Research On Reversible Watermarking Of2-Dimensional Vector Graphics For Content Authentication

With the development of computer-aided design (CAD), computer-aided manufacturing (CAM) and geographic planning and design,2D vector graphics have been widely used in the field of construction, machinery and geographic information industry because of its advantages of high accuracy, scaling without distortion and easy storage. However, due to the vulnerability of networks, illegal tampering, secret disclosure, copyright infringement are becoming outstanding problems of them. Recently, the security and integrity protection of2D vector graphics have been paid much attention. Although traditional encryption methods can protect the content of them during transmission, the protection will be failed after their decryption. As an complement method other than the traditional encryption methods, another technology named as digital watermarking is proposed to protect the copyright, source authentication or integrity of the data in open network environment.This thesis first introduced the history and the state-of-the-art of digital watermarking technology, and then systematically elaborated the theory of digital watermarking, including the principle of digital watermarking, the implementation process of embedding and extracting, watermark classification and performance evaluation, etc. Then, the data characteristics of two-dimensional vector graphics have been analyzed in detail, and the research status of reversible watermarking and integrity authentication watermark of vector graphics is summarized. Based on the existed research on theory and technology, this paper is mainly focused on the reversible authentication algorithm with tampering localization ability for vector graphics, the main works of the paper are as follow:1. Considering the high correlation between the adjacent vertex coordinates of two-dimensional vector map, an improved reversible contrast mapping algorithm for vector maps is proposed. The reversible watermark method can completely restore the original data, which has good reversibility and invisibility.2. A semi-fragile reversible watermarking algorithm based on improved difference expansion is proposed in the polar mapping system, and the watermarking operation is done in the feature points of each entity. Experimental results show that the algorithm not only can achieve good invisibility, reversibility, but also has the good watermark capacity and ability to resist geometric attacks, and can precisely locate the attacks such as entity addition, deletion and modification. It can verify the integrity of two-dimensional vector graphics.3. A watermarking authentication system for two-dimensional vector graphics is designed and implemented. It verifies and validates the effectiveness of the two algorithms proposed in this thesis.The two reversible watermarking algorithms proposed above not only can restore the original vector graphics, and verify the integrity of the watermarked vector graphics, but also can accurately locate the tampered area. It well suited for the applications with high data accuracy.