Digital Watermarking for Multimedia Security R. Chandramouli MSyNC:Multimedia Systems, Networking, and Communications Lab Stevens Institute of Technology

Encoding l LSB (Least Significant Bit) Modification l MSB ( Most Significant Bit) Modification Eg : LSB MSB

Example:LSB Encoding Original Image Watermark

Replace 4 and 7 LSBs of Original 4 LSBs Watermarked 7 LSBs Watermarked

What is a Watermark? l A watermark is a “secret message” that is embedded into a “cover (original or host) message”. l Only the knowledge of a secret key allows us to extract the watermark from the cover message. l Effectiveness of a watermarking algorithm is a function of its »Resilience to attacks. »Capacity. »Stealth.

What Can Be Watermarked? l Multimedia data. »Video. »Audio. »Still Images. »Documents. l Software. l Hardware designs.

Multimedia Watermarks l A digital watermark is a “secret key dependent” signal “inserted” into digital multimedia data. l Watermark can be later detected/extracted in order to make an assertion about the data. l A digital watermark can be. »Visible (perceptible). » Invisible (imperceptible).

Watermark Applications l Proof of ownership. »Prove ownership in a court of law. »Simple copyright notice may not help for digital multimedia data. Easily destroyed. l 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. l Content protection (visible watermarks). »Destruction of watermark destroys the content.

Watermark Applications l Authentication. »Detect if image/video has been altered. »Digital cameras. l Media Bridging. »Bridge media such as magazines and the Internet. »Digimarc. l Broadcast Monitoring. »Keep track of when and where an advertisement is played. »ConfirMedia from Verance.

Watermark Applications l Fingerprinting. »Identify the source of an illegal copy. »Unique watermark embedded in each copy. »DiVX, a modified version of DVD. l 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 l 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 Robustness Payload Security

Example: Additive Watermarks I W ( x, y )= I ( x, y )+ k  W ( x, y ) W(x,y) detected No W(x,y) detected

Additive watermarks in transform domain: Spread Spectrum

Watermark Attacks l 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 l Passive Attacks. »Hacker tries to find if a watermark is present. »Removal of watermark is not an aim. »Serious for covert communications. l 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 l 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 l Information Theoretic Issues. »Compute “watermarking capacity” »How many watermark bits can be hidden in a watermark channel ? »Capacity when multiple watermarks are used. l Decision Theoretic Issues. »Robust watermark detector. »Quickest possible watermark detection. »Invariant to statistical uncertainties. »Achieves desired false alarm and detection probabilities.

Watermarking Research l Signal Processing Issues. »What transforms to use ? – wavelet, DCT etc. »Geometric invariant transform – scale, translation, and rotation invariance. l Watermarking protocols and system issues. »Protocol used by sender and receiver for secure transmission. l 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 Demodulation X

Techniques Developed at MSyNC Lab (some results are in collaboration with Iowa State U. and Polytechnic U.)

Information Theoretic Formulation l A new watermark channel model. »Multiplicative and additive attacks. »Models geometric attacks (“killer” attack). l Attack parameters assumed imperfectly known. l Lower and upper bounds on watermarking capacity. l Many current capacity estimates are specific cases of proposed estimates. l Capacity in the presence of multiple watermarks using multiuser information theory.

Multiple Description Watermarking l 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. l Rate-distortion theory formulation.

Decision Theoretic Formulation l How many pixels to watermark ? »A new measure for watermarking capacity. »Different from standard information theoretic formulation. »Perhaps a more practical measure. l Fast watermark detector. »Computation reduction. »Useful for hardware implementation.

Steganalysis l A distributed detection framework for analyzing images for presence of watermarks. l Theoretical formulation and practical algorithm for steganalysis of LSB based image watermarking. l A new watermarking capacity measure called “steganographic capacity”.

Projected Applications of Proposed Techniques l Secure media streaming. l Wireless multimedia security. l Watermark error resilience coding. l Error concealment for wireless multimedia transmission. l Refer to »

Million Dollar Question Watermarking or Encryption or Combination?