Steganography and Watermarking

Steganography and Watermarking
CSCI284 Spring 2004 GWU

CS284/Spring04/GWU/Vora/RSA
Various Logistics Project presentations on: 26th April, Monday, 6:10-7:40 27th April, Tuesday, 6:10-7:40 (make-up day) and 28th April, Wednesday, 6:10-7:40 (another make-up day) 11/7/2018 CS284/Spring04/GWU/Vora/RSA

What is steganography? Hide not just the message, but also the existence of the message. Steganographic message in another message Outer message (“carrier”) can be: text, image, audio, video, binary 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Text Steganography Minor details about format encode the message: Margins Space between lines, paras, words Infra-red or other non-perceptible marks Can be broken without knowing the specific minor details, by intentionally changing margins, space between lines, paras, words, etc. Infra-red marks can be detected by putting through infra-red detection 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Media Steganography For secret messages and copyright protection Reqt: message should remain undetected and/or in the media after transformations that do not “degrade” the carrier. What is meant by “degrade”? Unanswered. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Definitions Imperceptible digital watermark Information inserted in a digital media asset (text, audio, video, image, typically denoted as a `signal') so that it is not detectable by the human perceptual systems. 2. Robust watermark 2a. Most ambitious statement A watermark that can be removed only by degrading the perceptual quality of the signal. (i.e., if the signal retains perceptual quality, watermark is detectable and/or readable). Not solved - far from being solved. Issues with problem statement include: definition of perceptible, perceptual quality - formulae/models do not exist. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Definitions 2b. Less ambitious statement A watermark that is retained by a finite set of transformations that do not alter the perceptual quality of a signal (for example, printing and rescanning only; colour transformations only; filtering only: sharpening, blurring; geometric transformations only). Sometimes called semi-fragile watermarking. Reasonably well-solved. Useful in copyright protection when all attempts to change signal are honest, i.e. not to remove watermark, or system is closed, and signal is accessible only on low computation device. Note: Robust watermark usually imperceptible because if it is perceptible, an attacker can detect where it is and removing is easier. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Definitions 3. Copyright protection using robust watermarking Detecting the presence of a robust watermark in assets suspected to be infringing copyright. Problems: Does not typically prevent copyright infringement, though hypothetically can if watermark detectors in everything used to get to signal. Probably easier to use a recognition or similar algorithm to find similar assets and then claim copyright. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Application: Robust, imperceptible watermarking Prevention of digital media piracy
Physical media piracy Quality deterioration with each copy Distribution visible and expensive, legal enforcement easier Digital media piracy Perfect copies Distribution unsupervised; no clear laws; no means of enforcing them, most important no easy way of locating distribution centers Current OS and digital copies: Any object that needs a PC for viewing can be copied perfectly through file copies, and imperfectly through screen captures 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Multimedia Copyright Protection
Widespread, cheap, Internet access requires a means of copyright protection. Is this image being used the way the buyer promised the seller it would be used? Has it been copied illegitimately? Has the owner been provided adequate compensation for the kind of use (no of copies, resale)? Used in commercial scenarios for sale/resale/distribution 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Copyright protection with a robust, invisible watermark
Owner looks for the watermark - either all over the Internet, or on an individual picture that she suspects was stolen from her. Original picture to be sold on the Internet contains an invisible mark: If she finds it with/being sold by an unauthorized person, she could seek legal recourse. `watermark’ - something that identifies owner or copyright owner All existing methods can be busted by free software available on the Internet; it is not a preventive measure, it merely aids in finding the culprit after the fact; 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Watermark should survive accidental attacks
Original, legal, buyer performs operations on image - sharpening, brightness/colour adjustment, filtering, cropping, resizing, rotation - while retaining perceptual quality of image. Watermark should survive such operations - called accidental attacks - and should remain invisible; ie.e watermark should be robust 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Image quality degrades if watermark removed (intentional attack)
Illegal reseller trys to destroy watermark before reselling. Watermark should damage perceptual quality of image when being removed (detection procedure does not detect the existence of a watermark) or sufficiently altered (the information contained in it is altered sufficiently - identity of owner is changed). Intentional attack. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Problem Statement Copyright protection by insertion of an imperceptible mark in digital media that is robust to intentional and accidental attacks/transformations which preserve the quality of the media Not clear if the above goal is achievable Achievement of the goal requires at least a good understanding of : Models of quality Models of (in)visibility Models of accidental attacks Models of intentional attacks The amount/nature of information that needs to be hidden At present, all of the above are not understood well enough. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

The Problem- contd. The problem involves looking at the trade-offs between: information content and invisibility robustness and invisibility information content and robustness The requirement of robustness to intentional attacks also requires hiding the information so that an attacker cannot find it - or, if she knows where to look, to hide it so that getting rid of it requires image degradation. The problem has been posed in the communications framework as the transmission and detection/estimation of a small signal (the watermark) in a noisy channel (the image). 11/7/2018 CS284/Spring04/GWU/Vora/RSA

