steganography and watermarking

steganography & watermarking by Sudip Nandi

OVERVIEWInformation hiddingSteganography DefinedBlock diagramSteganography in various mediaSteganalysisApplicationAdvantages and DisadvantagesWatermarking

INTRODUCTION

Information Hiding Techniques

Information Hiding

Steganography Watermarking

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Information Hiding Information Hiding : Communication of information by embedding in original data and retrieving it from other digital data. Depending on application we may need process to be imperceptible, robust, secure. Etc.

Where can we hide? Media

Video Audio Still Images Documents

Software Etc. We focus on data hiding in media. We mainly use images but techniques and concepts can be suitably generalized to other media.

Why Hide?

Because you don’t want any one to even know about its existence. Covert communication – Steganography

Because you want to protect it from malicious use. copy protection and deterrence - Digital Watermarks

STEGANOGRAPHY

STEGANOGRAPHY DEFINED

The word steganography comes from the Greek ‘steganos’ , meaning covered or secret, and ‘graphy’ , meaning writing or drawing. Therefore, steganography literally means – “covered writing”.

Block diagram of Steganography

STEGANOGRAPHY UNDER VaRIOUS MEDIA

Steganography in “TEXT”

Steganography in “IMAGES”

Steganography in “AUDIO”

STEGANOGRAPHY IN TEXT

It involves three types of coding:

Line-Shift Coding : Here, text lines are vertically shifted to

encode the document uniquely.

Word-Shift Coding : The codewords are coded into a

document by shifting the horizontal locations of words within

text lines, while maintaining a natural spacing appearance.

STEGANOGRAPHY IN IMAGE

Digital images are made up of pixels. The arrangement of pixels make up the image. Each pixel can have 8-bit(Gray image) and 24-bit(Color image) binary number. The larger the image size, the more

information you can hide. However, larger images may require compression to avoid detection

GRAYSCALE PALETTE

NEBULA PALETTE

IMAGE-BASED TECHNIQUESLeast Significant Bit Insertion : Replaces least significant bits with the message to be encoded A sample raster data for 3 pixels (9 bytes)

00100111 11101001 1100100000100111 11001000 1110100111001000 00100111 11101011

00100110 11101001 1100100000100110 11001000 1110100011001000 00100111 11101011

Inserting the binaryvalue for

A (01000001)

changes 4 bits

STEGANOGRAPHY IN AUDIO

Audio Environments Digital representation

In audio steganography, secret message is embedded into digitized audio signal which result slight altering of binary sequence of the corresponding audio file. There are several methods are available for audio steganography. We are going to have a brief introduction on some of them.

STEGANOGRAPHY IN AUDIO

Methods of Audio Data Hiding

LSB techniques:

Phase coding :

STEGANALYSISHere 2 methods of Steganalysis are looked into :

detecting messages or their transmission

disabling embedded information

RELATION BETWEEN STEGANOGRAPHY AND STEGANALYSIS

APPLICATION OF STEGANOGRAPHY

Confidential communication and secret data storing

Protection of data alteration

Media database system

• ADVANTAGES : Difficult to detect and Only receiver can detect. It can be done faster with large no. of softwares.

DISADVANTAGES : The confidentiality of information is maintained by the algorithms,

and if the algorithms are known then this technique is of no use.

Password leakage may occur and it leads to the unauthorized access of data.

ADVANTAGE AND DISADVANTAGE OF STEGANOGRAPHY

STEGANOGRAPHY VS WATERMARKING

Watermarking is a process in which the information which verifies the owner is embedded into the digital image or signal. These signals could be either videos or pictures or audios;

steganography is changing the image in a way that only the sender and the intended recipient are able to detect the message sent through it.

Watermarking is of two types; visible watermarking and invisible watermarking. Steganography is typically invisible.

The ease in use and abundant availability of steganography tools

has law enforcement concerned in trafficking of illicit material via web

page images, audio, and other transmissions over the Internet. This seminar provides an overview of steganalysis and introduced

some characteristics of steganographic software that point signs of

information hiding.Formerly, just an interest of the military, steganography is now

gaining popularity among the masses.

CONCLUSION

Digital Watermarks

What is a Watermark?

A watermark is a “secret message” that is embedded into a “cover message”. Usually, only the knowledge of a secret key allows us to extract the watermark.

Visible Watermarking Invisible Watermarking

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History• The Italians where the 1st to use watermarks in the

manufacture of paper in the 1270's.

• A watermark was used in banknote production by the Bank of England in 1697.

It is a good security feature because the watermark cannot be photocopied or scanned effectively.

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Why Watermark? Motivation

Copyright protection of multimedia data Copyright owners want to be compensated every time their work is used. The need to limit the number of copies created whereas

the watermarks are modified by the hardware and at some point would not create any more copies (i.e. DVD) - the reading device must be able to modify the watermark

Content protection – content stamped with a visible watermark that is very difficult to remove so that it can be publicly and freely distributed

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Watermarks Classification

1. Paper Watermark: Intended to be somewhat visible.

2. Digital Watermark: A digital signal or pattern imposed on a digital document ( text, graphics, multimedia presentations , …).

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Paper Watermark The technique of impressing into the paper a

form of image or text.

“Cannot be photocopied or scanned effectively”

Purpose: To make forgery more difficult to record the manufacturer’s trademark, Copyright protection, logos, etc …

Used in : Currency, Banknotes , Passports, …

Paper watermarkExample

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Digital Watermarking Types

Visible and Invisible: Visible such as a company logo stamped on an image or

Video. Invisible intended to be imperceptible to the human eye or

inaudible. the watermark can only be determined through watermark extraction or detection by computers.

Visible Watermarking Invisible Watermarking

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Watermarking Process

• Two major steps:

– Location Selection : Where to embed watermark – Processing : How to modify original data to embed

watermark

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Watermarking Embedding & Extraction

Cover Image Cover + WM

Embedding F : Watermarked Image = Function (Cover, Watermark, Key)

Extraction F : Watermark = Function (Watermarked Image, Key(

Cover + WM

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Watermarking Techniques

• Text – Varying spaces after punctuation, spaces in between lines of text, spaces at the end of sentences, etc.

• Audio – Low bit coding, random.

• Images / Video – Least-significant bit, random

It is used for copyright protection.It is used for source tracing.Annotation of photographs.

APPLICATION OF WATERMARKING

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Limitations / Conclusions

• Rapidly growing field of digitized images, video and audio has urged for the need of protection.

• Watermarking is a key process in the protection of copyright ownership of electronic data (image, videos, audio, ...).

• Digital watermarking does not prevent copying or distribution.

• Digital watermarking alone is not a complete solution for access/copy control or copyright protection.

• Digital watermarks cannot survive every possible attack.

REFERENCES

[4] L. Boney, A. Tewfik, and K. Hamdy, “Digital watermarks for audio signals,” in IEEE Proc. Multimedia, 1996, pp. 473-480.

1)Petitcol Fabien A.P., “Information Hiding: Techniques for Steganography and DigitalWatermarking.”, 2000.

2) StegoArchive, “Steganography Information, Software and News to enhance your Privacy”,2001, URL: www.StegoArchive.com3) Petitcolas, Fabien A.P., “The Information Hiding Homepage: Digital Watermarking andSteganography”,URL: http://www.cl.cam.ac.uk/~fapp2/steganography/

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