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0048] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present application description and examples are exemplary only.

[0049] The words “include,” “including,” “have,” “contain,” etc. used in this article are open-ended terms, meaning including but not limited to.

[0050] It should be noted that, in the absence of conflict, the embodiments and features in the embodiments of the present application can be combined with each other. The present application will be described in detail below with reference to the accompanying drawings and in combination with the embodiments.

[0051] Embodiment 1

[0052] like Figure 1 - Figure 7As shown, in this embodiment, an image encryption algorithm that is resistant to ciphertext tampering attacks is provided, including: obtaining an image to be encrypted, wherein the image to be encrypted is a plaintext image embedded with a watermark; constructing an improved cross-hybrid coupling mapping lattice chaotic system according to a cross-coupling mapping lattice; generating a fixed key as a first key, and based on the improved cross-hybrid coupling mapping lattice chaotic system combined with the first key, globally scrambling the image to be encrypted to obtain a first scrambled image; performing bit plane separation on the first scrambled image to obtain a first separated image and a second separated image; encrypting the first separated image and the second separated image respectively to obtain a first encrypted image and a second encrypted image; and constructing a final encrypted image based on the first encrypted image and the second encrypted image.

[0053] This embodiment constructs an improved cross-hybrid coupled mapping lattice chaotic system, which has a larger range and better dynamic characteristics than the original cross-coupled mapping lattice. By combining watermarking technology, our method solves the challenge of detecting whether the image has been tampered with during storage or transmission in encrypted form. In addition, we replaced the traditional one-time key with a fixed key. Using this fixed key, a chaotic sequence is generated for global permutation of the image. Then, bit plane separation is performed, where the upper four bit planes are combined into an image for encryption. The encrypted image then generates a new key, which is used to encrypt the lower four bit planes. Finally, the two encrypted images are re-combined in bit planes. Experimental results show that the proposed algorithm has robust encryption performance, can effectively resist various attacks, and is also tamper-proof.

[0054] The overall steps include:

[0055] S1: Based on the cross-coupled mapping lattice, an improved cross-hybrid coupled mapping lattice chaotic system is constructed;

[0056] S2: using a fixed secret key to obtain the initial value of the chaotic system, iteratively improving the cross-hybrid coupling mapping lattice chaotic system to obtain a chaotic sequence; the fixed secret key is pre-set by the sender and sent to the receiver through the channel;

[0057] S3: Preprocess the plaintext image and use watermark technology to embed the watermark into the plaintext image to make the image tamper-proof;

[0058] S4: To prevent the correlation between the bit levels of the plaintext image, the chaotic sequence is used to globally scramble the plaintext image;

[0059] S5: Separate the scrambled image into bit planes, combine the upper four bit planes into an image, and perform odd-even splitting scrambling and bidirectional diffusion algorithm on the new image;

[0060] S6: Perform SHA-512 operation on the encrypted new image to obtain a new secret key, and re-iterate the chaotic system to obtain a new chaotic sequence;

[0061] S7: combine the lower four bit planes into an image, and perform the same scrambling and diffusion algorithm on the image;

[0062] S8: Re-separating and combining the encrypted upper four-bit plane image and the lower four-bit plane image to form a final encrypted image.

[0063] S9: Separate the ciphertext image into bit planes again, decrypt them separately and finally form a decrypted image.

[0064] S10: Extract the watermark, and determine whether the ciphertext image has been tampered with by comparing the extracted watermark with the original watermark.

[0065] This embodiment modifies some parameters of the original chaotic system into a more complex chaotic system, so that it has more complex dynamic characteristics, better ergodicity and randomness, and is more suitable for application in encryption algorithms; this embodiment uses a fixed key, which is different from the traditional one-time key method. This embodiment will use a fixed key, combined with the proposed encryption algorithm, which effectively meets the avalanche effect; this embodiment combines watermark technology to propose a new image encryption algorithm, which has the ability to resist tampering attacks.

[0066] The application of chaos theory in the field of image encryption is not only one of the most commonly used methods, but also one of the most effective methods. Chaos theory has the characteristics of pseudo-randomness, unpredictability, and high sensitivity to initial conditions and parameters, and is particularly suitable for image encryption. This embodiment improves the original cross-coupled mapping lattice chaotic system and proposes an improved cross-coupled mapping lattice chaotic system, which solves the shortcomings of the original chaotic system such as insufficient traversal range and insufficient randomness, has better dynamic performance, and is more suitable for encryption algorithms.

