digital watermarking for multimedia security r. chandramouli msync:multimedia systems, networking,...

Digital Watermarking for Multimedia Security

R. Chandramouli

MSyNC:Multimedia Systems, Networking, and Communications Lab

Stevens Institute of Technology

Encoding

LSB (Least Significant Bit) Modification MSB ( Most Significant Bit) Modification

Eg : 11010010

LSBMSB

Example:LSB Encoding

Original Image Watermark

Replace 4 and 7 LSBs of Original

4 LSBs Watermarked 7 LSBs Watermarked

What is a Watermark?

A watermark is a “secret message” that is embedded into a “cover (original or host) message”.

Only the knowledge of a secret key allows us to extract the watermark from the cover message.

Effectiveness of a watermarking algorithm is a function of its» Resilience to attacks.» Capacity.» Stealth.

What Can Be Watermarked?

Multimedia data.» Video.» Audio.» Still Images.» Documents.

Software. Hardware designs.

Multimedia Watermarks

A digital watermark is a “secret key dependent” signal “inserted” into digital multimedia data.

Watermark can be later detected/extracted in order to make an assertion about the data.

A digital watermark can be.» Visible (perceptible).» Invisible (imperceptible).

Watermark Applications

Proof of ownership.» Prove ownership in a court of law.» Simple copyright notice may not help for digital

multimedia data. Easily destroyed. Copy prevention or control.

» Recording device may inhibit recording a signal if detected watermark indicates that it is prohibited.

» DVD video and digital music distribution. Content protection (visible watermarks).

» Destruction of watermark destroys the content.

Watermark Applications

Authentication.» Detect if image/video has been altered.» Digital cameras.

Media Bridging.» Bridge media such as magazines and the Internet.» Digimarc.

Broadcast Monitoring.» Keep track of when and where an advertisement is

played.» ConfirMedia from Verance.

Watermark Applications

Fingerprinting.» Identify the source of an illegal copy.» Unique watermark embedded in each copy.» DiVX, a modified version of DVD.

Secret Communications.» Hide information such that general public do not

know its presence.» Bin Laden hides attack plans in images on the

web – USA Today, Feb. 26, 2001.

Requirements

Requirements vary with application. For example:» Perceptually transparent - must not perceptually

degrade original content.» Robust - survive accidental or malicious attempts

at removal.» Oblivious or Non-oblivious - Recoverable with or

without access to original.» Capacity – Number of watermark bits embedded.» Efficient encoding and/or decoding.

Contradicting Requirements

Perceptual Transparency

Oblivious vs. Non-Oblivious

RobustnessPayload Security

Example: Additive Watermarks

W(x,y): Pseudo Random Pattern {-1,0,1}

kMultiply by gain

factork

I(x,y) IW(x,y)

IW(x,y)= I(x,y)+ k W(x,y)

W(x,y) detected T

' ( , ) ( , )WI x y W x yR T

No W(x,y) detected

fh

fv

Additive watermarks in transform domain: Spread

Spectrum

Watermark Attacks

Active Attacks.» Hacker attempts to remove or destroy the

watermark.» Watermark detector unable to detect watermark.» Key issue in proof of ownership, fingerprinting,

copy control.» Not serious for authentication or covert

communication.

Watermark Attacks

Passive Attacks.» Hacker tries to find if a watermark is present.» Removal of watermark is not an aim.» Serious for covert communications.

Collusion Attacks.» Hacker uses several copies of watermarked data

(images, video etc.) to construct a copy with no watermark.

» Uses several copies to find the watermark.» Serious for fingerprinting applications.

Watermark Attacks

Forgery Attacks.» Hacker tries to embed a valid watermark.» Serious in authentication.» If hacker embeds a valid authentication

watermark, watermark detector can accept bogus or modified media.

Example: Forging Photo I.D.

Bad Forgery!

Millionaire with Swiss bank

account

Assistant Professor

Thanks

Hong Man, for this picture!

Content-based Watermarking

Original Watermark

JPEG Compression Attack

Watermarking Research

Information Theoretic Issues.» Compute “watermarking capacity”» How many watermark bits can be hidden in a

watermark channel ?» Capacity when multiple watermarks are used.

Decision Theoretic Issues.» Robust watermark detector.» Quickest possible watermark detection.» Invariant to statistical uncertainties.» Achieves desired false alarm and detection

probabilities.

Watermarking Research Signal Processing Issues.

» What transforms to use ? – wavelet, DCT etc.» Geometric invariant transform – scale, translation, and

rotation invariance. Watermarking protocols and system issues.

» Protocol used by sender and receiver for secure transmission.

Steganalysis.» How to analyze multimedia data for the presence of

watermark(s).» Secure Digital Music Initiative (SDMI) has been hacked!

Robust Watermarking Techniques - A

Communications Framework

+

Media Carrier

HVS

Watermark

Media Carrier

Noise/Attack Channel

Water-

mark

Coding and

Modulation

Decoding and

DemodulationX

Techniques Developed at MSyNC Lab

(some results are in collaboration with Iowa State U. and Polytechnic U.)

Information Theoretic Formulation

A new watermark channel model.» Multiplicative and additive attacks.» Models geometric attacks (“killer” attack).

Attack parameters assumed imperfectly known. Lower and upper bounds on watermarking

capacity. Many current capacity estimates are specific

cases of proposed estimates. Capacity in the presence of multiple

watermarks using multiuser information theory.

Multiple Description Watermarking

A new framework for watermarking using multiple description codes.» Partition the source into multiple descriptions.» Each description carries enough information.» Allocate watermarking bits to descriptions subject

to distortion constraints.» Experiments for secure wireless media

transmission is promising.

Rate-distortion theory formulation.

Decision Theoretic Formulation

How many pixels to watermark ?» A new measure for watermarking capacity.» Different from standard information theoretic

formulation.» Perhaps a more practical measure.

Fast watermark detector.» Computation reduction.» Useful for hardware implementation.

Steganalysis

A distributed detection framework for analyzing images for presence of watermarks.

Theoretical formulation and practical algorithm for steganalysis of LSB based image watermarking.

A new watermarking capacity measure called “steganographic capacity”.

Projected Applications of Proposed Techniques

Secure media streaming. Wireless multimedia security. Watermark error resilience coding. Error concealment for wireless multimedia

transmission. Refer to

» http://www.ece.stevens-tech.edu/~mouli/msync/index.html

Million Dollar Question

Watermarking or Encryption or Combination?