Reza Mohammadi Shiraz University Of Technology R.MOHAMMADIDIGITAL WATERMARKING1 In The Name Of God.

DIGITAL WATERMARKING

Reza Mohammadi

Shiraz University Of Technology

R.MOHAMMADI DIGITAL WATERMARKING 1

In The Name Of God

DIGITAL WATERMARKING 2

Outline

Information Hiding Concept & History Digital Watermarking Digital Watermarking Types Watermarking Algorithm Requirements Digital Watermarking Techniques Digital Watermarking Applications References

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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.

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Stego – Hidden , Graphy – Writing ‘art of hidden writing’


History 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.R.MOHAMMADI

5DIGITAL WATERMARKING

The Need for Data Hiding

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• 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)

Introduction

Steganography(covered writing, covert channels)

Protection against detection

(data hiding)

Protection against removal(document marking)

Watermarking(all objects are marked

in the same way)

Fingerprinting(identify all objects, every

object is marked specific)


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.

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STEGANOGRAPHY versus 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.

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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

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Two Types of Digital Watermarks

A. 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.

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Two Types of Digital Watermarks

B. Invisible watermarksdo 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).

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http://en.wikipedia.org/wiki/Watermark_detection


Invisible Watermark

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Basic Principle in Steganography/Watermarking

Encoder

Decoder

Cover Image

Secret Image

Key

Stego Object

Original Cover

Secret Image Communications

Channel

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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)

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Watermarking Techniques

Binary Files Text

Document XML

Images LSB, DCT, Wavelet

Audio Midi, MP3

Other Types

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; b = 3; b = 3;

b = 3; c = b + 3; a = 2; c = b +3;

c = b + 3; a = 2; c = b + 3; d = b +c;

d = b + c; d = b + c; d = b + c; a = 2;


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.

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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.

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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.

Encoder

Codebook

Original Document Marked Documents


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 01000001, that is 65, the ASCII character code for A.

Shifts lines up slightly up or down

Lines to be shifted decided by CodebookShifted up slightly

h+i

h-i

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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”.

Text Techniques

Text being hidden: “I'm having a great time learning about computer security”.

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 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.

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

Text Techniques Using white space in

tags

Bit String: 101100

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: 010011

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.

+ =

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.

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: 10110001Secret Pixel: 00111111

New Image Pixel: 10110011

To extract the hidden image, you basically take out the LSB’s from the host image and create a new image from them.

Image Techniques

Original ImagesBit Level 1Bit Level 4Bit Level 7

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.

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.

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 = 1All odd = 0

An image can store 1 bit of information per 8x8 block.

Image Techniques

DCT example

Original Watermarked

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.

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.


APPLICATIONS of WATERMARKING 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, …

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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.

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DIGITAL WATERMARKING

References

“Digital Watermarking Frequently Asked Questions.” http://www.watermarkingworld.org/faq.html april 30, 2008.

http://en.wikipedia.org/wiki/Digital_watermark

www.ws.binghamton.edu/fridrich/Research/tutor1.ppt

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http://www.ws.binghamton.edu/fridrich/Research/tutor1.ppt

http://www.ws.binghamton.edu/fridrich/Research/tutor1.ppt


Questions

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Reza Mohammadi Shiraz University Of Technology R.MOHAMMADIDIGITAL WATERMARKING1 In The Name Of God.

Documents

video video

hidden data

main goal of watermarking

data hiding r

digital audio

video cover data d

information hiding

hidden messages