The Research On 2D Engineering Graphics Encryption Technology Based On Transform Domain

With the development of the Internet techniques, communication privacy and information security are attracting a lot of attention recently. But the research on the cryptograph for two-dimensional engineering graphics is rare, and most of research encrypt the format of graphics, not encrypt the contents of them.This paper makes a deep investigation into the encryption techniques of 2D engineering graphics'contents based on chaos scrambling and transform theory. The background, feature, classification and current research status of 2D engineering graphics encryption are first presented, followed by analyzing the shortcomings in the existing encryption algorithms. And then, the relevant theoretical knowledge, including Chaos Theory, Fourier Transform and Discrete Cosine Transform, and their respective features are introduced. Finally, two encryption schemes which encrypt the contents of the 2D engineering graphics are proposed, based on the current research status of the 2D engineering graphics encryption.A multiple encryption algorithm is first proposed for 2D engineering graphics based on Fourier Descriptors and chaos scrambling for 2D engineering graphics. The specific coordinates of vertices in the 2D engineering graphics are extracted to construct the corresponded complex signals, which are in turn transformed by Fourier transformation, then bit XOR operation is used between the FFT magnitude coefficients and a binary sequence, which is generated from chaotic system. At last, chaos scrambling (translation, rotation, zooming) is done to the entities of the 2D engineering graphics. That is the encryption of the content of the 2D engineering graphics. The other encryption algorithm is an encryption algorithm of variable strength based on a Cosine Descriptor and the coupled chaos for 2D engineering graphics. The specific coordinates of vertices in the 2D engineering graphics are extracted to construct the corresponded complex signals, which are in turn transformed by Discrete Cosine transformation group by group, then bit XOR operation is used between the selective AC magnitude coefficients and a binary sequence, which is generated from a key. That is the variable strength of encryption of the content of the 2D engineering graphics. Simulation and analysis results show that the key space is large, and the algorithms are sensitive to the key, which guarantee the security of 2D engineering graphics. The encryption approaches proposed in this thesis encrypt the contents of the 2D engineering graphics to ensure their safety, and can thus be used for encryption protection of 2D engineering graphics.