Software Watermarking Technology

As network technology makes software products spread widely and faster, problems have arisen sharply in protecting intellectual property rights. In the beginning software was protected by encryption technology through hiding information content. However, with the further research of encryption algorithms and the development of computer hardware technology , encrypting software does not worked well in protecting software copyrights and is hard to prove the copyrights in the case of piracy. In such circumstance, software watermarking technique is created for the purpose of protecting information by hiding its presence.As a significant branch of digital watermarking, software watermarking is still in the elementary level theoretically. The threats faced by software products come mainly from such three aspects as software piracy, reverse engineering and malicious tampering. Software can be protected as against its three threats in the following three ways, i. e. software watermarking, software obfuscation and software tamper-proofing. As a technical means to guard against copyright piracy, software watermarking technique can make copyright protection and user ID information hidden in the software and by the hidden information prove the copyright owners and trace down the copyright pirates. As a technical means to guard against reverse engineering, software obfuscation makes it harder to do so by implanting semantics preserving into program lexical, data structure or control flow. Besides this the owners can employ the same method to embed watermarks and also the pirates can employ it to destroy the watermarks so as to realize their piracy. As a technical means of preventing malicious tampering, software tamper-proofing makes it harder to tamper with software by real-time tracing the tampering and terminating the running of the program.The chief task of software watermarks is to perfect the theory of watermarking and devise more reliable watermarking algorithms. Its long-term aim is to set up an evaluation system for software watermarking scheme, bring software protectionmeasures into development plan and formulate engineering standard and put theoretical research of watermarking technique into practical application as a powerful tool for intellectual property protection in software industry.A few recent years many algorithms of software watermarks are presented, and dynamic graph based software watermarking is one of the more typical. This thesis has done some researchs on dynamic graph based software watermarks . First, the writer devises a software watermarking scheme of binary tree based radix encoding, in which constants existed in watermarking data are encoded according to inner structure and the tampering can be found immediately when the watermark has been tampered with and then the program shall be terminated to run. Second, the writer presents a robust watermarking scheme based on concurrently controlled multithread, in which a redundant dynamic watermarking graph is embedded and the watermarking graph can be extracted reliably when tampered with.Third, the writer proposes a scheme of preferring to split watermarking data rather than watermarking graph in order to disperse watermarking codes. The scheme is based on splitting and retrieving watermarking data through Chinese Remaindering Theorem and by embedding dynamic graph and extracting watermarking codes to enhance the stealth and the data rate. One characteristic of the scheme is that watermarking data can break through the limitation of the word length and the inconnection dilemma between watermark sub-graphs. Besides the above three aspects, the paper further presents a novel scheme of software watermarks based on neural network, in which the watermark is embedded in the execution trace of the program and is formed a pattern through the study of neural network ,when a copyright dispute arises, the neural network can check the existence of the watermark by its pattern recognition function instead of extracting it exactly,so the scheme shows something of robustness.