CN-122001991-A - Sequentially exchangeable thumbnail encryption and information hiding method

Abstract

The invention discloses a sequentially exchangeable thumbnail encryption and information hiding method, which is characterized in that images are processed through layered encryption, a key visual layer is encrypted in an accurate TPE processing mode, and additional information is embedded in an information bearing layer by utilizing a homomorphism-based information hiding technology. In addition, the scheme of the invention allows flexible exchange of encryption and information embedding sequences, thereby remarkably improving the flexibility and applicability of the system. The encryption and decryption processes are efficiently performed in combination with the spatial correlation of the image and the pseudo-random number generator, and the quality of the decrypted image is ensured. Experimental results show that the scheme provided achieves good balance in privacy protection, visual availability and non-visual availability, has higher processing efficiency, can effectively embed additional information on the premise of not losing image quality, and has wide application prospects.

Inventors

• LI RUIPING
• ZHAO YIJING
• HAN SHASHA
• LI MING
• GUO JING
• YUAN ZIYIN
• MAO YIMENG
• ZHANG RUN
• WANG QIUJU
• XING YUN

Assignees

• 河南师范大学

Dates

Publication Date

20260508

Application Date

20251224

Claims (5)

1. 1. A sequentially exchangeable thumbnail encryption and information hiding method is characterized by comprising the steps of dividing a bit plane of each image channel into a key visual layer and an information bearing layer by adopting layered encryption and combining a homomorphism-based information hiding technology, dividing an image into a plurality of blocks with the thumbnail size of b x b in the image encryption process, precisely TPE (thermoplastic elastomer) the key visual layer in the blocks, wherein the key visual layer mainly aims at preserving the thumbnail visual quality of the image, the information bearing layer adopts random diffusion encryption, and additional information is embedded in the information bearing layer, the main aim of the information bearing layer is to ensure the hidden property and the safety of the information embedding, and simultaneously reduce the influence on the visual quality of the image to the greatest extent.
2. 2. The sequentially exchangeable thumbnail image encryption and information hiding method as claimed in claim 1, wherein the specific process of image encryption is that the color image is composed of a plurality of channels, each channel is processed separately, a single channel is first separated into a key visual layer, namely a high five bit plane, and an information bearing layer, namely a low three bit plane, and each pixel value of the image is assumed to be H (i), wherein i represents a pixel position, and the key visual layer H MSB (i) and the information bearing layer H LSB (i) of the pixel are separated; for the key visual layer, firstly dividing the key visual layer into a plurality of blocks with the size of B multiplied by B, and recording as { B 1 ,B 2 ,...,B s }, wherein s represents the total number of blocks, conducting random disturbance encryption on pixels in each block, generating a safe random number sequence in the disturbance process of each block for guaranteeing the randomness and safety of encryption, generating a pseudo random sequence by calculating the pixel mean value of the previous sub-block according to the initial value, generating a pseudo random sequence by combining a pseudo random number generator, discarding the first f elements in the sequence for enhancing the safety, avoiding potential regularity, mapping the generated pseudo random sequence to a [0,31] interval as a basis for disturbing each pixel value, regarding each image block as an integral unit, selecting a central pixel as a stirring rod, conducting random disturbance on other pixels, compensating the central pixel according to the pixel value of the current disturbance, guaranteeing the sum of the pixels in the block to be kept unchanged, conducting the random disturbance on the pixels during the image encryption, leading to the fact that the three low-level three encrypted visual layers are not zero due to the fact that the pixel value can be changed during the image encryption, in order to avoid the influence of the change on the merging process of the images, the key visual layer is preprocessed, the pixel value of the key visual layer is divided by 8 to obtain an integer matrix ranging from 0 to 31, then the matrix is encrypted, and finally the matrix is multiplied by 8 after being encrypted, so that the low three bits of the encrypted key visual layer are always 0 after being processed, and the situation that collision with an information bearing layer is avoided during merging is ensured.
3. 3. The sequentially exchangeable thumbnail encryption and information hiding method as claimed in claim 2, wherein the specific process of calculating the minimum value and the maximum value of the adjustable range of pixel values is: Assuming mi is the minimum value of the adjustable range for the pixel, the calculation is formula (1): where H (i) is the current value of the pixel and H (c) is the current value of the center pixel in the block; assuming mx is the maximum value of the adjustable range for the pixel, the calculation is formula (2): After the block stirring operation is finished, each thumbnail block in the key visual layer is further subjected to block built-in messy encryption, and the arrangement sequence of the thumbnail blocks is disturbed by randomly replacing pixels in the image blocks, so that the encryption complexity is remarkably increased, the safety and privacy protection of an encrypted image are improved, the stirring and replacement operation can be alternately performed for further enhancing the encryption effect, the process is called an encryption wheel, the whole encryption process can be performed by R wheels, and each wheel has a superposition effect on the encryption effect of the image, so that the attack resistance and privacy protection capability of the image are effectively improved; For the encryption operation of the information bearing layer, a random key matrix key_lsb (i) of the same size as the image is used, wherein the value of each element is between 0 and 7, and the lower three bits are randomly diffused for encryption, and the specific formula is as follows: Where k_lsb (i) is the encryption key generated for each pixel and H' LSB (i) is the pixel in the encrypted information-bearing layer.
