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In this paper, we proposed a novel reversible data hiding method in encrypted image (RDHEI), which is based on the compression of pixel differences. In the proposed method, at the content owner’ side the image is divided into non-overlapping blocks, and a block-level image encryption scheme is used to generate the encrypted image, which partially retains spatial correlation in the blocks. Due to the spatial correlation, in each block the pixels are highly likely to be similar. Therefore, the pixel differences in all blocks are concentrated in a small range and can be compressed. By the compression of pixel differences, the data hider can vacate the room to accommodate secret data in the encrypted image without losing information. At the receiver’s side, the receiver can obtain secret data or retrieve the original image using different keys with no error. The experimental results demonstrate that, compared with existing methods, the proposed method can achieve a higher capacity and visual quality.

The phenomenal advances of cloud computing technology have given rise to the research area of privacy-preserving signal processing, which aims to preserve information privacy even when the signals are processed in an insecure environment. Privacy-preserving information hiding is a multidisciplinary study that has opened up a great deal of intriguing real-life applications, such as data exfiltration prevention, data origin authentication, and electronic data management. Information hiding is a practice of embedding intended messages into carrier signals through imperceptible alterations. In view of some content-sensitive scenarios, however, the ability to preserve perfect copies of signals is of crucial importance, for instance, considering the inadequate robustness of recent artificial intelligence-aided automated systems against noise perturbations. Reversibility of information hiding systems is a valuable property that permits recovery of original carrier signals if desired. In this paper, we propose a novel privacy-preserving reversible information hiding scheme inspired by the mathematical concept of quadratic residues. A quadratic residue has four (not necessarily distinct) square roots, which enables payloads to be encoded in a dynamic fashion. Furthermore, a predictive model based upon the projection theorem is devised to assist carrier signal recovery. The experimental results showed significant improvements over the state-of-the-art methods with regard to capacity, fidelity, and reversibility.

In this paper, a novel, real-time, error-free, reversible data hiding method for encrypted images has been proposed. Based on the (7, 4) Hamming code, we designed an efficient encoding scheme to embed secret data into the least significant bits (LSBs) of the encrypted image. For reversibility, we designed a most significant bit (MSB) prediction scheme that can recover a portion of the modified MSBs after the image is decrypted. These MSBs can be modified to accommodate the additional information that is used to recover the LSBs. After embedding the data, the original image can be recovered with no error and the secret data can be extracted from both the encrypted image and the decrypted image. The experimental results proved that compared with existing methods, the proposed method can achieve higher embedding rate, better quality of the marked image and less execution time of data embedding. Therefore, the proposed method is suitable for real-time applications in the cloud.

Recently, the development of phase change memory (PCM) motivates new hybrid memory architectures that consist of PCM and DRAM. An important issue in such hybrid memory architectures is how to manage the pages resisting in heterogeneous memories. For example, when a requested page is missing in the hybrid memory and the memory has no free spaces, what pages in which type of memory (PCM or DRAM) should be replaced? This problem is much different from traditional buffer replacement management, where they do not consider the special properties of different types of memories. In particular, differing from DRAM, PCM is non-volatile but it has lower access speeds than DRAM. Further, PCM has a limited write endurance which implies that it cannot be written endlessly. Therefore, we have to design a new page replacement algorithm that can not only maintain a high hit ratio as traditional algorithms do but also can avoid frequent writes to PCM. In this paper, aiming to provide a new solution to the page replacement problem in PCM/DRAM-based hybrid memories, we propose a new algorithm called MHR-LRU (Maintain-hit-ratio LRU). The objective of our algorithm is to reduce PCM writes while maintaining a high hit ratio. Specially, it keeps recently updated pages in DRAM and performs page migrations between PCM and DRAM. The migrations take into account both page access patterns and the influences of page faults. We conduct trace-driven experiments and compared our proposal with some existing algorithms including LRU, LRU-WPAM, and CLOCK-DWF. The results show that our proposal is able to efficiently reduce PCM writes without degrading the hit ratio. Thus, our study offers a better solution for the page replacement issue in PCM/DRAM-based hybrid memory systems than previous approaches.