WatermarkingWatermarking

• University of Palestine• Eng. Wisam Zaqoot• May 2010

Data HidingData Hiding

Information Hiding is a general term encompassing many Information Hiding is a general term encompassing many sub-disciplinessub-disciplines

Two important sub-disciplines are: Two important sub-disciplines are:

Steganography and WatermarkingSteganography and Watermarking Steganography:Steganography:

Hiding: keeping the existence of the information secret Hiding: keeping the existence of the information secret WatermarkingWatermarking

Hiding: making the information imperceptibleHiding: making the information imperceptible

Information hiding is different than cryptography Information hiding is different than cryptography (cryptography is about protecting the content of(cryptography is about protecting the content of messages)messages)

Secretmessage

Embeddingalgorithm

Carrierdocument

Transmissionvia network

Detector

Secretmessage

Key

Key

Why do we need Data Hiding?Why do we need Data Hiding? Covert communication using images (secret Covert communication using images (secret

message is hidden in a carrier image)message is hidden in a carrier image) Ownership of digital images, authentication, Ownership of digital images, authentication,

copyrightcopyright Data integrity, fraud detection, self-correcting Data integrity, fraud detection, self-correcting

imagesimages Traitor-tracing (fingerprinting video-tapes)Traitor-tracing (fingerprinting video-tapes) Adding captions to images, additional Adding captions to images, additional

information, such as subtitles, to video, information, such as subtitles, to video, embedding subtitles or embedding subtitles or

audio tracks to video (video-in-video)audio tracks to video (video-in-video) Copy control (secondary protection for DVD)Copy control (secondary protection for DVD)

Issues in Data HidingIssues in Data Hiding

PerceptibilityPerceptibility: does embedding information : does embedding information “distort” cover medium to a visually “distort” cover medium to a visually unacceptable level (subjective)unacceptable level (subjective)

CapacityCapacity: how much information can be : how much information can be hidden relative to its perceptibility hidden relative to its perceptibility (information theory)(information theory)

Robustness to attacksRobustness to attacks: can embedded data : can embedded data survive manipulation of the stego medium in survive manipulation of the stego medium in an effort to destroy, remove, or change the an effort to destroy, remove, or change the embedded dataembedded data

Trade-offs between the previous threeTrade-offs between the previous three:: More robust => lower capacityMore robust => lower capacity Lower perceptibility => lower capacityLower perceptibility => lower capacity etc.etc.

Security Robustness

Capacity

The “Magic” TriangleThe “Magic” Triangle

There is a trade-offbetween capacity,invisibility, and robustness

Secure steganographictechniques

Digital watermarking

• Complexity of embedding / extraction• Undetectability

Additional factors:

Naïve steganography

WatermarkingWatermarking IntentIntent: data embedding conveys some : data embedding conveys some

information information about the cover mediumabout the cover medium such as owner, copyright, or other such as owner, copyright, or other informationinformation

Watermark can be considered to be an Watermark can be considered to be an extended attribute of the dataextended attribute of the data

Robustness Robustness of watermark is a main issueof watermark is a main issue In some cases, you know watermark may In some cases, you know watermark may

be therebe there Can be Can be visible or invisiblevisible or invisible

Watermarking:Watermarking:DDefinitionefinition

Watermarking is the practice of imperceptibly Watermarking is the practice of imperceptibly altering a cover to embed a message about that altering a cover to embed a message about that covercover

Watermarking is closely related to steganography but, there Watermarking is closely related to steganography but, there are differences between the twoare differences between the two In watermarking the message is related to the cover In watermarking the message is related to the cover Steganography typically relates to covert point-to-point Steganography typically relates to covert point-to-point

communication between two parties. Therefore, communication between two parties. Therefore, steganography requires only limited robustness steganography requires only limited robustness

Watermarking is often used whenever the cover is Watermarking is often used whenever the cover is available to parties who know the existence of the hidden available to parties who know the existence of the hidden data and may have an interest in removing it data and may have an interest in removing it

Therefore, watermarking has the additional notion Therefore, watermarking has the additional notion resilience against attempts to remove the hidden data resilience against attempts to remove the hidden data

Watermarks are inseparable from the cover in which they are Watermarks are inseparable from the cover in which they are embedded. Unlike cryptography, watermarks can protect embedded. Unlike cryptography, watermarks can protect content even after they are decoded.content even after they are decoded.

Watermarking:Watermarking:HistoryHistory More than 700 years ago, watermarks were used in Italy More than 700 years ago, watermarks were used in Italy

indicate the paper brand and the mill that produced it indicate the paper brand and the mill that produced it By the 18th century watermarks began to be used as anti-By the 18th century watermarks began to be used as anti-

counterfeiting measures on money and other documents counterfeiting measures on money and other documents The term watermark was introduced near the end of the The term watermark was introduced near the end of the

century. It was probably given because the marks resemble century. It was probably given because the marks resemble the effects of water on paper the effects of water on paper

The first example of a technology similar to digital The first example of a technology similar to digital watermarking is a patent filed in 1954 by Emil Hembrooke watermarking is a patent filed in 1954 by Emil Hembrooke for identifying worksfor identifying works

In 1988, Komatsu and Tominaga appear to be the first to In 1988, Komatsu and Tominaga appear to be the first to use the term "digital watermarking" use the term "digital watermarking"

About 1995, interest in digital watermarking began to About 1995, interest in digital watermarking began to mushroommushroom

Watermarking Watermarking MotivationsMotivations

• The need to establish reliable methods for The need to establish reliable methods for copyright protection and authentication.copyright protection and authentication.

