2003-04-28 13:12 Chen Yun Di / (chinabyte)
The wide application of computers and networks greatly facilitates people to get information and exchange information. Since digitized information is quickly and conveniently transmitted on a variety of forms, the government, enterprises and individuals gradually use the network as the main communication means, and a large number of important documents and personal information are stored and transmitted in digital form. E-commerce is used by our network. Various services are provided, and the network and information security issues are becoming more important.
The traditional information encryption method can encrypt the text information to ensure the security of its transmission, but if you want to encrypt the multimedia information such as the image, video, and sound, the cryptographic traditional encryption method is more difficult, with computer processing power Rapid improvement, this method of increasing system levels by increasing the length of the key is increasingly unreliable. In particular, with the development of network multimedia technology, information is not limited to text, many information is graphical image and video format, and there is more and more sound data that requires authentication and copyright protection. In addition, in the military field, people may need to hide a combat map in an artwork. These applications are the problem to be solved by digital watermarking technology.
Digital Watermarking Technology has developed a branch that hides in recent years. With the improvement of domestic information, the digital watermark technology will have a broader application prospect, this paper briefly introduces the concept of digital watermarking, the main application field and core technology. First, the concept and basic principles of digital watermark
Digital Watermark technology is directly embedded in multimedia content through a certain algorithm, but does not affect the value and use of the original content, and cannot be accused or noted by the person's perceptual system, only by dedicated Detector or reader can be extracted. The watermark information can be the author's serial number, company logo, a special text, etc., can be used to identify files, images, or music products, versions, original authors, owners, issuers, legal users to digital products The ownership. Unlike encryption technology, digital watermarking technology does not prevent pirated activities, but it can discriminate whether the object is protected, monitoring the propagation of the protected data, authenticity authentication, and illegal copies, and solving copyright disputes and provides evidence for the court.
Digital watermarks in embedded digital multimedia must have the following characteristics: invisible or concealedness is not easy to be perceived, and does not cause the original digital works to have a decline in image quality, that is, the existence of digital watermarks can not be seen.
Robustity is that the digital water print is not easily destroyed when the protected information has been changed, such as translation, compression, filtering, and image geometric transformation such as translation, telescopic, rotation, cutting, etc. Safety Add Watermark and Detect Watermarking Methods to unauthorized third parties are confidential and cannot be easily cracked, even if it is detected by hackers, it cannot be read (digital watermark needs to be encrypted).
In digital watermarking technology, the amount of watermarks and robustness of the watermark constitute a basic contradiction. The ideal watermark algorithm should be hidden in large amounts of data, but also against various channel noise and signal deformation. However, the actual two indicators often cannot be implemented at the same time, but 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.
General models of general digital watermarks include embedding and detection, extracting two phases. Digital watermarking phase, the object of embedded algorithm is the object of the embedded algorithm to find a better fold between digital watermarks in invisible and robustness. The detection phase is mainly designed to detect a detection algorithm corresponding to the embedded process. The result of the detection or the original watermark (such as a string or icon, etc.), or based on the statistical principle test results to determine whether the watermark exists or not. The target of the test solution is to make the probability of the wrong judgment and the leakage. In order to increase the unpredictable difficulty of the attacker, most water-printing schemes currently use the key when adding, and only the key to the key can read the watermark. Second, the origin of digital watermark
Information hide, also known as information camouflage, the word originates from ancient Greece, meaning hidden useful or important information in other information to conceal it, is to secretly hide the secret information to another non-confidential Document content. Cryptography is to study how to protect message content, and camouflage is specializing in how to hide their existence.
The basic ideology of digital watermarking technology is from ancient camouflage (testing). The ancient Greece's Spartan once combined military information on ordinary wooden boards, filled with paraffin, and as long as they fell hot wooden board with fire, they can see secrets after fulating the stone wax. I am afraid that the use of the widest way to write, milk, white, juice, etc. have served as a role of crypto water. About 700 years ago, the watermark on paper appeared in handmade paper technology. 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 password technology, the method has never developed into an independent discipline, which is the lack of the necessary theoretical basis for menstructure.
However, today's development of digital technology is injecting new vitality into ancient subtomy. In the process of studying digital watermarking, the researchers borrowed the idea of information camouflage. Especially in recent years, the development of information hidden technology theory framework research has brought hope to a rigorous science.
Third, the category of digital watermark
Digital watermarking techniques have some of the following divisions from different angles.
Divided according to characteristics
The characteristics of the watermark can be divided into robust digital watermarks and fragile digital watermarks. Robust digital watermarks are mainly used to identify copyright information in digital works. It requires embedded watermarks to undergo a variety of commonly used editing processing; fragile digital watermarks are mainly used for integrity protection, fragile watermarks must be sensitive to signal changes, people Depending on whether the status of the fragile watermark can be judged to be tampered with.
2. Division by the media attached to the watermark
According to the media attached to the watermark, digital watermark is divided into image watermark, audio watermark, video watermark, text watermark, and grid watermark for three-dimensional grid model.
