Fundamentals of Watermarking and Data Hiding

Pierre Moulin

University of Illinois at Urbana–ChampaignDept of Electrical and Computer Engineering

moulin@ifp.uiuc.edu

July 9, 2006 ISIT Tutorial, Seattle

c©2006 by Pierre Moulin. All rights reserved.

1

Outline

1. Overview

2. Basic Techniques

3. Binning Schemes and QIM Codes

4. Performance Analysis: Error Probabilities

5. Performance Analysis: Capacity

6. Applications to Images & Advanced Topics

2

SESSION 1: OVERVIEW

• Data hiding, watermarking, steganography

• Basic properties: fidelity, payload, robustness, security

3

Some Reading

• Books:

Digital Watermarking, by I. Cox, M. Miller, J. Bloom,Morgan-Kaufmann, 2002

Information Hiding Techniques for Steganography and DigitalWatermarking, by S. Katzenbeisser and F. Petitcolas, Eds.,Artech House, 2000

Information Hiding: Steganography and Watermarking,by N. Johnson, Z. Duric and S. Jajodia, Kluwer, 2000

4

• New IEEE Transactions on Information Forensics and Security(quarterly, inaugural issue in March 2006)

• Special issues of various IEEE journals, 1999 – 2005

• Annual Information Hiding Workshops

• Watermarking newsletter: www.watermarkingworld.org

• www.ifp.uiuc.edu/˜moulin

• Tutorial paper “Data Hiding Codes” by P. Moulin andR. Koetter, Proceedings IEEE, December 2005.

5

Multimedia Security

• Dissemination of digital documents

• Owner identification

• Forgery detection

• Identification of illegal copies

• Intellectual protection

6

Authentication

7

8

Media Elements

• Audio

• Images

• Video

• Graphics

• Documents

• Computer programs

9

Nonadversarial Applications

• Database annotation

• Information embedding, e.g., audio in images, text in hostsignals (movie subtitles, financial data, synchronization signals)

10

Data Hiding

• Embed data in covertext (high payload)

• Perceptual similarity requirement

• Multimedia database management

• Covert communications (military, spies, etc.)

• Steganography (στεγανω γραφω, covert writing):conceal existence of hidden message

11

Watermarking

• Hide a few bits of information

• Original and modified signals should be perceptually similar

• Application to digital cameras, TV, DVD video, audio

• Authentication

• Transaction tracking

• Broadcast monitoring

12

Fingerprinting

• Fingerprinter marks several copies of original and distributescopies to users 1, 2, · · · , L

• Each mark is different

• Users may collude to “remove” watermarks

• Applications: copy control, traitor tracing

13

Summary of Applications

Applications

Watermarking authentication, copyright protection

Data hiding covert communications, database annotation,

information embedding

Steganography covert communications

Fingerprinting copy control, traitor tracing

14

A Brief History

• Tattoo hidden message on head of slave (ancient Greeks)

• Invisible ink

• Secret point patterns

• Watermarks in paper (Italy, 13th century)

• Digital watermarking: early 1990’s

• Standardization attempts:SDMI (music), ISO (MPEG video)

15

Hiding Data in Images

secretkey k

Encoderoriginal image S watermarked image X

Picture taken by Alice on January 1, 2000. This messageis going to be embedded foreverin this picture. I challenge youto remove the message withoutsubstantially altering the picture.

1001001101001110100...............101

binary representation

Decoder

Picture taken by Alice on January 1, 2000. This messageis going to be embedded foreverin this picture. I challenge youto remove the message withoutsubstantially altering the picture.

Decoded message

1001001101001110100...............101

Decoded binarymessage

secret key k

Attack

Pirate

11011000...01

16

Decoder’s Task

17

Attacks on Images

Original JPEG, QF=10 4× 4 median filtering

Gaussian filter (σ = 3) Rotated by 10 degrees Random bend

18

Basic Properties

• Fidelity (in terms of signal distortion metric)

• Payload (number of transmitted bits)

• Robustness (against adversary)

• Security (cryptanalysis of randomized code)

• Detectability (by steganalyzers/eavesdroppers)

19

System Issues

• System complexity

• Does decoder know host signal?(public vs private watermarking)

• Security level?

• Reliance on private or public cryptographic system?

20

Attack Models

• No attack

• Deterministic attacks (reversible & irreversible)

• Stochastic attacks (memoryless & stationary)

• Code breaking

• System attacks (e.g., ambiguity, sensitivity & scrambling)

• Benchmarking (e.g., Stirmark)

21

Attacks

Attack Type Examples

Memoryless independent noise,

random pixel replacement

Blockwise memoryless JPEG compression

Attacks with stationary noise,

”statistical regularity” spatially invariant filtering,

some estimation attacks

Deterministic compression, format changes

Arbitrary attacks cropping, permutations,

desynchronization,

nonstationary noise

22

Basic Theoretical Concepts

• Information theory

• Game theory

• Detection and estimation theory

• Coding theory

• Cryptography

23

Purposes of an Information-Theoretic Approach

• make appropriate simplifying assumptions to understandfundamental limits of IH and optimally design algorithms

• provide new insights into IH

• provide a precise framework for evaluating any IH algorithm

• develop approach that generalizes easily to related problems

Caution: cost of mismodeling may be severe in game withopponent!

24