Source: - Bo Xiaochen Shen Lin Cheng Changwensen
---- As the eyes and ears of the feeling of the organ, it is not perfect, and many of them can be digitally available.
Defects used by technology. In recent years, the rapid development of cognitive science has laid a physiological basis for digital watermarking technology.
The color sensation and brightness adaptability of the human eye, the parental phase perception defects provide possible information on information hidden implementation
way. On the other hand, the relevant disciplines such as informationism, cryptography provide rich theoretical resources for digital watermarking technology.
Multimedia data compression coding provides the necessary technical foundation for digital watermarking.
---- The most vital research topic is often at the position of multidisciplinary intersection, the digital watermark is such a
It involves multiple fields covering a variety of technologies.
Three research levels
---- Similar to other technologies, digital watermarking can also be divided into basic theory research, application basic research
And application research three levels.
----1. Basic theory research
---- The purpose of digital watermark basic research is to establish the theoretical framework of digital watermarking, solve the watermark information analysis.
Basic theoretical issues such as concealedness descriptions.
---- Digital water is derived from ancient neckout. For a long time, write technology is always due to lack of theoretical basis.
There is no development into a discipline. However, on the basis of cognitive science and signal processing theory, fully borrowed from cryptography
As, we can establish the theoretical framework of digital watermarking technology, analyze the relationship between data volume and concealedness, so that
After a given data to be protected, you can have a reliable standard to select a watermark plan, and can comprehensively judge various
The advantages and weakness of the digital water printing algorithm.
----2. Applied Basic Research
---- The main direction of application basic research is for multimedia signals such as images, sounds, video, research corresponding
Watermark hidden and decoding algorithm, and resisting affine transformation, filtering, heavy sampling, color jitter, lossless compression
Robust digital watermarking technology.
---- 3. Application research
---- Application study is based on the practical purpose of watermarking technology, and studies various standard multimedia data file formats.
Watermarking algorithm. Watermark application research specifically to all data files used in Internet, including JPEG pressure
Shrink images, MPEG2 compressed video, WAV, MIDI, MP3 audio file, AVI and 3D animation file, PS and PDF standard
Quasi-text, Voicemail or Video -mail and other multimedia mail formats.
---- In addition, in order to preempt the lead, pay attention to research on multimedia data files that have not yet formed standards
Watermark algorithm, such as a new generation of video compression standard MPEG4, various streaming media files, etc.
---- Bill anti-counterfeiting is also an important application area of digital watermarks, and various anti-counterfeiting tickets are not studied.
By neglect.
Theoretical model and credit analysis
---- In the information theory, Shannon's channel formula and confidential communication formula has always been communication science
Compass for development, although many of the conclusions in the informationism are, some fakes
It is also far from the actual situation, but their guidance on communication technology is undeniable. Digital water
Printing in applications should also solve some key theoretical issues, but have not yet been able to guide like scented scented formulas.
The Basic Theory of Disciplinary Development.
---- The credit analysis of digital watermarks should answer such a question: "The data file and hidden required for the need to protected
How much hidden watermark information can you join? "Only solving this problem can we be scientifically designed
The data format of the printed logo.
---- Currently, by modeling the statistical distribution of the Fourier transform domain and the DCT transform domain coefficient,
Some signal detection theory, the academic community has got some credit estimation results of typical digital watermarking algorithms, but as
A complete theoretical description, these results lack convincing.
Typical algorithm
---- Digital Watermarking Technology across signal processing, digital communication, cryptography, pattern identification, etc.
Researchers in various fields have unique research perspectives, and its algorithm can be described as a five-flowers. There are several of the following:
----1. Minimum significant bit algorithm (LSB)
---- Minimum Active Bit Algorithm (LSB) is the first for L.f.Turner and R.van Schyndel et al.
Digital watermarking algorithm is a typical spatial domain information hidden algorithm.
---- LSB algorithm uses a specific key to generate a random signal through the M sequence generator, then press a certain rule
The 2D watermark signal is arranged, and the lowest position of the original image corresponding pixel value is inserted one by one. Due to watermark signals
Hidden at the lowest position, equivalent to superimposing a weak signal, so it is difficult to detect in vision and auditory.
The detection of the LSB watermark is achieved by the relevant operations and statistical decisions of the image to be tested and the watermark image. Stego DOS,
Early Digital Water Printing Algorithms such as White Noise Storm, Stools have used the LSB algorithm.
---- LSB algorithm can hide more information, but hidden information can be easily removed, can't be full
The robust requirements of the digital watermark, so the current digital watermark software has rarely use the LSB algorithm. but,
As a large amount of information hiding, the LSB still occupies a considerable status in hidden communications.
