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Watermarking & Steganography

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1 Watermarking & Steganography
MIS 604 – IT Solutions to Business Problems Spring 2002 Introduction In the last few years we have made tremendous progress in the use of digital technologies. Digital distribution of information has become a corner stone of the world wide web that we know of today. The electronic media is becoming popular for transmission and storage of documents, images, audio, video and other types of information. Information stored in digital format can be copied without quality loss and distributed efficiently at fairly low cost. This however has also led to an increased potential for misuse and unauthorized distribution of information in violation of copyright law. The issues regarding copyright infringement are well publicized via the legal shenanigans between the music industry and Napster and eventually led to shutdown of the very popular music exchange website. Apart from this highflying case plagiarism and theft of information at a smaller scale has become very rampant. Watermarking assists in establishing the identity and preserving the ownership of the digital information. We already know what cryptography is. Before we start of Watermarking and Steganography let us try to understand the difference between the three.

2 Cryptograpy & Steganography vs. Watermarking
Cryptography is about protecting the content of messages (their meaning). Steganography is about concealing the existence of messages Watermarking is about establishing identity of information to prevent unauthorized use They are imperceptible They are inseparable from the works they are embedded in They remain embedded in the work even during transformation While cryptography is about protecting the content of messages (their meaning), steganography is about concealing their very existence. It comes from Greek roots, literally means 'covered writing', and is usually interpreted to mean hiding information in other information. Examples include sending a message to a spy by marking certain letters in a newspaper using invisible ink, and adding sub-perceptible echo at certain places in an audio recording. It is often thought that communications may be secured by encrypting the traffic, but this has rarely been adequate in practice. Æneas the Tactician, and other classical writers, concentrated on methods for hiding messages rather than for enciphering them; and although modern cryptographic techniques started to develop during the Renaissance, we find in 1641 that John Wilkins still preferred hiding over ciphering because it arouses less suspicion. This preference persists in many operational contexts to this day. For example, an encrypted message between a known drug dealer and somebody not yet under suspicion, or between an employee of a defense contractor and the embassy of a hostile power, has obvious implications. As the purpose of steganography is having a covert communication between two parties whose existence is unknown to a possible attacker, a successful attack consists in detecting the existence of this communication (e.g., using statistical analysis of images with and without hidden information). Watermarking, as opposed to steganography, has the (additional) requirement of robustness against possible attacks. In this context, the term 'robustness' is still not very clear; it mainly depends on the application. Copyright marks do not always need to be hidden, as some systems use visible digital watermarks, but most of the literature has focused on imperceptible (e.g., invisible, inaudible) digital watermarks which have wider applications. Visible digital watermarks are strongly linked to the original paper watermarks which appeared at the end of the XIII century to differentiate paper makers of that time. Modern visible watermarks may be visual patterns (e.g., a company logo or copyright sign) overlaid on digital images. The intent of use is also different: the payload of a watermark can be perceived as an attribute of the cover-signal (e.g., copyright information, license, ownership, etc.). In most cases the information hidden using steganographic techniques is not related at all to the cover. These differences in goal lead to very different hiding techniques.

3 Watermarking Watermarking is the practice of hiding a message about an image, audio clip, or other work of media within the work itself. Watermark is hidden from the user in normal use Watermark becomes visible as a result of a special viewing process

4 Watermarking - Examples
Sending a message to a spy by marking certain letters in a newspaper using invisible ink Adding sub-perceptible echo at certain places in an audio recording. Embedding a picture of President Andrew Jackson into the paper during paper making process. The main driving force is concern over protecting copyright; as audio, video and other works become available in digital form, it may be that the ease with which perfect copies can be made will lead to large-scale unauthorized copying which will undermine the music, film, book and software publishing industries. There has therefore been significant recent research into ‘watermarking’ (hidden copyright messages) and ‘fingerprinting’ (hidden serial numbers or a set of characteristics that tend to distinguish an object from other similar objects); the idea is that the latter can be used to detect copyright violators and the former to prosecute them

