To achieve high tampering localization precision and low distortion, a semi-fragile reversible watermarking for authenticating 2D engineering graphics is proposed based on an improved region nesting and a novel watermark generation. First, an intensive investigation is performed to the recently proposed region nesting (RN) partition. It is found that the original vertex and its mapped one cannot be guaranteed to be on the same line, which means that it still has room for improvement in term of distortion. Based on this, an improved region nesting partition (IRN) is proposed. Secondly, inspiring by the idea of soldiers parading, a novel watermark generation based on the short hash of the adjacent geometric features is developed. Then, a new coordinate system is constructed to achieve invariability of translation, scaling, rotation and entity re-arrangement. Based on the above techniques, a semi-fragile reversible watermarking for authenticating 2D engineering graphics is put forward. Experimental results and analysis show that IRN can obtain at least 15% distortion reduction compared with RN, the precision of tampering localization can be improved to a single vertex, and a certain semi-fragility in translation, scaling, rotation, and entity re-arrangement can be achieved. Furthermore, it has no file size expansion, and can obtain a good balance among imperceptibility, semi-fragility and tampering localization precision.

To accomplish robust watermark extraction in reversible watermarking both in plaintext domain and encrypted domain, a separable robust reversible watermarking in encrypted 2D vector graphics is proposed in this paper. Firstly, a content owner uses a key to scramble the polar angles of the vertices to encrypt the graphics in the polar coordinate system. Consequently, a watermark embedder maps the encoded watermark segments to different vertices under the control of an embedding key and an HMAC (hash-based message authentication code) function. After that, the polar angle of the vertex is slightly adjusted to embed a watermark. Since the decryption operation does not affect the embedded watermark, the watermark can be extracted both in the plaintext and encrypted domain. Experimental results and analysis show that the proposed scheme can achieve good invisibility and reversibility. It can effectively resist normal operations such as rotation, scaling, translation (RST) and entity reordering, and it has good robustness against malicious attacks such as vertices/entities addition, deletion and modification.

Designing selective encryption (SE) schemes for H.265/HEVC has been attracted much attention with the advent of H.265/HEVC codec in the past two decades. However, the most SE algorithms for H.265/HEVC encrypt the syntax elements in the bypass mode to keep the bit rate. Moreover, the edge region of the video data is not sufficiently protected. To produce large visual distortion and edge loss, a tunable SE scheme for H.265/HEVC based on the chroma intra prediction mode (IPM) and coefficient scrambling is proposed. First, a pseudo-random number sequence is generated by AES-CTR. Then, the prediction, residual, and reconstruction information in the H.265/HEVC encoding process is encrypted by a pseudo-random sequence. It encrypts the syntax elements of context-based adaptive binary arithmetic coding (CABAC) in the bypass mode. Some syntax elements, including chroma IPM in the regular mode, are encrypted as well. To further protect the edge information, a coefficient scrambling is adopted. The edge information of each frame is extracted and the transform units (TUs) are classified according to it. Then, the coefficients of the TUs containing edge are scrambled. Finally, a sign used for marking the type of each TU is embedded into a coefficient. The experimental results and analysis show that the proposed scheme has better visual distortion and subjective evaluation results compared with some existing H.265/HEVC SE algorithms. Meanwhile, users can flexibly use the proposed SE scheme according to encryption performance and bit rate requirements, which is attractive in the scenario of protecting video in cloud servers.

Currently, much attention has been paid to reversible data hiding (RDH) in an encrypted domain due to the popular deployment of cloud storage. However, nearly all existing RDH schemes in the encrypted domain are proposed for raster images, and very little work has been done to 2D vector graphics, which are represented in real numbers. In this paper, a reversible mapping model for real numbers is first built. It maps the points in Rnto 2snon-intersecting subsets in Rn, which guarantees that s bits can be embedded into each real number. Based on the model, an RDH scheme in encrypted 2D vector graphics is put forward. In the scheme, a user encrypts 2D engineering graphics and stores them in the cloud, and then the cloud service provider can perform information hiding, extraction, and even recover the encrypted 2D vector graphics. For the authorized user, it can acquire the recovered 2D vector graphics from the cloud and obtain their original versions after decryption. For an unauthorized user, he can only acquire the encrypted 2D vector graphics with a hidden message, and only approximate 2D vector graphics can be obtained even if he knows the decryption key but does not know the hiding key. The experimental results and analysis show that it can strike a good balance between security, distortion, and capacity. It provides a new paradigm for RDH in the encrypted domain for the data represented in real numbers.

With the aim of reducing the distortion of traditional partitions, this paper investigates a novel method that partitions every square region into 2nnesting sub-regions. Based on the partition, a low-distortion reversible watermarking for 2D engineering graphics is proposed. The watermark is embedded by mapping the vertices in the original region to its corresponding sub-regions, and it is extracted according to the locations of the mapped vertices. Meanwhile, the original locations of the vertices can be restored by inverse mapping. Furthermore, by constructing a new coordinate system, the rotation, scaling, and translation semi-fragility of the watermarking can be achieved. Experimental results and analysis show that the proposed watermarking achieves good performance in terms of the capacity and semi-fragility, while the imperceptibility of the watermarking is significantly improved in comparison with the existing algorithms under the same conditions.