Outline Introduction to Data Hiding Watermarking Definition and History Applications Basic Principles Requirements Attacks Evaluation and Benchmarking Examples Steganography Definition and History Applications Basic Principles Examples of Techniques Demos
Data Hiding Information Hiding is a general term encompassing many sub- disciplines Two important sub-disciplines are: Steganography and Watermarking Steganography: Hiding: keeping the existence of the information secret Watermarking Hiding: making the information imperceptible Information hiding is different than cryptography (cryptography is about protecting the content of messages) Secret message Embedding algorithm Carrier document Transmission via network Detector Secret message Key
The Need for Data Hiding Covert communication using images (secret message is hidden in a carrier image) Ownership of digital images, authentication, copyright Data integrity, fraud detection, self-correcting images Traitor-tracing (fingerprinting video-tapes) Adding captions to images, additional information, such as subtitles, to video, embedding subtitles or audio tracks to video (video-in-video) Intelligent browsers, automatic copyright information, viewing a movie in a given rated version Copy control (secondary protection for DVD)
Issues in Data Hiding Perceptibility: does embedding information distort cover medium to a visually unacceptable level (subjective) Capacity: how much information can be hidden relative to its perceptibility (information theory) Robustness to attacks: can embedded data survive manipulation of the stego medium in an effort to destroy, remove, or change the embedded data Trade-offs between the three: More robust => lower capacity Lower perceptibility => lower capacityetc.
Covert communication Copyright protection of images (authentication) Fingerprinting (traitor-tracing) Adding captions to images, additional information, such as subtitles, to videos Image integrity protection (fraud detection) Copy control in DVD Intelligent browsers, automatic copyright information, viewing movies in given rated version Requirements LowHigh capacity robustness invisibility security embedding complexity detection complexity Requirements Application
Security Robustness Capacity The Magic Triangle There is a trade-off between capacity, invisibility, and robustness Secure steganographic techniques Digital watermarking Complexity of embedding / extraction Undetectability Additional factors: Nave steganography
make data hiding possible 2 gray levels 5 gray levels 31 gray levels Original + + + = = = and Information-theoretic Removed by lossless compression Perceptual Removed by lossy compression
Watermarking Intent: data embedding conveys some information about the cover medium such as owner, copyright, or other information Watermark can be considered to be an extended attribute of the data Robustness of watermark is a main issue Know watermark may be there Can be visible or invisible
Steganography Intent: transmit secret message hidden in innocuous-looking cover medium so that its existence is undetectable Robustness not typically an issue Capacity desired for message is large Always invisible Typically dependent on file format
Watermarking:Definition Watermarking is the practice of imperceptibly altering a cover to embed a message about that cover Watermarking is closely related to steganography but, there are differences between the two In watermarking the message is related to the cover Steganography typically relates to covert point-to-point communication between two parties.Therefore, steganography requires only limited robustness Watermarking is often used whenever the cover is available to parties who know the existence of the hidden data and may have an interest in removing it Therefore, watermarking has the additional notion resilience against attempts to remove the hidden data Watermarks are inseparable from the cover in which they are embedded. Unlike cryptography, watermarks can protect content even after they are decoded.
Watermarking:History More than 700 years ago, watermarks were used in Italy indicate the paper brand and the mill that produced it By the 18th century watermarks began to be used as anti- counterfeiting measures on money and other documents The term watermark was introduced near the end of the century.It was probably given because the marks resemble the effects of water on paper The first example of a technology similar to digital watermarking is a patent filed in 1954 by Emil Hembrooke for identifying works In 1988, Komatsu and Tominaga appear to be the first to use the term "digital watermarking" About 1995, interest in digital watermarking began to mushroom
Motivation The rapid revolution in digital multimedia and the ease of generating identical and unauthorized digital data. USA Today, Jan. 2000:Estimated lost revenue from digital audio piracy US $8,500,000,000.00 The need to establish reliable methods for copyright protection and authentication. The need to establish secure invisible channels for covert communications. Adding caption and other additional information.
Watermarking:Applications Copyright protection Most prominent application Embed information about the owner to prevent others from claiming copyright Require very high level of robustness Copy protection Embed watermark to disallow unauthorized copying of the cover For example, a compliant DVD player will not playback or data that carry a "copy never" watermark Content Authentication Embed a watermark to detect modifications to the cover The watermark in this case has low robustness, "fragile"
Watermarking: Requirements Imperceptibility The modifications caused by watermark embedding should be below the perceptible threshold Robustness - The ability of the watermark to resist distortion introduced by standard or malicious data processing Security - A watermark is secure if knowing the algorithms for embedding and extracting does not help unauthorized party to detect or remove the watermark
Digital Watermarking - Examples Text varying spaces after punctuation, spaces in between lines of text, spaces at the end of sentences, etc. Audio low bit coding, random imperceptible noise, fragile & robust, etc. Images least-significant bit, random noise, masking and filtering, etc.
Digital Watermarking Qualities/Types Effect on quality of original content how does watermarking technique impact level of degradation and what is the level of acceptability with the degradation Visible vs. invisible visible such as a company logo stamped on an image or movie or invisible and imperceptible Fragile vs. robust fragile watermarks break down easily whereas robust survive manipulations of content (in some watermarking of audio files, both are used)
Digital Watermarking Qualities/Types. Public vs. private private watermarking techniques require that the original be used as a basis of encryption whereas public does not Public-key vs. secret-key secret-key watermarking uses the same watermarking key to read the content as the key that was inserted into the image; public key uses different keys for watermarking the image and reading the image
Digital watermarks categories Robust watermark- Used for copyright protection. Requirements: the watermark should be permanently intact to the host signal, removing the watermark result in destroying the perceptual quality of the signal. Fragile watermark- Used for tamper detection or as a digital signature. Requirements: Break very easily under any modification of the host signal. Semi Fragile watermark- used for data authentication. Requirements: Robust to some benign modifications, but brake very easily to other attacks. Provide information about the location and nature of attack
Copyright protection of digital images (authentication) Original += WatermarkWatermarked image Robustness against all kinds of image distortion Robustness to intentional removal even when all details about the watermarking scheme are known (Kerckhoffs principle) Watermark pattern must be perceptually transparent Watermark depends on a secret key Robustness to over-watermarking, collusion, and other attacks
Ownership is proved by showing that an image in question contains a watermark that depends on owners secret key If pirate embeds his own watermark, the ownership can be resolved by producing the original image or the watermarked image (neither contains pirates watermark) Detectable watermark: Pseudo-random sequence is either present or not present (1 bit embedded) Readable watermark: One can recover a short message, e.g. info about the owner (100 bits) Proving ownership using a digital watermark
Robust, secure, invisible watermark, resistant with respect to the collusion attack (averaging copies of documents with different marks). Fingerprintin
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