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I. Introduction
With the arrival of the information age, especially the popularity of the Internet, the problem of security protection of information is increasingly prominent. The current information security technology is basically based on cryptographic theory. Whether it is using a traditional key system or a public key system, its protection mode is the access to the control file, which is to encrypt the file into a secret, so that illegal users cannot Interpretation. However, with the rapid improvement of computer processing capabilities, this method of increasing system levels by increasing the key length is getting more unsafe.
On the other hand, multimedia technology has been widely used, and there is more and more acoustic image data that requires encryption, authentication and copyright protection. Digital sound image data is essentially a digital signal. If you use a password encryption method for such data, its own signal attribute is ignored. In recent years, many researchers have abandoned traditional password technology routes, and attempts to hide the sound image data with various signal processing methods, and use the technology to make multimedia's "digital watermark".
Second, the number of sketches - Digital Watermark technology refers to an embedded marker in digital multimedia data, which is usually invisible, only by passing A dedicated detector or reader can be extracted. Digital watermarks are an important research direction of information hiding technology. The information in embedded digital works must have the following basic characteristics to be called digital watermarking:
Concealation: Embedding digital watermarks in digital works will not cause significant degradation and not being perceived. Hidden location security: Watermark information is hidden in data instead of the file header, the transformation of the file format should not cause loss of watermark data. Robust: The so-called robustness refers to that digital watermarks can remain complete or can still be accurately identified after a number of unintentional or intentional signal processing processes. Possible signal processing includes channel noise, filtering, number / mode / digital conversion, sequential, shear, displacement, scale change, and lossless compression coding. In digital watermarking technology, the amount of watermarks and robustness of the watermark constitute a basic contradiction. From subjective, the ideal watermark algorithm should be hidden in large amounts of data, but also resist various channel noise and signal deformation. In practice, however, these two indicators often do not implement simultaneously, but this does not affect the application of digital watermarking technology, as practical applications generally only emphasize one of them. If it is for hidden communication, the amount of data is obviously the most important. Because the communication mode is extremely concealed, the possibility of enemy tampering attack is small, so it is not high. However, for the guarantee data security, the situation is exactly the opposite, and the various confidential data is facing the risk of being stolen and tampered, so robustness is important. At this time, the requirements of hidden data are secondary.
The basic ideology of digital watermarking technologies originated from ancient neckout. The ancient Greece's Spartan once combined military information on ordinary wooden boards, filled with paraffin, and only used fires to grilled hot wooden boards. After melting paraffin, they can see secrets. I am afraid that the use of the widest way to write, milk, white, juice, etc. have served as a role of crypto water. It can be said that most of the patient's early use of the confidential communication means is a text instead of a password. However, compared with the cryptography technology, the method has never developed into an independent discipline, the reason is mainly because of the lack of necessary theoretical foundation.
Today, the development of digital technology is injecting new vitality into ancient neckout, and it has brought new opportunities. During the study of digital watermarking, the researchers have borrowed the idea of writing technology. Especially in recent years, the development of information hidden technology theory framework research has brought hope to a rigorous science. There is no doubt that the method will be revived in the digital era.
Third, Digital Watermarking Classification Digital Watermark Technology can be divided from different angles. 1. Divide by characteristics
According to the characteristics of the watermark, digital watermark can be divided into two categories of robust digital watermarks and fragile digital watermarks. Robust Digital Watermark is mainly used to identify copyright information in digital works, such as author, work number, etc., which require embedded watermarks to withstand various common editing processing; fragile digital watermarks are mainly used for integrity protection, with robust watermarks In contrast, fragile watermarks must be sensitive to signal changes, and people can determine whether the data is tampered with according to the state of fragile watermark. 2. Media division by watermark
According to the media attached to the watermark, we can divide digital watermarks into image watermark, audio watermark, video watermark, text watermark, and grid watermark for three-dimensional grid model. With the development of digital technology, there will be more types of digital media that will also generate corresponding watermarking technologies.
3. Division according to the test process
According to the detection process of the watermark, the digital watermark can be divided into clear text-printing and blind watermarks. Ming Text Watermark requires raw data during the detection process, and the detection of blind watermarks only requires a key and does not require raw data. In general, the robustness of the plaintest watermark is relatively strong, but its application is limited by the storage cost. Most of the digital watermarks currently in the academic circulation are blind watermarks.