[0067] The bit plane separation algorithm is a commonly used method at present. Different operations are performed on different planes to disrupt the association between different levels. This algorithm uses a fixed secret key to first disrupt the association between pixels through global scrambling, and then uses bit plane separation to combine the upper four bit planes into an image for encryption. The encrypted image is then processed using a hash function to obtain a new secret key, and the image composed of the lower four bit planes is encrypted. Finally, the two encrypted images are re-combined by bit planes to form the final encrypted image.

[0068] The specific steps of this embodiment are as follows:

[0069] Constructing an improved cross-hybrid coupled mapping lattice: According to the cross-coupled mapping lattice chaotic system shown in formula (1), an improved cross-hybrid coupled mapping lattice chaotic system is constructed as shown in formula (2).

[0070]

[0071] Where e is the coupling coefficient, is a logical mapping, μ is a branching parameter, and the logical mapping has chaotic properties only when 3.5699456<μ≤4.

[0072]

[0073] in, represents the chaotic value of the i-th grid at time n, and mod represents the remainder function.

[0074] Formula (1) is a commonly used cross-coupled mapping lattice chaotic system, but its randomness and ergodicity are not good enough; Formula (2) is an improved tent-logic cross-mixed coupling mapping lattice. The parameter e in formula (1) is changed to a tent-logic mapping with stronger randomness, and some new parameters are added to make the chaotic characteristics of formula (2) better. n+ 1 is:

[0075]

[0076] Formula (3) is a tent-logic chaotic system, which is used to replace the parameter e in formula (1) to make the parameters of formula (2) more random, where r represents the coupling coefficient between the logical mapping and the tent mapping; Formula (4) is a method for generating parameters p and q, and their values ​​are fixed between 1 and L, where L is the number of grids; Formula (5) is a method for generating matrix A, where a, b, c and d are random Fibonacci numbers. These two formulas can make p and q more random.

[0077] In the formula, n represents time, k represents the number of grids, k∈[1,L], L is the number of grids, and the grids indexed with k+1 and k-1 are the adjacent grids of the kth grid, and their boundary conditions are specified as follows:

[0078]

[0079] Generation of keys and chaotic sequences:

[0080] Step 1: Convert the fixed key into a binary sequence h1.

[0081] Step 2: Use the function K(i)=bin2dec(h1(i:i+8)) / (2^16) to get K(i).

[0082] Step 3: Use formula (6) to obtain the secret key key(i), where i ranges from 1 to L+2 and L is the number of grids.

[0083] key(i)=mod(K(i)+K(2*i)+K(3*i)+K(4*i),1) (6)

[0084] Step 4: Use formula (7) to calculate the subkey r and θ0 are assigned values.

[0085]

[0086] Where θ0 is the initial value of formula (3), r is the coupling coefficient of formula (3), is the initial value of formula (2).

[0087] Step 5: Substitute the subkey obtained in step 5 into the improved tent-logic cross-hybrid coupling mapping lattice system, and iterate the improved cross-hybrid coupling mapping lattice chaotic system. times, and discarding the first s1 iterations, we get a length of of chaotic sequences.

[0088] Watermark embedding:

[0089] Step 1: For an N×N watermark image, the formula for performing Arnold transform n iterations is as follows:

[0090]

[0091] Step 2: In order to process the plaintext image using a two-level discrete wavelet transform (DWT), the watermark is chosen to be embedded in the LL2 subband. In this subband, N×N coefficients are randomly selected to embed the binary watermark information, which is controlled by the following formula:

[0092] Z=mod(ca,N) (9)

[0093]

[0094] ca represents the randomly selected 2-DWT coefficient, W represents the scrambled binary watermark information, N represents the height or width of the watermark image, and ca′ represents the coefficient after watermark embedding.

[0095] Step 3: Perform an inverse 2-DWT transform on the coefficients after watermark embedding to obtain the image embedded with the watermark.

[0096] Image encryption:

[0097] Step 1: Assume that the size of the plaintext image is M×M, divide the sequence obtained after inputting the fixed secret key into sequences R1 and R2 of size M, and process R1 and R2 using formulas (11) and (12);

[0098] R1(i)=mod(floor(R1(i)×10 15 ),M) (11)

[0099] R2(i)=mod(floor(R2(i)×10 15 ),M) (12)

[0100] Where M is the length or width of the square plaintext image.

[0101] Step 2: Use sequences R1 and R2 combined with the row-column alternating shift algorithm to globally scramble the plaintext image P.

[0102] Step 3: After scrambling the image P, perform bit plane decomposition. Reconstruct the upper four bit planes into image G, and reconstruct the lower four bit planes into image T, and resize each bit plane to half the size of the original image.

