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Reza Mohammadi Shiraz University Of Technology

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1 Reza Mohammadi Shiraz University Of Technology
In The Name Of God Digital WaterMarking Reza Mohammadi Shiraz University Of Technology R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING

2 Outline Information Hiding Concept & History Digital Watermarking
Digital Watermarking Types Watermarking Algorithm Requirements Digital Watermarking Techniques Digital Watermarking Applications References R.MOHAMMADI DIGITAL WATERMARKING

3 Information Hiding Information Hiding…..started with
Steganography (art of hidden writing): The art and science of writing hidden messages in such a way that no one apart from the intended recipient knows of the existence of the message. The existence of information is secret. Stego – Hidden , Graphy – Writing  ‘art of hidden writing’ R.MOHAMMADI DIGITAL WATERMARKING

4 History 440 B.C. 1st and 2nd World Wars Current
REZA MOHAMMADI 440 B.C. Histiaeus shaved the head of his most trusted slave and tattooed it with a message which disappeared after the hair had regrown. To instigate a revolt against Persians. 1st and 2nd World Wars German spies used invisible ink to print very small dots on letters. Current Special inks are used to write a hidden messages on bank notes. Industry demands for digital watermarking and fingerprinting of audio and video. Greek tyrant Histiaeus was held prisoner, 5th century BC, he had to send a secret message to his son-in law Aristagoras in Miletue. Histiaeus shaved the head of a slave and tattooed a message on his scalp. When the slave's hair had grown long he was dispatched to Miletus. R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING

5 The Need for Data Hiding
Covert communication using images (secret message is hidden in a carrier image) Ownership of digital images, authentication, copyright Data integrity, fraud detection, self-correcting images Adding captions to images, additional information, such as subtitles, to video, embedding subtitles or audio tracks to video (video-in-video) Intelligent browsers, automatic copyright information, viewing a movie in a given rated version Copy control (secondary protection for DVD) R.MOHAMMADI DIGITAL WATERMARKING

6 (covered writing, covert channels)
REZA MOHAMMADI Introduction Steganography (covered writing, covert channels) Protection against detection (data hiding) Protection against removal (document marking) Fingerprinting (identify all objects, every object is marked specific) Watermarking (all objects are marked in the same way) WATERMARKING

7 Digital Watermarking A technique which allows an individual to add hidden copyright notices or other verification messages to digital audio, video, or image signals and documents. Water mark :A mark, which is imperceptibly added to the cover-signal in order to convey the hidden data. The technique takes its name from watermarking of paper or money as a security measure. While the addition of the hidden message to the signal does not restrict that signal's use, it provides a mechanism to track the signal to the original owner. R.MOHAMMADI DIGITAL WATERMARKING

Differences between steganography and watermarking are both subtle and essential. The main goal of steganography is to hide a message m in some audio or video (cover) data d, to obtain new data d', practically indistinguishable from d, by people, in such a way that an eavesdropper cannot detect the presence of m in d'. The main goal of watermarking is to hide a message m in some audio or video (cover) data d, to obtain new data d', practically indistinguishable from d, by people, in such a way that an eavesdropper cannot remove or replace m in d'. It is also often said that the goal of steganography is to hide a message in one-to-one communications and the goal of watermarking is to hide message in one-to-many communications. R.MOHAMMADI DIGITAL WATERMARKING

9 Watermarking Algorithm Design Requirements
As much information (watermarks) as possible  Capacity Only be accessible by authorized parties  Security Resistance against hostile/user dependent changes  Robustness Invisibility  Imperceptibility R.MOHAMMADI DIGITAL WATERMARKING

10 Two Types of Digital Watermarks
REZA MOHAMMADI Visible watermarks change the signal altogether such that the watermarked signal is totally different from the actual signal In visible digital watermarking, the information is visible in the picture or video. Typically, the information is text or a logo, which identifies the owner of the media. The image on the right has a visible watermark. When a television broadcaster adds its logo to the corner of transmitted video, this also is a visible watermark. e.g., adding an image as a watermark to another image. R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING


12 Two Types of Digital Watermarks
REZA MOHAMMADI Two Types of Digital Watermarks B. Invisible watermarks do not change the signal to a perceptually great extent, i.e., there are only minor variations in the output signal. In invisible digital watermarking, information is added as digital data to audio, picture, or video, but it cannot be perceived as such (although it may be possible to detect that some amount of information is hidden in the signal). An example of an invisible watermark is when some bits are added to an image modifying only its least significant bits. R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING

13 Invisible Watermark REZA MOHAMMADI Suppose this is the original image
And this is the watermark When I apply this watermark to the original image, there is no perceptible change! But if I use special tools, I shall be able to distinguish the watermark. R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING

14 Basic Principle in Steganography/Watermarking
REZA MOHAMMADI Basic Principle in Steganography/Watermarking Secret Image Stego Object Cover Image Encoder Key Decoder Secret Image Communications Channel Original Cover R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING

