To enhance the embedding capacity and security of reversible data hiding in encrypted images (RDHEI), an RDHEI algorithm based on variational lossless compression (VLC) and dual encryption is proposed. Firstly, VLC model is introduced to ensure reversibility while achieving high embedding capacity. On the basis of variational autoencoder model, the VLC model incorporates an error encoding module to record the difference between the input and output images, thereby achieving lossless compression. Subsequently, dual encryption includes both stream encryption and model encryption, ensuring security both in the carrier and method, and original images necessitate dual decryption for accurate recovery. Experimental results demonstrate that the proposed algorithm elevates embedding rate by at least 0.12 bpp in UCID compared to existing algorithms, and can resist brute force attacks to achieve high security.

Reversible data hiding in encrypted images (RDHEI) has been recognized as an effective method for overcoming management difficulties within picture archiving and communication system (PACS). However, most existing RDHEI algorithms still encounter notable challenges when applied to the PACS, specifically in terms of their key management, embedding capacity, and security. This paper introduces a novel framework and corresponding algorithm for reversible data hiding in encrypted medical images (RDHEMI) to bridge this gap. The framework employs a unique key for each patient and maintains consistency in the key linked to patient images regardless of changes in doctor, thereby addressing key management challenges. In the proposed algorithm, Huffman tree coding (HTC) integrates Huffman coding with innovative leaf-to-leaf coding, achieving a better compression performance for medical images than move-to-front (MTF) cache and Huffman coding, as medical images contain more smooth areas. Count-encryption (CE) produces encryption keys according to the frequency of encryption occurrences for an image and ensures a peak signal-to-noise ratio under 8 dB for multiple encryptions with the same key, enhancing the algorithm’s resistance to attacks. The experimental results demonstrate that the proposed algorithm achieves high security to counter various attacks and outperforms existing algorithms in terms of the time complexity and embedding capacity, with an improvement of 0.21 bpp.

For the security risks and high transmission/storage consumption in cloud-based medical images storage systems (CMISS), reversible data hiding in encrypted images (RDHEI) provide an effective solution. Nevertheless, challenges persist concerning the security risks cause by key transmission and the large file size of encrypted medical images. Consequently, a cloud-based privacy-preserving medical images storage scheme with low consumption is proposed in this paper. First, RDHEI is applied to CMISS, where image encryption achieves privacy protection, reversible data hiding eliminates extra space consumption by index data self-hiding, and the reversibility enables lossless recovery and extraction of medical images and index data. Then, hybrid encryption is designed to achieve high security. The security of encrypted images is guaranteed by combining a one-time cryptosystem with symmetric XOR encryption, which makes our scheme can resist various attacks. Time-varying key used in XOR is encrypted by asymmetric RSA, and only public key is used in RSA, avoiding the risk of private key transmission. Finally, to reduce the file size of encrypted images and achieve low consumption, context Huffman coding is proposed to adaptively selects the block coding method by context and thresholds, and has at most 98 056 bits shorter than Huffman coding in encoded stream length. Experimental results show that the proposed scheme has better performance in terms on security, consumption, and reversibility. The minimum compression ratio in databases is 32.46%, which is 2.63% lower than the existing schemes. And the medical image and index data can be restored lossless.

Existing JPEG encryption approaches pose a security risk due to the difficulty in changing all block-feature values while considering format compatibility and file size expansion. To address these concerns, this paper introduces a novel JPEG image encryption scheme. First, the security of sketch information against chosen-plaintext attacks is improved by increasing the change rate of block-feature values. Second, a classification global permutation approach is designed to encrypt the undivided run/size, value (RSV)-based AC groups to achieve larger changes in the block-feature values. Third, to reduce file size expansion while maintaining format compatibility, the DC coefficients are rotated based on the mapped DC differences in the same category, and the nonzero AC coefficients are mapped in the same category. Extensive experiments demonstrate that the proposed algorithm is superior to existing schemes in terms of security. Notably, the average change rate of block-feature values is increased by at least 20%. Furthermore, the proposed scheme reduces the file size by an average of 2.036% compared to existing JPEG image encryption methods.

In the existing JPEG image encryption schemes , the block feature values that can be used to reduce key search space are either difficult to be changed or need to be changed through overflow processing which leads to low generality and high encryption runtime. To change block feature values without overflow processing, a novel JPEG image encryption scheme is proposed. For AC encryption, the complete and end AC groups based on undivided RSV (run/size, value) (ACG-URSV) are permuted separately to change different features. Complete ACG-URSV containing different number of RSVs is used to change the non-zero coefficients count (NCC) and energy of AC coefficients (EAC). End ACG-URSV containing the zero coefficients after position of last non-zero AC coefficient (PLZ) is mainly used to change PLZ. Besides, the intra-block RSV permutation and block permutation are used to further destroy correlation. For DC encryption, the positive DC prediction error (PDC-PE) groups modulo encryption is proposed to avoid overflow processing. The experimental results show that this paper reduces encryption runtime by more than half, improves generality by at least 20%. When quality factor of 90, the average change rates of NCC, EAC and PLZ values are increased by 96.28%, 11.68% and 29.15%, respectively.

Reversible data hiding in encrypted images (RDHEI) technique can be used to realize privacy protection and management in the image outsourcing scenario. Most existing RDHEI schemes focus on increasing the maximum embedding rate (Max-ER), but not paying much attention to the security improvement under various attacks. In this paper, a RDHEI method based on the adaptive bit-plane (ABP) coding is proposed to improve the Max-ER. The order-index extended scrambling (OIES) encryption scheme is also developed to strengthen the RDHEI's ability of thwarting various attacks. The effectiveness of ABP coding is achieved by proper selections of the threshold. The OIES enables the design of a novel scramble-key (SK) generation method to greatly reduce the probability of generating the same SK by the same user-key. This significantly improves the ability of resisting various attacks in that the attack on the scrambling encryption is mainly via the SK rather than the user-key estimation. Analysis shows that the probability of OIES obtaining the same SK is reduced from 1.0 to 0.01 for different images and to 1/2αfor the same image. Simulation results demonstrate that the proposed ABP coding and OIES schemes outperform the state-of-the-art RDHEI algorithms in terms of the Max-ER and ability against various attacks.

Image privacy protection and management face many challenges, such as privacy disclosure, copyright dispute, and traceability difficulties, with the development of big data. Reversible data hiding in encrypted images (RDHEI) has been widely considered as an effective means to tackle these challenges. In this paper, a RDHEI based on time-varying Huffman coding table (TV-HCT) method is proposed to improve the security, embedding rate (ER) and efficiency. First, the initial HCT is generated according to the prediction errors of an image, which can improve compression performance. And then, the TV-HCT is obtained by scrambling equal-length codewords in the initial HCT using timestamps. This realizes the time variability of compression coding stream (CCS) of an image in that the image TV-HCT has large change space. Analysis shows that the average change space of TV-HCT in UCID is 3.97×10327, and the average ER of three databases is more than 0.44 bpp higher than the existing algorithms. Finally, the CCS is encrypted using the designed index class scrambling method to balance complexity and security. The proposed method not only strengthens the security against brute force attack and differential attack, but also improves ER and efficiency of the RDHEI technique. Experimental results and performance analysis demonstrate that the proposed algorithm outperforms the state-of-the-art RDHEI algorithms in terms of the security, ER and complexity.