[0103] Step 4: Mapping the lattice chaotic system via iteratively improved cross-hybrid coupling times, and discard the first s1 iterations, resulting in a length of Chaotic sequence R3;

[0104] Step 5: Process the chaotic sequence R3 using formula (13):

[0105] SI(i)=mod(floor(R3(i)×10 15 ),M×M / 4) (13)

[0106] Among them, mod() is the remainder function, and floor() is the floor function.

[0107] Step 6: Convert the image into a one-dimensional sequence and process it using formula (14):

[0108] swap(G(i),G(i+M×M / 4)) (14)

[0109] Where swap() is the exchange function, 1≤i≤M×N / 4.

[0110] Step 7: Calculate the intermediate value temp:

[0111] temp=mod((i-1)+SI(i),M×M / 4)+1 (15)

[0112] Where 1≤i≤M×N / 4.

[0113] Step 8: Based on the value of SI, use formula (16) to perform the exchange again to obtain the scrambled image G′.

[0114]

[0115] Where 1≤i≤M×N / 4.

[0116] Step 9: Mapping the lattice chaotic system via iteratively improved cross-hybrid coupling times, and discard the first s2 iterations, resulting in a length of Chaotic sequence R4;

[0117] Step 10: Sort the chaotic sequence R4:

[0118] [~, RI4] = sort(R4) (17)

[0119] Among them, sort() is the sorting function, ~ represents the sorted vector of sequence R4, and RI4 represents the index of each element in ~ corresponding to the element in R4.

[0120] Step 11: Randomly select a point e and start the bidirectional diffusion of the image from this point according to formula (18):

[0121]

[0122] Where G′ is the scrambled image and C1 is the diffused image.

[0123] Step 12: After image G is subjected to parity splitting scrambling and bidirectional diffusion, the encrypted image C1 is obtained. Formula (19) is used to obtain a new secret key for encrypting image T.

[0124] keyb=SHA-512(C1) (19)

[0125] Step 13: Perform the same encryption operation (steps 5-13) on image T to obtain encrypted image C2.

[0126] Step 14: Separate the encrypted image C1 of G and the encrypted image C2 of T by bit planes and recombine them to obtain the final encrypted image C.

[0127] As attached Figure 5 As shown, this embodiment selects 4 images with a size of 512×512. The encryption algorithm of this embodiment can be used to obtain encrypted images. It is obvious that no useful information can be obtained at all, and the image information can be well protected.

[0128] Histograms can represent the distribution of pixel values. Figure 6The following are histograms of four images, where 6(a)-6(d) are histograms of the first to fourth plaintext images, and 6(e)-6(h) are histograms of the corresponding ciphertext images, where the horizontal axis is the pixel value, fixed between 0 and 255, and the vertical axis is the number of pixel values. Obviously, the distribution of plaintext pixel values ​​is extremely irregular. If an attacker knows this pattern, he may be able to brute force the plaintext image; but after being processed by the encryption algorithm of this embodiment, it is obvious that the distribution of each pixel value is relatively uniform, indicating that the ciphertext image covers the pixel distribution pattern of the plaintext image very well.

[0129] Image decryption:

[0130] Step 1: Decompose the ciphertext image into the upper four-bit ciphertext image C1 and the lower four-bit ciphertext image C2.

[0131] Step 2: Use the SHA-512 algorithm to process the ciphertext image C1 and obtain the secret key key-b.

[0132] Step 3: Use a fixed secret key to perform inverse processing of bidirectional diffusion and inverse processing of parity splitting scrambling on the ciphertext image C1 to obtain image G, and use the secret key key-b to perform inverse processing of bidirectional diffusion and inverse processing of parity splitting scrambling on the ciphertext image C2 to obtain image T.

[0133] Step 4: Re-combine the image G and the image T in bit planes to obtain the image P′.

[0134] Step 5: Use the fixed secret key to perform the inverse process of global scrambling on image P′ to obtain the plaintext image P.

[0135] Watermark extraction and tampering identification of ciphertext images:

[0136] Step 1: Perform a two-level discrete wavelet transform on the decrypted image, select the coefficient ca′ from the low-frequency coefficients, and then use formula (20) to extract the watermark information from the coefficients.

[0137] Z = mod(ca′, N) (20)

[0138]

[0139] in is the extracted watermark information, N represents the height or width of the watermark image, and ca′ represents the coefficient after watermark embedding.

[0140] Step 2: The original watermark information can be obtained by performing inverse Arnold transform.