4. Divide
The content of the digital watermark can be divided into meaningful watermark and unconscious watermark. The meaningful watermark means that the watermark itself is also a digital image (such as a trademark image) or a digital audio fragment; meaningless watermark only corresponds to a serial number. The advantage of meaningful watermark is that if the decoded watermark is damaged due to attack or other reasons, people can still confirm whether there is watermark by visual observation. However, for the meaningless watermark, if the decoded watermark sequence has several symbol errors, it is only possible to determine whether the signal contains watermarks in the signal.
5. Divide by use
Different application needs have made different watermark techniques. According to the use of watermark, we can divide the digital watermark into a ticket anti-counterfeiting watermark, copyright protection watermark, tampering suggests watermark and hidden identification watermark.
The banned anti-counterfeiting watermark is a relatively special watermark, mainly for printing tickets and electronic bills. In general, the manufacturer of counterfeit coins cannot be modified to the ticket image, so signal editing operations such as scale transform are not considered. On the other hand, people must consider whether the bill is damaged, the pattern blur, and considering the requirements of rapid detection, the digital watermarking algorithm for the ticket is not too complicated.
Copyright Identification Watermark is the current topic of digital watermarks. Digital works are both goods and intellectual works. This double weight determines the copyright identification watermark mainly emphasizes concealedness and robustness, and the requirements for data are relatively small.
Tamper suggests watermarking is a fragile watermark, its purpose is to identify the integrity and authenticity of the host signal.
The purpose of hidden identification watermark is to hide the important label of confidential data to limit illegal users to confidential data.
66. Positioned by watermark hidden location
According to the hidden position of the digital watermark, we can divide it into time (empty) domain digital watermark, frequency domain digital watermark, time / frequency domain digital watermark and time / scale domain digital watermark.
When the digital watermark is overlapping watermark information directly on the signal space, and the frequency domain digital watermark, the time / frequency domain digital watermark and time / scale domain digital watermarks are in the DCT transform domain, time / frequency transform Hide watermarks on the domain and wavelet transform fields.
With the development of digital watermarking technology, the various watermark algorithms are endless, and the hidden position of the watermark is no longer limited to the above four. It should be said that as long as a signal transformation is constituted, it is possible to hide water in its transform space.
IV. Application prospects The rapid development of multimedia technology and the popularity of the Internet have brought a series of political, economic, military and cultural issues. There have been many new research hotspots. The following few issues have made a universal concern to form a digital watermark. Research Background. 1. Intellectual property protection of digital works
Digital works (such as computer art, scanned images, digital music, video, 3D animation) copyright protection is current hot problems. Due to the copy of the digital works, the modification is very easy, and it can be exactly the same as the original work, so the original person has to use some of the serious damage to the quality of the work to add the copyright mark, and this obvious visible sign is easily tampered. "Digital Watermark" uses data hidden principles to make copyright markers can not be visible or not listening, neither damage the original work and reach copyrighted purpose. At present, digital watermark technology for copyright protection has entered the preliminary practical phase, and IBM provides digital watermarking features in its "Digital Library" software, and Adobe has also integrated Digimarc companies in its famous Photoshop software. Digital watermark plugin. However, seeking truth from facts, however, digital watermark products on the market are still immature, it is easy to be destroyed or cracked, and there is still a long way to go in real practical use.
2. Bills in business transactions
With the development of high-quality image input and output equipment, especially the color inkjet, laser printers and high-precision color copiers, which makes currency, check, and other bills of fake make it easier.
According to US official report, only a small-scale counterfeit bank made of a high-precision color printer in 1997 is 19%, which is 9.05 times in 1995. Currently, both the United States, Japan, and the Netherlands have begun to study digital watermarking technologies for ticket security. The Media Laboratory of MIT is entrusted by the US Treasury, and has begun to add unique, invisible digital watermarks in each image of the color printer. There is no, quickly identify authenticity.
On the other hand, in the process of transformation from traditional business to e-commerce, there will be a large excessive electronic document, such as scanning images of various paper notes. Even after the network security technology matures, various electronic bills also need some non-passing authentication methods. Digital Watermarking technology can provide invisible certification marks for a variety of bills, which greatly increases forged difficulty.
3. Hidden identity and tampering prompt of sound image data
The identification information of the data is often more confidential than the data itself, such as the shooting date of the remote sensing image, / latitude, etc. Data without identifying information is sometimes even unused, but these important information tagged directly on the original file and dangerous. Digital Watermarking technology provides a hidden identity, identification information is not seen on the original file, only through a special reading program. This method has been adopted by some publicly available remote sensing image databases.