5 Watermarking – Examples
“In 1981, photographic reprints of confidential British Cabinet Documents were being printed in newspapers. Rumor has it that to determine the source of the leak, Margaret Thatcher arranged to distribute uniquely identifiable copies of the documents to each of the ministers. Each copy had a different word spacing that was used to encode the identity of the recipient.” - Digital Watermarking, Cox A digital watermark is a digital signal or pattern inserted into a digital image. Since this signal or pattern is present in each unaltered copy of the original image, the digital watermark may also serve as a digital signature for the copies. A given watermark may be unique to each copy (e.g., to identify the intended recipient), or be common to multiple copies (e.g., to identify the document source). In either case, the watermarking of the document involves the transformation of the original into another form. This distinguishes digital watermarking from digital fingerprinting where the original file remains intact, but another file is created that "describes" the original file's content. As a simple example, the checksum field for a disk sector would be a fingerprint of the preceding block of data. Similarly, hash algorithms produce fingerprint files. Digital watermarking is also to be contrasted with public-key encryption, which also transform original files into another form. It is a common practice nowadays to encrypt digital documents so that they become un-viewable without the decryption key. Unlike encryption, however, digital watermarking leaves the original image or (or file) basically intact and recognizable. In addition, digital watermarks, as signatures, may not be validated without special software. Further, decrypted documents are free of any residual effects of encryption, whereas digital watermarks are designed to be persistent in viewing, printing, or subsequent re-transmission or dissemination.

6 Digital Watermarking A digital watermark is a digital signal or pattern inserted into a digital image. “In 1981, photographic reprints of confidential British Cabinet Documents were being printed in newspapers. Rumor has it that to determine the source of the leak, Margaret Thatcher arranged to distribute uniquely identifiable copies of the documents to each of the ministers. Each copy had a different word spacing that was used to encode the identity of the recipient.” - Digital Watermarking, Cox A digital watermark is a digital signal or pattern inserted into a digital image. Since this signal or pattern is present in each unaltered copy of the original image, the digital watermark may also serve as a digital signature for the copies. A given watermark may be unique to each copy (e.g., to identify the intended recipient), or be common to multiple copies (e.g., to identify the document source). In either case, the watermarking of the document involves the transformation of the original into another form. This distinguishes digital watermarking from digital fingerprinting where the original file remains intact, but another file is created that "describes" the original file's content. As a simple example, the checksum field for a disk sector would be a fingerprint of the preceding block of data. Similarly, hash algorithms produce fingerprint files. Digital watermarking is also to be contrasted with public-key encryption, which also transform original files into another form. It is a common practice nowadays to encrypt digital documents so that they become un-viewable without the decryption key. Unlike encryption, however, digital watermarking leaves the original image or (or file) basically intact and recognizable. In addition, digital watermarks, as signatures, may not be validated without special software. Further, decrypted documents are free of any residual effects of encryption, whereas digital watermarks are designed to be persistent in viewing, printing, or subsequent re-transmission or dissemination.

7 Watermarking - Applications
In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission Two kinds of monitoring systems exist Passive Monitoring: Recognize the content being broadcast Compares received signals against a database of known content Very expensive as large frames need to be compared Useful for monitoring of competition Active Monitoring: Rely on information that is broadcast along with the content Relatively easier to implement Identification information is easily to interpret Requires cooperation of broadcasting mechanism In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

8 Watermarking – Owner Identification
Under US law the creator of a story, painting, song, or any other original work holds copyright the instant it is recorded in some physical form Up to 1998 a copyright notice was required to be attached to each distributed copy if the owner wanted to protect his/her rights Even after the change in 1998 when this is no longer required the awards are reduced significantly if the copyright information is not present with the work Textual Copyright notices have several limitations They are easy to remove deliberately or inadvertently They can be aesthetically ugly if they cover a part of the image For music the copyright is only on the media not on the work Electronic watermarks are imperceptible and inseparable from the work they are contained and are hence superior In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

9 Watermarking – Proof of Ownership
Textual notices can be erased and replaced by a forger Image editors can be used to edit copyright notices One solution is to register the image with copyright depository (expensive) Watermarking can prove image identity Watermarks may also be altered It is possible to prove that one image is derived from another indirectly proving the ownership In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