3. Divide the test process
Digital watermarks are divided into bright text prints and blind watermarks by watermarking. 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. Generally, the robustness of the plaintest watermark is relatively strong, but its application is limited by the storage cost. Most of the current digital watermarks are blind watermarks.
4. Divide content according to content
The contents of the digital watermark can be divided into meaningful watermarks and unconscious watermarks. The meaningful watermark refers to the encoding of the watermark itself is also a digital image (such as a trademark) or a digital audio fragment; meaningless watermark only corresponds to a serial number. It is still possible to confirm whether there is a watermark by visual observation due to attack or other reasons. 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 watermarking techniques. About this is introduced later in this article.
6. Point by watermarking hidden location
The hidden position of the digital watermark is divided into time domain digital watermark, frequency domain digital watermark, time / frequency domain digital watermark, and time / scale domain digital watermark. Time domain digital watermarks are superimposed on the signal space, while frequency domain digital watermark, time / frequency domain digital watermark and time / scale domain digital watermarks are in DCT transform domain, time / frequency transform domain, and wavelet transform domain Hidden water printing. With the development of digital watermarking technology, the various watermark algorithms are endless, and the hidden position of watermark is no longer limited to the above four. In fact, as long as a signal transformation is constituted, it is possible to hide watermark on its transform space. Fourth, digital watermark application field
The following several issues that have a universal concern constitute a research background and application field of digital watermarks.
1. Intellectual property protection of digital works
Copyright Identification Watermark is currently studied for a category of digital watermarks due to copy of digital works, and it is very easy to do, and it can be exactly the same as the original work, so the original person has to use some serious damage to the quality of the work to add copyright marks. This obvious visible sign is easily tampered. The owner of the digital work can produce a watermark with a key and embed its original data, and then publicly publish its watermark version. When the work is pirated or a copyright dispute, the owner can obtain a watermark signal from the pirated work or watermarking work, thereby protecting the owner's rights.
The digital watermark technology currently used for copyright protection has entered the initial practical steps, and IBM provides digital watermarking features in its "Digital Library" software. Adobe has also integrated Digimarc companies in its famous Photoshop software. Digital watermark plugin.
2. Bills in business transactions
With the development of high-quality image input and output devices, especially high-precision color inkjet, laser printers and high-precision color copiers, making currency, check, and other pseudo creation make it easier.
It has been reported that the US, Japan, and the Netherlands have begun to study digital watermarking technologies for ticket security. The MIT Media Lab is entrusted by the US Treasury, and has begun to add unique, invisible digital watermarks in each image output by the photocopier output. It can judge the watermark from scanning tickets in real time when needed. There is no, quickly identify authenticity.
In addition, there will be a large excessive electronic file in e-commerce, 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. Title and comments
The title, annotation, etc. of the work (such as photo shooting time and location, etc.) are embedded in the works in the watermark form, which does not require additional bandwidth and is not easily lost.
4. Tamper
Since the existing signal splicing and mosaic technology can be blossomed to pick up the wood without people, the tampering prompt based on digital watermark is an ideal technical way to solve this problem. By hiding the watermark, it can determine whether the sound image signal is tampered with. To achieve this, the original image can usually be divided into multiple separate blocks, and then add each block to different watermarks.
At the same time, the integrity of the work can be determined by detecting the watermark signal in each data block. Unlike other watermarks, such watermarks must be fragile, and when the watermark signal is detected, it does not require raw data.
5. Use control
A typical example of such an application is a DVD anti-copy system that adds the watermark information to the DVD data so that the DVD player can determine its legitimacy and copyability by detecting watermark information in the DVD data. To protect manufacturers' business benefits.
6. Concealed communication and its confrontation
The information hidden technology relying on digital watermark not only provides a security approach to non-passwords, but also the revolution of the network intelligence war. The network intelligence war is an important part of the information war, and its core content is to use public network to confidential data transmission. Since encrypted documents are often confusing, it is easy to pay attention to attackers. The wide application of network multimedia technology has made a new idea using public networks, using digital sound image signals with respect to human visual, auditory redundancy, and can be hidden in various information, thereby implementing concealed communication. V. Research status and development prospects for digital watermarking technology
The study of my country's academic community on digital watermarking technology is also in the ascendant, and there is a considerable number of research institutions to invest in this area, and some have achieved important research results. Implementation hidden and digital watermarking technology As a frontier research, it is closely related to information security, information hiding, data encryption. In particular, today's research on digital watermarking technology is more practical in today's rapid development of network technology and applications.
Digital Watermarking Studies must be widely used for all data files to be used in Internet, including JPEG compressed images, MPEG2 compressed video, WAV, MIDI, MP3 audio files, AVI, and 3D animation files, PS and PDF standard text, Voice-Mail or Video-mail and other multimedia mail formats.
The digital watermarking technology derived from ancient subparatic abparators will be widely used in information security in the information age.