In addition, tampering prompts are also a very important job. Existing signal stitching and mosaic technology can be "shifting flowers" rather than known, so how to prevent tampering attacks on images, recording, video data is an important research topic. Digital watermark-based tamper is an ideal technical way to solve this problem, and by hiding the watermark state, it can be judged whether the sound image signal is tampered with.
4. Concealed communication and its confrontation
The information hidden technology depends on digital watermark not only provides non-password safety channels, but also triggered the revolution of information warfare, especially the network intelligence war, producing a series of new operations, causing attention to many countries.
Network Intelligence War is an important part of the information war, and its core content is to use public networks to confidential data transfer. So far, the research ideas in this area have not been able to break through the "document encryption" thinking. However, encrypted documents are often unordered, and it is easy to pay attention to attackers. The widespread application of network multimedia technology makes a new idea using public networks, using digital sound image signals with respect to human visual, auditual redundancy, can carry out various time (empty) domains and transform domain information hidden, Thereby hidden communications.
V. Research Dynamics From the public published literature, the international research on digital watermarks has just begun, but due to the involvement of large companies and the support of the US military and the Ministry of Finance, the development speed of this technology is very fast. . Since 1998, many international journals such as "IEEE Image Handling", "IEEE Meeting", "IEEE Communication Selection", "IEEE Consumer Electronics" have organized digital watermarking technology special issues or special news reports. In the United States, a batch of research institutions and enterprises represented by the Massachusetts Institute of Technology have applied for patents for digital watermarking. In 1998, an AD report on image data hidden appeared in the US government report. At present, agency that has supported or carried out digital watermark research has both government departments, universities and well-known companies, including US Treasury, US Copyright Working Group, US Air Force Research Institute, US Army Research Lab, German National Information Technology Research Center , Japan NTT Information and Communication System Research Center, Massachusetts Institute of Technology, Illinois University, Minnesota University, Cambridge University, Swiss Lausanne Federal Institute of Technology, Spain Vigo University, IBM Watson Research Center, Microsoft Cambridge Research Institute, Lucent Company Bell Lab, CA Company, Sony, NEC Research Institute and the Netherlands Philips, etc. From May 30th to June 1, 1996, the first international information hidden academic seminar was held in the British Newton Institute of Jinchang, and has been held in the third year. Some important international conferences in SPIE and IEEE have also opened the relevant topics.
my country's academic community's response to digital watermarking technology is very fast, and there is a relatively large number of research institutions to invest in this area. In order to promote the research and application of digital watermarks and other information hidden technology, in December 1999, Heorda Academician, my country's information security field, Zhou Zhongyi academician, Ji Ji people jointly launched my country's first information hidden academic seminar . In January 2000, the National Key Laboratory organized by the National "863" Intelligent Machine Expert Group and the Automation of Chinese Academy of Sciences held a digital watermark academic seminar, from the National Natural Science Foundation of China, National Information Security Evaluation Centers, Chinese Academy of Sciences, Beijing University of Posts and Telecommunications, National University of Defense Technology, Tsinghua University, Northern University of Technology, Shanghai Jiaotong University, Tianjin University, University of Science and Technology, Peking University, Beijing University of Science and Technology, Sun Yat-sen, Beijing Electronic Technology Application Research Institute and other units experts scholars and researchers The key technologies of digital watermarks were discussed in depth and reported their own research results. From this conference reaction, research in my country's related academic fields is far from the world, and there is a unique research idea.
At present, agency that has supported or carried out digital watermark research has both government departments, universities and well-known companies, including US Treasury, US Copyright Working Group, US Air Force Research Institute, US Army Research Lab, German National Information Technology Research Center, Japan NTT Information and Communication System Research Center, MIT, Illinois University, Minnesota University, Cambridge University, Swiss Lausanian Institute of Technology, Spain Vigo University, IBM Watson Research Center, Microsoft Cambridge Research Institute, Lucent Company Bell Lab, CA Company, Sony, NEC Research Institute and the Netherlands Philip Company, etc.
From May 30th to June 1, 1996, the first international information hidden academic seminar was held in the British Newton Institute of Jinchang, and has been held in the third year. Some important international conferences in SPIE and IEEE have also opened the relevant topics.