4. 4. The sequentially exchangeable thumbnail encryption and information hiding method as claimed in claim 1, characterized in that the specific procedure of the information embedding is that in the encrypted image or original image, the image is divided into a plurality of e×e-sized blocks denoted { E 1 ,E 2 ,...,E s }, where s represents the total number of blocks, the pixels in each block will carry one bit of hidden information, assuming that the information to be embedded is a binary sequence { a 1 ,a 2 ,...,a s }, where a i represents the information bit embedded in the ith block, the value is 0 or 1, the data embedder performs the flipping operation on the pixels in the information bearing layer according to the information bit a i to be embedded by dividing the pixels in each block E i into two sets Q 0 and Q 1 by one data hiding key in order to embed the hidden information: if a i = 0, the information-bearing layers of the pixels in set Q 0 are inverted: if a i =1, the information-bearing layers of the pixels in set Q 1 are inverted: Wherein flip LSB3 (Q) represents the flipping of the information bearing layers in set Q.
5. 5. The sequentially exchangeable thumbnail encryption and information hiding method according to claim 1, wherein the specific procedures of image restoration and information extraction are: firstly, a user decrypts an image by using an image encryption key, for recovering a key visual layer, a receiver decrypts the image by using the same key as that used in encryption, the image is divided into a plurality of blocks with the size of b multiplied by b, inverse scrambling operation is carried out according to the encryption key, the pixel sequence in the image blocks is recovered, and then each block is subjected to inverse block stirring, through the process, the receiver can successfully recover the key visual layer, and for an information bearing layer, the receiver decrypts by using a random diffusion key, and recovers the original content containing additional information; In decrypting, if a block of pixels belongs to Q 1 and the embedded data bit is 1, or a block belongs to Q 0 and the embedded data bit is 0, the decrypted information-bearing layer will differ from the original information-bearing layer in that the exclusive or operation will change the least three bits in these cases, resulting in an error between the encrypted image and the original image, in which case the sum of the errors between the decrypted information-bearing layer and the original information-bearing layer is 7, the average energy of the error being calculated by the formula: Wherein u represents a possible value of 0-7 of a three-bit binary number, and (7-u) represents a value of a corresponding original information bearing layer, and the difference between the decrypted value and the original information bearing layer is calculated; Since the probability of incorrect information bearing layer decryption is 1/2, when reconstructing an image using the decrypted data, the value of PSNR in the decrypted image is approximately: Then, the receiver uses the information extraction key, extracts hidden additional information according to the spatial correlation of the image, recovers the hidden information by analyzing the fluctuation condition of the decrypted pixel blocks, divides the pixels of each image block into two sets, namely Q 0 and Q 1 , respectively turns over the information bearing layers of the two sets to generate two candidate image blocks, and then can judge which block is closer to the original image by calculating and comparing the fluctuation values of the two candidate blocks, thereby correctly extracting the hidden information; turning the information-bearing layer in Q 0 , the operation generating a candidate recovery block indicating that the block is not interfered; turning the information-bearing layer in Q 1 , the operation generating another candidate recovery block, indicating that the block has been interfered with; the receiver judges which block is closer to the original block by calculating the fluctuation value of the candidate block, and the fluctuation value has the following calculation formula: where p (u, v) is the pixel value in the image block, by comparing the fluctuation values of the two candidate blocks, the receiver can select the block with better recovery quality: If the fluctuation value of the flipped block H 1 is higher, the original block is considered to be the block of flipped Q 0 , and the extracted information bit is 0; if the fluctuation value of the flipped block H 0 is lower, the original block is considered to be the block of flipped Q 1 , and the extracted information bit is 1; Finally, by processing each decrypted image block and combining the extracted additional information, the receiver can finally recover the complete original image, and all the extracted bits are spliced together to recover the complete hidden message.