15 Watermarking Process Data (D), Watermark (W), Stego Key (K), Watermarked Data (Dw) Embed (D, W, K) = Dw Extract (Dw) = W’ and compare with W (e.g. find the linear correlation and compare it to a threshold) Q. How do we make this system secure ? A. K is secret (Use cryptography to make information hidden more secure) R.MOHAMMADI DIGITAL WATERMARKING

16 Watermarking Techniques
REZA MOHAMMADI Watermarking Techniques Binary Files Text Document XML Images LSB, DCT, Wavelet Audio Midi, MP3 Other Types WATERMARKING 1 1

17 Information Hiding in Binary Files
REZA MOHAMMADI Information Hiding in Binary Files If we change or remove something in a binary file, execution could be different. We can use a serial key or authors logo to achieve copyright protection. Cracks and key generators are widely available for common programs. Method for watermarking the binary source: b, c, d must be done in same order, but a can be executed at any time. a = 2; b = 3; c = b + 3; c = b +3; d = b +c; d = b + c; Also known as marking WATERMARKING

18 Information Hiding in Binary Files
REZA MOHAMMADI Information Hiding in Binary Files W = {w1, w2, w3, w4, ....., wn} (Watermark) wi Є {0, 1} Divide program into n blocks. 0 = code left unchanged, 1 = two instructions are switched. To decode we need the original binary file. Comparing the original and marked binary files, we can recover W. Not resistant to attacks. If the attacker has enough copies, he can recover W. Also known as marking R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING

19 Information Hiding in Documents
REZA MOHAMMADI Information Hiding in Documents Originals and photocopied materials look different on paper. Electronic originals and copied materials are identical. Data hiding in documents uses embedded marks. Marks can be same or different on all copies. Can be achieved by: Altering text formatting, Altering characteristics of characters. Alterations not visible but decodable. Also known as marking R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING

20 Information Hiding in Documents
REZA MOHAMMADI Information Hiding in Documents General protocol in document hiding. A page of doc is represented by a function, f. Codeword assigned to document decides which line is to be altered. Differential Encoding Technique generally used. Require a encoder and decoder. Also known as marking Codebook Encoder Marked Documents Original Document WATERMARKING

21 Information Hiding in Documents
REZA MOHAMMADI Information Hiding in Documents One of three techniques are applied to hiding data: Line Shift Coding - Vertical shifting of lines Word Shift Coding - Horizontal spacing between each word In this example the first line uses normal spacing while the second has had each word shifted left or right by 0.5 points in order to encode the sequence , that is 65, the ASCII character code for A. Shifts lines up slightly up or down h-i Shifted up slightly h+i Lines to be shifted decided by Codebook Also known as marking R.MOHAMMADI DIGITAL WATERMARKING WATERMARKING

22 Text Techniques White Space manipulation
REZA MOHAMMADI Text Techniques White Space manipulation Text viewers can’t see white space at the end of lines. Using a document’s grammar to hide information “The auto drives fast on a slippery road over the hill” changed to “Over the slope the car travels quickly on an ice-covered street”. WhiteSpace – one blank could mean 1 while 2 blanks could mean 0 Hiding Grammar – example Texthide. Need to make sure that message structure isn’t changed to much or the sentences become nonsensical Cipher is basically like a rulebook WATERMARKING 1 1

23 REZA MOHAMMADI Text Techniques Dear Friend , Especially for you - this red-hot intelligence. We will comply with all removal requests . This mail is being sent in compliance with Senate bill 2116 , Title 9 ; Section 303 ! THIS IS NOT A GET RICH SCHEME.Why work for somebody else when you can become rich inside 57 weeks . Have you ever noticed most everyone has a cellphone & people love convenience . Well, now is your chance to capitalize on this . WE will help YOU SELL MORE and sell more ! You are guaranteed to succeed because we take all the risk ! But don't believe us . Ms Simpson of Washington tried us and says "My only problem now is where to park all my cars" . This offer is 100% legal . You will blame yourself forever if you don't order now ! Sign up a friend and you'll get a discount of 50% . Thank-you for your serious consideration of our offer . Dear Decision maker ; Thank-you for your interest in our briefing . If you are not interested in our publications and wish to . . . Text being hidden: “I'm having a great time learning about computer security”. WATERMARKING 1 1

24 REZA MOHAMMADI Text Techniques XML Universal format for structured data and documents. Basic technology for information exchange. Due to this security is a growing factor which Steganography can help solve… Different components in which data can be hidden – css, dtd, xsl. WATERMARKING 1 1

25 <img></img> … 0
REZA MOHAMMADI Text Techniques Using tag structure to hide information Stego key: <img></img> … 0 <img/> … 1 Stego data: <img src=”foo1.jpg”></img> <img src=”foo2.jpg”/> <img src=”foo3.jpg”/> <img src=”foo4.jpg”/> <img src=”foo5.jpg”></img> Bit String: 01110 WATERMARKING 1 1

26 Text Techniques Using white space in tags Stego key:
REZA MOHAMMADI Text Techniques Using white space in tags Stego key: <tag>, </tag>, or <tag/> -> 0 <tag >, </tag >, or <tag /> -> 1 Stego data: <user ><name>Alice</name ><id >01</id></user> <user><name >Bob</name><id>02</id ></user > Bit String: Bit String: WATERMARKING 1 1