----2. PatchWork algorithm
---- PatchWork is a digital water proposed by the MIT Media Laboratory Walter Bander et al.
Printing algorithm, mainly used to print the ban.
---- PatchWork digital watermark hidden in the statistical characteristics of a particular image area, it is strong,
In effectively, the defect is low in data volume, and the affine transform is sensitive.
Sense, the resistance to multiple copies is weak.
---- 3. Texture block mapping coding
---- Texture block mapping to hide the watermark information in the random texture area of the image, using the similarity between textures
Cover the watermark information. This algorithm has resistance to filtering, compression, and twisting, but requires artificial intervention.
---- 4. Text fine-tuning algorithm
---- Text fine-tuning algorithm is used to hide digital watermarks in PS or PDF documents, mainly by slight change words
Method such as spacing, line spacing, and character characteristics, etc. to embed watermark. This watermark can resist attacks, and its security is mainly
Concealation is guaranteed.
---- 5. DCT transform domain digital watermarking algorithm
---- DCT transform domain digital watermark is the most research on the most digital watermark, it has robustness, hidden
Good tobath. Its main thinking is to select a medium low frequency system in the DCT transform field of the image. It
So, the low frequency coefficient is because the feeling of the human eye is mainly concentrated in this frequency, and the attacker is destroying the watermark.
In the process, it is inevitable that the serious decline in image quality can not be caused, and the general image processing process will not change this.
Data.
---- Due to the core of the compression algorithm of JPEG, MPEG is quantified in the DCT transform field,
After cleverly fusion the water printing process and the quantization process, the watermark can be protected against lossy compression. In addition, DCT transform domain
The number of statistical distributions have a better mathematical model that can estimate the amount of watermarks in theoretically.
---- 6. Direct sequence spreading water printing algorithm
---- The spread rate of the watermarking algorithm is the application of spread spectrum communication technology in digital watermark. Traditional narrowband modulation communication
Different, spread spectrum communication will be spread in a very wide frequency band after the information to be transmitted is distributed in a very wide frequency band.
Pseudo random characteristics. The acceptor is despreaded by the corresponding spreading code to obtain real transmission information.
---- spread frequency communication has strong anti-interference, highly confidentiality, widely used in military applications. In fact,
The spread spectrum communications can also be regarded as a radio method. The theoretical basis for throwing its information theory is not to talk,
The perceived angle is considered that spread spectrum communications has confidentiality, that is, it disguised information to channel noise, making people unable to distinguish.
---- The spreading watermark method is similar to the spread spectrum communication, and it is superimposed in the original data after spreading the watermark information.
on. From the frequency domain, the watermark information is spread on the entire spectrum and cannot be recovered through the general filtering means. If you want to attack
When the watermark information must be added to all bands, it will undoubtedly seriously damaging the quality of the original data.
the amount.
---- 7. Other transform domain Digital Water Printing Algorithm
---- Transform domain digital watermark is not limited to DCT transform domain or Fourier profile, as long as it can hide water printing well
Information, all signal transforms are feasible. In recent years, many scholars have tried to use wavelet transform or other time / frequently
The means of analyzes, hidden the digital watermark information in the time / scale or time / frequency domain, and has achieved a better effect.
Attack and test
---- Similar to cryptography, digital watermarks are also a confrontational research area. It is because there is a watermark attack
The existence of the watermark studies have been continuously in-depth. In addition, in order to realize the standardization of digital watermark, you must
Word water printing algorithm for safety testing. Watermark testers need to be familiar with the watermark algorithm, but also to be familiar with the watermark attack algorithm.
Moreover, the quantitative analysis of watermark information and robustness will be made from the theory of the watermark algorithm.
----1. Watermark attack classification
---- Watermark attack is the same as password attacks, including active attacks and passive attacks. The purpose of active attack is not
It is cracking digital watermark, but tampered with or destroyed watermarks, allowing legal users to read watermark information. Passive attack
Then try to crack the digital watermarking algorithm. In contrast, the difficulty of passive attacks is much larger, but once successful, all
The data encrypted by the watermark algorithm has lost safety. The hazard of active attack is not ashamed for the harm of passive attacks.
Big, but its attack method is often very simple, easy to spread widely. Whether it is cryptographic or digital watermark, active attack
Hit is a headache problem. For digital watermarks, most of the attacks are active attacks.
---- It is worth mentioning that active attacks are not equal to the destruction. Take copyright protection watermark as an example, if will
The digital artwork embedded in the watermark has made an unrecognizable, and there is no benefit of the attacker because of the destroyed artwork.
It is unable to sell. For ticket security watermarks, the quality of excessive damage data is meaningless. Real master
The watermark attack should be removed without more influential data quality.