[0141] Step 3: When the extracted watermark information is completely consistent with the original watermark, it means that the ciphertext image has not been tampered with, otherwise the ciphertext image has been tampered with.

[0142] Figure 7 The diagram of the anti-tampering attack is shown in Figure 7(a), where 7(a) is a normal ciphertext image and 7(d) is a ciphertext image after being tampered with. They are decrypted separately, and 7(c) and 7(f) are their decrypted images. Since the human eye cannot see the difference between the two images, it is impossible to determine whether the ciphertext image has been tampered with. However, it can be determined by analyzing the watermark. The NC value represents the accuracy of comparing the extracted watermark with the original watermark. The NC value of 7(b) is 1, which means that the extracted watermark is exactly the same as the original watermark, indicating that the ciphertext image has not been tampered with. The NC value of 7(e) is 0.73126, which means that the watermark cannot be completely extracted, indicating that the ciphertext image has been tampered with.

[0143] The above is only a preferred specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. An image encryption algorithm that is resistant to ciphertext tampering attacks, characterized in that: include: Acquire an image to be encrypted, wherein the image to be encrypted is a plaintext image embedded with a watermark; According to the cross-coupled mapping lattice, an improved cross-hybrid coupled mapping lattice chaotic system is constructed; Generate a fixed key as a first key, and globally scramble the image to be encrypted based on an improved cross-hybrid coupled mapping lattice chaotic system combined with the first key to obtain a first scrambled image; Performing bit plane separation on the first scrambled image to obtain a first separated image and a second separated image; Encrypting the first separated image and the second separated image respectively to obtain a first encrypted image and a second encrypted image; A final encrypted image is constructed based on the first encrypted image and the second encrypted image.

2. The image encryption algorithm for preventing ciphertext tampering attacks according to claim 1 is characterized in that: Get the image to be encrypted, including: A plaintext image is obtained, and a binary watermark is embedded in the plaintext image according to a watermarking technology to obtain the image to be encrypted.

3. The image encryption algorithm for preventing ciphertext tampering attacks according to claim 2 is characterized in that: Embedding a binary watermark in the plaintext image according to the watermark technology specifically includes: Performing Arnold transformation on the plaintext image to obtain a transformed plaintext image; The transformed plaintext image is subjected to discrete wavelet transform and inverse discrete wavelet transform in sequence to obtain the image to be encrypted.

4. The image encryption algorithm for preventing ciphertext tampering attacks according to claim 1 is characterized in that: The improved cross-hybrid coupled mapping lattice chaotic system is specifically: In the formula, represents the chaotic value of the ith grid at time n, p and q are random parameters, is the logistic mapping, θ n is the coupling function.

5. The image encryption algorithm for preventing ciphertext tampering attacks according to claim 1 is characterized in that: Based on the improved cross-hybrid coupling mapping lattice chaotic system and the first secret key, the image to be encrypted is globally scrambled, specifically including: Inputting the first secret key into an improved cross-hybrid coupling mapping lattice chaotic system to obtain a first chaotic sequence; The image to be encrypted is globally scrambled based on the first chaotic sequence combined with a row-column alternating shift algorithm to obtain a first scrambled image.

6. The image encryption algorithm for preventing ciphertext tampering attacks according to claim 1 is characterized in that: Performing bit plane separation on the first scrambled image to obtain a first separated image and a second separated image specifically includes: The first scrambled image is subjected to bit plane decomposition, and the upper four bit planes are reconstructed into a first separated image, and the lower four bit planes are reconstructed into a second separated image.

7. The image encryption algorithm for preventing ciphertext tampering attacks according to claim 1 is characterized in that: Encrypting the first separated image and the second separated image respectively includes: The second chaotic sequence is generated based on the improved cross-hybrid coupling mapping lattice chaotic system; Performing odd-even splitting scrambling and bidirectional diffusion on the first split image based on the second chaotic sequence to obtain a first encrypted image; Performing a SHA-512 hash operation on the first encrypted image to obtain a second secret key; Inputting the second secret key into the improved cross-hybrid coupling mapping lattice chaotic system to obtain a third chaotic sequence; The second split image is subjected to odd-even splitting scrambling and bidirectional diffusion based on the third chaotic sequence to obtain a second encrypted image.

8. The image encryption algorithm for preventing ciphertext tampering attacks according to claim 1 is characterized in that: Constructing a final encrypted image based on the first encrypted image and the second encrypted image specifically includes: The first encrypted image and the second encrypted image are subjected to bit plane separation and combination to obtain a final encrypted image.

Images