A communications channel model
Small amplitude signal §(signature) = W(α, β), the watermark Original image: I(α, β) + W(α, β) = Î (α, β) Marked image Π(Î (α, β)) + noise Transformed image Ð(Π(Î (α, β)) + noise) ? Signature transmitted signal carrier transmitted signal corrupted by channel distortion and additive noise Detection 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Traditional Signal Transmission Methods
AM (Amplitude Modulation) T(t) = (1 + s(t) ) cos(wt + ) FM (Frequency Modulation) T(t) = cos((w + s(t) )dt + ) signal carrier 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Prior Art All except one are additive (or linear) methods - a watermark is added to the image in some domain. The one that is not performs `amplitude modulation’ by multiplying each pixel by a number slightly larger or smaller than unity. In some constraint-based methods, (Pitas et al, Koch et al) the watermark is in the form of constraints on the image coefficients in some domain. Some coefficients satisfy a set of linear equations whose coefficents form the watermark. Enforcing the constraints on the coefficients in the watermarked image is done by addition. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Prior Art - (contd.) Space-Domain-Based Methods - where operations to the image are done in the spatial domain. Easier to implement; white noise nature of added watermark necessary for invisibility. Frequency-(usually DCT)-Domain-Based Methods - operations done in the Fourier domain. White noise nature of mark not as necessary. The newer methods (most notably the NEC-Princeton method due to Cox et al) embed the watermark in the most perceptual regions of the image - the argument is that watermark removal will destroy image quality. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Main Issues Kalker et al, Phillips Research labs., Eindhoven, have shown that all method whose detection is linear can be busted by someone with access to a detector. No existing methods are reasonably robust to geometric transformations (cropping, rotation, scaling). Perhaps nonlinear methods that are based on the image skeleton and other such attributes could be more successful; but the main issue is that the problem is not well-defined enough. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Problems with model for copyright protection
Even if a perfect robust watermarking technique were found, one would need to look for the watermark in every relevant file on the Internet often enough to detect violations. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Uses of robust watermarking
Robust watermarking can possibly be used as a deterrent, but it is not clear if it is worth the investment - time will tell. It could perhaps be used in closed systems that allowed only certain kinds of operations - those that preserve the watermark. These ideas are not well-formulated in the industry or in academia yet. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Step back a little The problem is that current viewers of multimedia (PCs, mostly) also allow other operations on the media. Can we somehow do viewing without allowing other operations? Secure hardware/software viewers - but the operating system still allows copies and screen captures 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Problems with robust watermarking
Watermark must be imperceptible Changes that affect the imperceptible watermark substantially should damage the perceptual quality of image It appears difficult at best to achieve both together. No existing methods do for a large enough amount of hidden information. There are Internet sites that bust every watermarking method. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

aCd9Tof3trefgu Evariste Galois aCd9Tof3trefgu Evariste Galois
Encapsulated Content: Better Security, More Expensive – Prevents Unauthorized Use Content encrypted during transmission and in storage on buyer’s local disk User without decryption sees garbage aCd9Tof3trefgu Evariste Galois aCd9Tof3trefgu Content decrypted in hardware or software to allow viewing and manipulation. Pay per view possible Evariste Galois 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Classification of Rights Management Systems
Complexity of access specifications Low Medium High Personal Family Multimedia Archives Personal publishing using templates Personal metadata? Lessons/hw by students and teachers Mixed Wedding videos professionally filmed Aggregated Personal metadata? Type of Content (Read only) Entertainment Magazine subscriptions Commercial Photography Publishing Press Ebooks Scientific publishing Commercial Use password protection Use secure encapsulation Use secure encapsulation + watermarking 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Major IP holders InterTrust – well-patented encapsulation and asset economy material. Just settled with Microsoft. Xerox subsidiary ContentGuard (with Microsoft investment) - well-patented rights management language technology. IBM – well-patented smaller collection of secure encapsulation technology. Partners with Xerox. Digimarc – well-patented watermarking technology. They are part of an international group of banks, which is considering their technology for counterfeit deterral. Planning to use watermarking as a non-secure data transmission tool across media boundaries. HP: Owns patent on the idea of any kind of watermaking, Morris. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

11/7/2018 CS284/Spring04/GWU/Vora/RSA

Another problem: Authentication of digital media given cheap access to capable processing systems Was this image changed in any way after it was captured? 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Authentication with a fragile, invisible watermark
In a court of law, a judge checks the watermark hidden in the presented image to see if it is associated in the same way with each pixel of the image presented as evidence Original picture contains an invisible mark inserted at `source’: If she finds that the hidden watermark is not what it should be for the presented image, the presented image is not authentic and has been changed since it was obtained. `watermark’ - something that is associated with the value of each pixel of the image 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Definitions 4. Fragile watermark 4a. Most ambitious statement A watermark that indicates any perceptual changes to the signal Unsolved. Issues with problem statement include: definition of perceptible, perceptual quality - formulae/models do not exist. 4b. More ambitious statements A watermark that indicates any change in the image except certain, finite set of transformations that are also known to (somewhat) maintain perceptual quality. Sometimes called semi-fragile watermarking. Solved in some versions. A watermark that indicates any change in the signal while localizing the change. Solved after a few false starts 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Definitions 4c. Least ambitious statement A watermark that indicates any change to signal. Very well-solved using digital signatures that have been around a long time and are more well-tested and far better understood than any watermarking method. 5. Authentication using fragile watermarking Check watermark to see if signal has changed Issues: Do not need watermark for a digital asset, can store information in header. Need watermark only for non-digital assets, but it needs to survive D2A2D and be fragile to everything else. 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Summary Copyright protection watermarking problem: Not well-defined Not solved Thought to be inconsistency in problem definition Not efficient Image authentication: requires closed, trusted system These results are relevant to steg in general, which did not have commercially viable applications before this (might still not have) 11/7/2018 CS284/Spring04/GWU/Vora/RSA

Steganography and Watermarking

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