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