Description

Sequentially exchangeable thumbnail encryption and information hiding method Technical Field The invention belongs to the technical field of image encryption and information hiding, and particularly relates to a sequentially exchangeable thumbnail encryption and information hiding method. Background With the widespread use of smart electronic devices, many users use smartphones and dedicated cameras to capture their daily lives. By 2025, humans would take about 2.1 trillion pictures. In contrast, 2024 taken 1.9 trillion photos (M.Broz,"How many pictures are there(2025):Statistics,trends,andforecasts,"https://photutorial.com/photos-statistics/,May2025). worldwide, because of the limited storage space of the local device, many images may cause additional pressure (P.PrajapatiandP.Shah,"AReview on Secure DataDeduplication:Cloud Storage Security Issue,"Journal ofKing Saud University-ComputerandInformation Sciences,vol.34,no.7,pp.3996–4007,2022). on the limited capacity of the device-limitations in local storage space-causing large numbers of users to rely on cloud storage services, but this also carries a serious risk of privacy leakage-spyware-permeable cloud account-stealing data (Torbet,Georgina."Pegasus Spyware Can Break into Users'CloudAccountsandStealData."DigitalTrends,21July2019), apple-iCloud photo scan plan-raised widespread concerns (Greenberg, andy. "APPLE WALKS A PRIVACY Tightrope to Spot Child abueini cloud." Wired,5 aug.2021). For this reason, the uk government has incorporated cloud services into national critical infrastructure to enhance security (DepartmentforScience,InnovationandTechnologyandTheRtHonPeter Kyle MP."Data Centres to Be Given Massive Boost and Protections from Cyber Criminals andITBlackouts."GOV.UK,12Sept.2024). Although the conventional image encryption technology (Y.Lin,Z.Xie,T.Chen,X.Cheng,andH.Wen,"Imageprivacy protection scheme based on high-quality reconstruction dct compression and nonlinear dynamics,"Expert Systems withApplications,vol.257,p.124891,2024;D.Singh and S.Kumar,"Image authentication and encryption algorithm based on rsa cryptosystem and chaoticmaps,"Expert SystemswithApplications,vol.274,p.126883,2025;Q.Lai,G.Hu,U.Erkan,andA.Toktas,"Anovelpixel-split image encryption schemebasedon2dsalomon map,"ExpertSystemswithApplications,vol.213,p.118845,2023) can effectively protect the privacy of the image, the visual effect of the image is generally seriously degraded, so that the image cannot be normally viewed and used under the condition of not being decrypted. The situation limits the wide popularization of the image encryption technology in practical application, and particularly, how to ensure privacy protection and also consider the usability of the image in the scene that the image needs to be stored in the cloud and quickly accessed becomes a difficult problem to be solved. The nature of the human visual system provides a potential basis for addressing image privacy and usability issues. Research has shown that human visual perception can rely on prior sensory data and knowledge to perform unconscious extrapolation, effectively identify images (Gregory R L.Knowledge in perception and illusion[J].Philosophical Transactions of the Royal Society of London.Series B:Biological Sciences,1997,352(1358):1121-1127). even at low resolution, and that personal familiarity with images can also improve accuracy of their identification (Kinjo H,Snodgrass J G.Does the generation effect occur for pictures?[J].The American journal ofpsychology,2000,113(1):95). so that low resolution thumbnails as blurred versions of common images can help improve usability while ensuring privacy. In this context, wright et al (Wright C V,Feng W,Liu F.Thumbnail-preserving encryption for JPEG[C]//Proceedings ofthe 3rd ACM workshop on information hiding and multimedia security.2015:141-146) propose an image encryption scheme based on a priori knowledge-Thumbnail preserving encryption (thumb-PRESERVING ENCRYPTION, TPE). The core idea of TPE is to keep thumbnail information while encrypting an image so that a user can quickly browse and recognize image content through thumbnail and a priori knowledge without revealing details of the image, thus balancing privacy protection with usability. In TPE schemes, the thumbnail after image encryption is either the same as the original image (ideal TPE)(Wright C V,Feng W,Liu F.Thumbnail-preserving encryption for JPEG[C]//Proceedings of the 3rd ACM workshop on information hiding and multimedia security.2015:141-146), or slightly changed (approximate TPE)(B.Marohn,C.V.Wright,W.-c.Feng,M.Rosulek,and R.B.Bobba,"Approximate thumbnail preserving encryption,"in Proceedings of the 2017on Multimedia Privacy and Security,2017,pp.33-43). However, most conventional TPE schemes ignore the non-visual usability of an image, and although they can preserve visual information of an image, they fail to effectively embed non-visual data, but users may also want to know some backgr