10 Watermarking – Other Applications
Transaction Tracking Content Authentication Copy Control Device Control In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

11 Image Watermarking – Properties
Should be perceptually invisible to prevent obstruction of the original image. Statistically invisible so it cannot be detected or erased. Simple to extract watermark from image Otherwise, the detection process requires too much computation time. Detection should be accurate. Few false positives & false negatives Should be able to produce numerous watermarks. Otherwise, only a limited number of images may be marked. Should be robust to filtering, additive noise, compression, and other forms of image manipulation. Should be able to determine the true owner of the image. In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

12 Watermarking – Process
In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner. Reference:

13 Image Watermarking – Techniques
M-Sequence Generator Embedded or added to the last significant digit of the original image Watermark was extracted by taking the least significant bits at specific locations Detection was done by cross correlation of the original and extracted watermarks Discrete Cosine Transform (DCT) Watermark was placed in perpetually significant areas of the image Watermark based on 1000 random samples of a N(0,1) distribution Sample was added to the 1000 largest DCT coefficients of the image Inverse DCT was taken to retrieve the watermarked image For detection watermark was extracted from the DCT of suspected image In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

14 Image Watermarking – Techniques
Discrete Wavelet Transform(DWT) Watermark modeled as Gaussian noise was added to middle and high frequency bands of the image Decoding process involved taking DWT of potentially marked image Fractal Codes A collage map was composed from 8x8 blocks of original image and from image’s DCT In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

15 Watermark - Image In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

16 Watermark - Image In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

17 Watermarking – Audio Properties
Perceptually inaudible, such that no perceptual quality degradation occurs Statistically undetectable To ensure security Cannot be removed or modified by any signal processing operation (e.g. filtering, compression, MP3-encoding,...) without degrading perceptual quality Readily extractable to detect copyright information In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

18 Watermarking – Audio Techniques
Echo Coding Phase Coding Direct-Sequence Spread Spectrum Frequency-Hopped Spread Spectrum Frequency Masking In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

19 Watermark - Audio Wideband Audio Signal is a raw WAV file
Original Sound Original Sound Watermarked Sound Watermarked Sound Echo Coding Frequency Hopped Spread Spectrum Wideband Audio Signal is a raw WAV file Ten seconds in length Sampled at 44.1 kHz Quantized to 16 bits per sample In 1997 a scandal broke out in Japan regarding television advertising. At least two stations had been routinely overbooking time. Advertisers were paying for thousands of commercials which were never aired. This practice remained undetected for more than 20 years since there were no systems in place to actually monitor broadcasts. In a broadcast monitoring system identifying data is added to the video/audio signal prior to transmission by terrestrial, cable and satellite broadcasters. These identifiers are imperceptible to television/radio audiences and survive all common video/audio-processing operations. Broadcasts can then be monitored to verify both that program and advertisement transmissions comply with contractual requirements and that transmissions do not occur without the permission of the broadcast owner.

20 Steganography The word steganography comes from the Greek steganos , meaning covered or secret, and graphy , meaning writing or drawing. Therefore, steganography literally means covered writing. Steganography simply takes one piece of information and hides it within another Computer files (images, sounds recordings, even disks) contain unused or insignificant areas of data Steganography takes advantage of these areas, replacing them with information (encrypted mail, for instance). The files can then be exchanged without anyone knowing what really lies inside of them An image of the space shuttle landing might contain a private letter to a friend. Rumor has it that terrorists used steganography to transmit messages to one another. (http://www.wired.com/news/politics/0,1283,41658,00.html) Reference: Steganography simply takes one piece of information and hides it within another. Computer files (images, sounds recordings, even disks) contain unused or insignificant areas of data. Steganography takes advantage of these areas, replacing them with information (encrypted mail, for instance). The files can then be exchanged without anyone knowing what really lies inside of them. An image of the space shuttle landing might contain a private letter to a friend. A recording of a short sentence might contain your company's plans for a secret new product. Steganography can also be used to place a hidden "trademark" in images, music, and software, a technique referred to as watermarking. Reference:

21 Steganography – Early Examples
In his history of the Persian Wars, Herodotus tells of a messenger who shaved his head and allowed a secret message to be tattooed on his scalp. He waited until his hair grew back. Then he journeyed to where the recipient awaited him and shaved his head again. The message was revealed. It was history’s first use of steganography.