27 Image Techniques Simple Watermarking
REZA MOHAMMADI Image Techniques Simple Watermarking A simple way of watermarking images is to embed another image into them. This embedded image can be a company logo or name etc. + = WATERMARKING 1 1

28 Image Techniques LSB – Least Significant Bit
REZA MOHAMMADI Image Techniques LSB – Least Significant Bit A simple yet effective way of hiding data in an image for any purpose. The least significant bits of the host image are used to hide the most significant bits of the hidden image (for image-in-image hiding). The least significant bits can always be used to hide other data types. The next example will show how image-in-image hiding works via this method. WATERMARKING 1 1

29 Image Techniques Store host image and hidden image in memory.
REZA MOHAMMADI Image Techniques Store host image and hidden image in memory. Pick the number of bits you wish to hide the hidden image in. Scan through the host image and alter its LSB’s with the hidden images MSB’s. So when 4 bits are used to hide information… Host Pixel: Secret Pixel: New Image Pixel: To extract the hidden image, you basically take out the LSB’s from the host image and create a new image from them. WATERMARKING 1 1

30 Image Techniques Bit Level 7 Bit Level 4 Bit Level 1 Original Images
REZA MOHAMMADI Image Techniques Bit Level 7 Bit Level 4 Bit Level 1 Original Images WATERMARKING 1 1

31 REZA MOHAMMADI Image Techniques This method works best when both the hidden image and host image have equal priority in terms of the number of bits used. Not a very good way of watermarking as it is easy to remove the hidden data. The hidden data can easily be corrupted by noise. The LSB’s can be used to store other information like text – the only limitation is the size of the data you wish to store. WATERMARKING 1 1

32 Image Techniques DCT (Direct Cosine Transformation)
REZA MOHAMMADI Image Techniques DCT (Direct Cosine Transformation) DCT’s convert images from the spatial domain to the frequency domain. High frequencies correspond to rapidly changing pixel values. Low frequencies correspond to slowly changing pixel values. Used to compress JPEG images and can be used as part of a information hiding technique. WATERMARKING 1 1

33 REZA MOHAMMADI Image Techniques A Quantizer is used as part of the JPEG compression technique. It lowers the accuracy of the DCT coefficients which are obtained by executing a DCT on 8x8 blocks of the host image. These values can be tweaked to be all even or all odd. All even = 1 All odd = 0 An image can store 1 bit of information per 8x8 block. First the image is split up into 8x8 squares. Next each of these squares is transformed via a DCT, which outputs a multi dimensional array of 63 coefficients. A quantizer rounds each of these coefficients, which essentially is the compression stage as this is where data is lost. Small unimportant coefficients are rounded to 0 while larger ones lose some of their precision At this stage you should have an array of streamlined coefficients, which are further compressed via a Huffman encoding scheme or similar. Decompression is done via an inverse DCT WATERMARKING 1 1

34 Image Techniques DCT example Original Watermarked REZA MOHAMMADI
Different methods use different ways to encode the hidden data. Can hide pseudo noise Can encode bits via different algorithms on the coefficients These more complex methods generally are better at withstanding attacks Original Watermarked WATERMARKING 1 1

35 Image Techniques Wavelet Transformation
REZA MOHAMMADI Image Techniques Wavelet Transformation Wavelets are mathematical functions for image compression and digital signal processing. Used in the JPEG2000 standard. Wavelets are better for higher compression levels than the DCT method. Generally wavelets are more robust and are a good way of hiding data. WATERMARKING 1 1

36 REZA MOHAMMADI Sound Techniques MP3 The data to be hidden is stored as the MP3 file is created – in the compression stage. As the sound file is being compressed, data is selectively lost depending on the bit rate the user has specified. The hidden data is encoded in the parity bit of this information. To retrieve the data all you need to do is uncompress the MP3 file and read the parity bits. WATERMARKING 1 1

A popular application of watermarking techniques is to provide a proof of ownership of digital data by embedding copyright statements into video or image digital products. Data augmentation - to add information for the benefit of the public. Source tracking (different recipients get differently watermarked content) Broadcast monitoring (television news often contains watermarked video from international agencies) Covert communication All kind of data can be watermarked: audio, images, video, formatted text, 3D models, model animation parameters, … R.MOHAMMADI DIGITAL WATERMARKING

38 Steganography/Watermarking versus Cryptography
The purpose of both is to provide secret communication. Cryptography hides the contents of the message from an attacker, but not the existence of the message. Steganography/watermarking even hide the very existence of the message in the communicating data. Consequently, the concept of breaking the system is different for cryptosystems and stegosystems (watermarking systems). A cryptographic system is broken when the attacker can read the secrete message. Breaking of a steganographic/watermarking system has two stages: - The attacker can detect that steganography/watermarking has been used; - The attacker is able to read, modify or remove the hidden message. R.MOHAMMADI DIGITAL WATERMARKING

39 References “Digital Watermarking Frequently Asked Questions.” april 30, 2008. R.MOHAMMADI DIGITAL WATERMARKING


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