---- Password attack is generally divided into a Ciphertext-ITATACK, selecting a plaintext attack
(Chosen Plaintext Attack) and known clear text attacks. Refer to password
The concept can define several situations of watermark attacks.
---- (1) Reipient Write Attack (Stego -only Attack)
---- Reipient writing attack means that the attacker has received data containing watermarks and does not understand the content of the watermark.
It is the most common situation.
---- (2) Know-Cover Attack (KNOW-Cover Attack)
---- Known masked information attack means that an attacker not only has a data containing watermark, but also not
The original data containing watermarks is obviously what attackers want.
---- (3) known watermark attack (KNOWN-Message Attack)
---- Some attackers often pretend to be legal users in order to crack watermarks, they have some known watermarks.
Data, then analyze the location of the watermark hidden. This kind of attack is very similar to the known clear text attack in cryptography.
---- (4) Choose Write Attack (Chosen-Stego Attack)
---- If an attacker gets the watermark embedding software, you can try to embed various information in the media data, thereby constituting the selection of the method of writing attacks, which is the most promising attack.
---- 2. Typical active watermark attack method
---- As mentioned earlier, cracking the digital watermarking algorithm is very difficult, in practical applications, watermarks are mainly faced.
Active attack.
---- Various types of digital water printers have their own weaknesses, for example, time domain spread spectrum hidden synchronization
The requirements are strict, destroy their synchronization (such as data interpolation), can make the watermark detector can be invalidated. Typical active watermark
Attack methods include:
---- (1) Multiple copy average
---- A plurality of distribution versions of the same work are valued, and the watermark is removed by watermarking.
---- (2) Various linear filters
---- For the frequency domain watermark algorithm, a linear filter having a specific frequency characteristic can be constructed to attack the frequency domain
Hidden watermark information.
---- (3) Geometric deformation attack
---- Through a slight geometric deformation, you can damage the synchronization of the data, and it does not affect the data quality.
Quantity, but the digital watermarking algorithm for many direct expansion sequence moduls is threatened.
---- (4) Nonlinear filtering
---- Medium value filtering or other sequential statistical filtering can either change the frequency domain characteristics of the signal, but also destroy
Synchronization is a composite attack.
---- (5) Splicing attack
---- Splicing attack is to divide a digital work containing watermark into several small pieces, form a number of separate documents,
Then put it on the web page. Since the various digital water printers have a certain decoding space, only by a small amount of data
It is difficult to read watermarks, so it is difficult to resist splicing attacks.
---- (7) Second or multiple watermark attacks
---- An attacker uses your own algorithm to add watermarks in digital works, even if this operation cannot be destroyed
Watermarking, also causes chaos of the watermark identification, thereby bringing difficulties to judicial identification. Especially for no original numbers
According to the blind watermark system for testing, it is generally difficult to determine which watermark operation is in front, which one is behind.
---- 3. Watermark test
---- In order to finalize the technical standards of watermarking, the information security assessment agency must be impressive for a large number of open water.
The method was tested. This test is not only experimental, but also the theoretical analysis, so as not to be wrong due to sample selection.
The mistake is prevacted.
---- Face a large and cumbersome test experiment, the research of digital watermark automatic test system is very necessary
want. The Stirmark software developed by Cambridge University is a typical digital watermark test system, which integrates dozens of kinds.
The watermark attack algorithm can compare robustness of the watermarking algorithm.
---- For a digital watermark that has a standard, at least it is at least to test the several aspects:
---- (1) concealment
---- There is a contradiction between the amount of information and concealedness of digital watermarks, with the increase of watermark information, works
The quality is inevitable. Incidental testing requires assessment of the information and visibility of the watermark algorithm, give water
Accurate relationship between the amount and data degradation.
---- Assessment of multimedia data quality such as images, sounds cannot be based only on signal-to-noise ratio, peak signal-to-noise ratio, etc.
Indicators in signal processing must rely on visual and auditory physiological models, otherwise it will not have scientific, which is not only
Digital watermarks are also one of the basic guidelines for data compression.
---- (2) Robust
---- Robust Test is actually an active attack process, mainly testing digital watermarks for data synchronization
Lai level, resistance to various linear and nonlinear filtering, and other attacks such as geometric conversion.
---- (3) Safety
---- Safety Test is mainly to evaluate the time and complexity of the breaking water printing algorithm, and this is used as an indicator of watermarking.
---- Digital Watermarking Technology From the beginning, it is a variety of technologies integrated research, from communication,
Researchers in the fields of pattern recognition, information security each have explored from different research perspectives, forming a hundred flowers
Put, a lot of money. As a new research area, digital watermarks have a large number of theoretical and engineering issues.
To resolve. I believe that with the deep research work, the digital watermark will gradually mature, and finally form a special
Independent technical discipline.