• The need to establish secure invisible channels for The need to establish secure invisible channels for covert communications.covert communications.

• Adding caption and other additional information. Adding caption and other additional information.

Watermarking:ApplicationsWatermarking:Applications Copyright protection Copyright protection

Most prominent application Most prominent application Embed information about the owner to prevent others Embed information about the owner to prevent others

from claimingfrom claiming copyright copyright Require very high level of robustness Require very high level of robustness

Copy protection Copy protection Embed watermark to disallow unauthorized copying of the Embed watermark to disallow unauthorized copying of the

cover cover For example, a compliant DVD player will not playback For example, a compliant DVD player will not playback

data that carry a "copy never" watermark data that carry a "copy never" watermark Content Authentication Content Authentication

Embed a watermark to detect modifications to the cover Embed a watermark to detect modifications to the cover The watermark in this case has low robustness, "fragile"The watermark in this case has low robustness, "fragile"

Watermarking:Basic Watermarking:Basic principlesprinciples

Watermarking: Watermarking: RequirementsRequirements

Imperceptibility Imperceptibility The modifications caused by watermark embedding should The modifications caused by watermark embedding should

be below the perceptible threshold be below the perceptible threshold Robustness Robustness

The ability of the watermark to resist distortion introduced The ability of the watermark to resist distortion introduced by standard or malicious data processing by standard or malicious data processing

Security Security A watermark is secure if knowing the algorithms for A watermark is secure if knowing the algorithms for

embedding and extracting does not help unauthorized embedding and extracting does not help unauthorized party to detect or remove the watermarkparty to detect or remove the watermark

Digital Watermarking - ExamplesDigital Watermarking - Examples

Text – varying spaces after punctuation, Text – varying spaces after punctuation, spaces in between lines of text, spaces at spaces in between lines of text, spaces at the end of sentences, etc.the end of sentences, etc.

Audio – low bit coding, random Audio – low bit coding, random imperceptible noise, fragile & robust, etc.imperceptible noise, fragile & robust, etc.

Images – least-significant bit, Images – least-significant bit, random noise, masking and filtering, etc.random noise, masking and filtering, etc.

Digital Watermarking – Digital Watermarking – Qualities/TypesQualities/Types

Effect on quality of original content – how does Effect on quality of original content – how does watermarking technique impact level of watermarking technique impact level of degradation and what is the level of degradation and what is the level of acceptability with the degradationacceptability with the degradation

Visible vs. invisible – visible such as a company Visible vs. invisible – visible such as a company logo stamped on an image or movie or invisible logo stamped on an image or movie or invisible and imperceptibleand imperceptible

Fragile vs. robust – fragile watermarks break Fragile vs. robust – fragile watermarks break down easily whereas robust survive down easily whereas robust survive manipulations of content (in some watermarking manipulations of content (in some watermarking of audio files, both are usedof audio files, both are used)

Digital Watermarking –Qualities/Types.Digital Watermarking –Qualities/Types.

Public vs. private – private watermarking Public vs. private – private watermarking techniques require that the original be techniques require that the original be used as a basis of encryption whereas used as a basis of encryption whereas public does notpublic does not

Public-key vs. secret-key – secret-key Public-key vs. secret-key – secret-key watermarking uses the same watermarking watermarking uses the same watermarking key to read the content as the key that key to read the content as the key that was inserted into the image; public key was inserted into the image; public key uses different keys for watermarking the uses different keys for watermarking the image and reading the imageimage and reading the image

Digital watermarks Digital watermarks categoriescategories

Robust watermark-Robust watermark- Used for copyright protection. Used for copyright protection.

Requirements:Requirements: the watermark should be permanently the watermark should be permanently intact to the host signal, removing the watermark result intact to the host signal, removing the watermark result in destroying the perceptual quality of the signal. in destroying the perceptual quality of the signal.

Fragile watermark-Fragile watermark- Used for tamper detection or as a Used for tamper detection or as a digital signature.digital signature.

Requirements:Requirements: Break very easily under any modification of Break very easily under any modification of the host signal.the host signal.

Semi Fragile watermark- Semi Fragile watermark- used for data authentication.used for data authentication.

Requirements:Requirements: Robust to some benign modifications, but Robust to some benign modifications, but brake very easily to other attacks.brake very easily to other attacks.

Provide information about the location and nature of attackProvide information about the location and nature of attack

AttacksAttacks

Attacks are carried out with an intension to Attacks are carried out with an intension to destroy watermark for the purposes of use destroy watermark for the purposes of use without having to pay royalties to the originator without having to pay royalties to the originator of the content.of the content.

Must withstand various signal processing attacks:Must withstand various signal processing attacks: CompressionCompression Cropping, editing, composing.Cropping, editing, composing. Printing.Printing. Adding small amounts of noise.Adding small amounts of noise.