22 Steganography – Invisible Ink
Ancient Romans used to write between lines using invisible ink based on various natural substances such as fruit juices, urine, and milk. Their experience was not forgotten: even nowadays children play spies and write secret messages that appear only when heated.

23 Steganography – Invisible Ink
During the World War II the Germans developed the microdot. A secret message was photographically reduced to the size of a period, and affixed as the dot for the letter 'i' or other punctuation on a paper containing a written message. Microdots permitted the transmission of large amounts of printed data, including technical drawings, and the fact of the transmission was effectively hidden.

24 Principles of Steganography
Computer Steganography is based on two principles. The first one is that the files containing digitized images or sound can be altered to a certain extend without loosing their functionality. The other principle deals with the human inability to distinguish minor changes in image color or sound quality, which is especially easy to make use of in objects that contain redundant information, be it 16-bit sound, 8-bit or even better 24-bit image. The value of the least significant bit of the pixel color won’t result in any perceivable change of that color.

25 Steganography Process
The data to be concealed is compressed and hidden within another file. The first stem is to file a which will used to hide the message (also called a carrier or a container.) The next step is to embed the message one wants to hide within the carrier using a steganographic technique. Two different techniques commonly used for embedding are: Replace the least significant bit of each byte in the [carrier] with a single bit for the hidden message. Select certain bytes in which to embed the message using a random number generator; resampling the bytes to pixel mapping to preserve color scheme, in the case of an image...; hiding information in the coefficients of the discrete cosine, fractal or wavelet transform of an image; and applying mimic functions that adapt bit pattern to a given statistical distribution." The data to be concealed is compressed and hidden within another file. The hidden message may be placed inside: the white space of text messages the dark areas of a photographic image within the unused portions of a digital file format. The first item needed for steganography is called a carrier or a container. This can be a text file, graphic file or sound file which will host the message that is desired to be hidden. The carrier or container is innocent looking so that it does not arouse the suspicion of anyone viewing it. The next step is to embed the message one wants to hide within the carrier using a steganographic technique. Techniques Replace the least significant bit of each byte in the [carrier] with a single bit for the hidden message. Selecting certain bytes in which to embed the message using a random number generator; resampling the bytes to pixel mapping to preserve color scheme, in the case of an image...; hiding information in the coefficients of the discrete cosine, fractal or wavelet transform of an image; and applying mimic functions that adapt bit pattern to a given statistical distribution."

26 Steganography Software
EZStego (Stego Online, Stego Shareware, Romana Machado) Java based software program which supports only GIF and PICT formats; Gif-It-Up v1.0 (Lee Nelson) A stego program for Windows 95 that hides data in GIF files Hide and Seek (Colin Maroney) can hide any data into GIF images; JPEG-JSTEG (Derek Upham) can hide data inside a JPEG file MP3Stego (Fabien A.P. Petitcolas, Computer Laboratory, University of Cambridge) can hide data inside MP3 sound files; Steganos (Demcom, Frankfurt, Germany) encrypts files and then hides them within BMP, DIB, VOC, WAV, ASCII and HTML files. Reference:http://www.antichildporn.org/steganog.html

27 Steganography Software – S-Tools
S-Tools is one of the most popular steganography tools. This program is Windows 95/98 compatible It has the ability to conceal files within BMP, GIF and WAV files. Allows you to simply point and click your way to hiding files. It also has the ability to hide multiple files in one container. It has been updated each year and can be easily downloaded by anyone. (http://members.tripod.com/steganography/stego/software.html) Dear Susan: I can wait no longer I want to see you now please say that you will come. San...

28 Steganalysis Steganalysis is the art of discovering and rendering useless such covert messages. Steganalysis involves analysis of the carrier file Simpler steganographic techniques produce some discernible change in the file size, statistics or both. These changes can manifest themselves in color variations, loss of resolution and other distortions that are visible to the human eye. This form of detection requires that you know what the original carrier image or file should look like.

29 Fingerprinting


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