must refer watermarking lecture 1

7/29/2019 Must Refer Watermarking Lecture 1

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Watermarking in E-commerceSystems



Outline

• Introduction, Applications

• Characteristics and classification

• Popular techniques for watermarking

• Attacks on watermarks



History

Paper Watermarks: Formed during the

manufacturing process of the paper when the paper is wet, so that fibers can be disturbed

according to the design of the watermark.

Used mainly for identification andauthentication



Common Examples

• Currency Notes

• Stamps• Passports

• Legal Documents

• Logos used by cable TV channels



Digital Watermarking

Definition: A digital watermark is a

digital signal or pattern inserted into a

digital document such as text, graphicsor multimedia, and carries information

unique to the copyright owner, the

creator of the document or theauthorized consumer.



Example



Watermarking Vs Encryption

• Encryption involves document transformation sothat the contents of the document are not visiblewithout a decryption key

• Watermarking leaves the original file/image intactand recognizable



Watermarking Process



Digital Watermarking Applications

• Ownership Assertion– ‘A’ uses a private key to generate a watermark and embeds it in

the document– ‘A’ makes the watermarked image publicly available – ‘B’ claims that he owns the image derived from the public image – ‘A’ produces the unmarked original and establishes the presence

of ‘A’s watermark

• Fingerprinting

– Used to avoid unauthorized duplication and distribution.– A distinct watermark (a fingerprint) is embedded in each copy

of the data.– If unauthorized copies are found, the origin of the copy can be

determined by retrieving the fingerprint.



Digital Watermarking Applications (2)

• Authentication & integrity verification– Watermarks should be able to detect even the slightest

change in the document.

– A unique key associated with the source is used thecreate the watermark and then embed in the document.

– This key is then used to extract the watermark and theintegrity of the document verified on the basis of theintegrity of the watermark.




• Content labeling– Bits embedded in the data, comprise an annotation, giving

some more information about the data.

– Digital cameras annotate images with the time and date,when the photograph was taken.

– Medical imaging machines annotate images (X-Rays) withpatients name, ID.




• Usage control & Copy protection– Digital watermark inserted to indicate the number of

copies permitted.

– Every time a copy is made the hardware modifies thewatermark and at the same time it would not create anymore copies of the data.

– Commonly used in DVD technology.

• Content Protection

– Content owner might want to publicly and freely provide apreview of multimedia content being sold.– To make the preview commercially useless, content is

stamped with visible watermarks.



Characteristics of Digital Watermarks

• Unobtrusive: invisible enough not to degrade the data quality and toprevent an attacker from finding and deleting it.

• Readily Detectable: the data owner or an independent controlauthority should easily detect it.

• Unambiguous: retrieval of it should unambiguously identify the dataowner.

• Innumerable: it should be possible to generate a largenumber of watermarks, all distinguishable.

• Robust: difficult to remove for an attacker, who would like

to destroy it in order to counterfeit the copyright of thedata. Moreover, removal of it should cause a considerabledegradation in the quality of the data.

• Visible watermarks should be visible enough to discouragetheft.



Digital Watermark Classification

• Based on visibility of watermarks

- Visible Watermarks

- Invisible Watermarks

• Based on the content to be watermarked

- Text Watermarking

- Image, Audio, Video Watermarking



Techniques for Texts

Text Line Coding: Change the spacing

between lines.

Word-shift Coding: Change the spacing

between words.

Character Encoding: Alter the shapes of characters.



Text line coding example



Word-shift coding example



Easily defeated…

• Retyping the text destroys the watermark

• Word processors change the spacing between

words and lines• Character encoding can be defeated by changing

the font



Techniques for Images

• Spatial Watermarking: Just change some of the values ofthe pixels in the lower bit plane; e.g., Change some of thebits from 1 to 0 or 0 to 1.

• Frequency Domain Watermarking: First convert the image tothe frequency domain and then apply the watermark in thelow frequency regions.



Checksum Technique for images

• Watermark is formed from the 7 most significant bits ofeach pixel.

• Eight 7-bit segments (from eight different pixels) are

concatenated and the final checksum is thus 56-bit.• Locations of the pixels that are to contain one bit each of

the checksum are randomly chosen.

• These pixel locations along with the checksum form thewatermark, W.

• Last bit of each pixel is then changed to the correspondingchecksum bit.



Example



Bavarian couple

Original Watermarked Version



Advantages/Disadvantages

• Embedding the checksum only changes (on average) half thenumber of pixel. So less visual distortion.

• Can hold multiple watermarks as long as they don’t overlap.

• Extremely simple and fast.• Extremely fragile. Any change to the checksum causes the

failure of the verification procedure.

• Forger could replace a section with another one of equal sizeand checksum.

• Entire watermark can be removed by removing the LSBplane. Can’t survive lossy compression.



Attacks on CopyrightMarking Systems



Watermarking Attack

• Iterative progress– Attacks will lead to more robust systems

• Various attacks on marking systems– Very simple (manual) - Jitter

– General but still simple (StirMark)

• Idea is to be able to produce images very similarto the original except that it has the watermark

removed.• Another way of saying - Hacking!!



Early experiment—‘jitter’ attack

skytale:SysCoP$ imageread_demo syscop_watermarked.ppm Key:

No certificate file.-------------------------------------------------

A valid watermark found - estimated correction percentage is : 100Retrieved Secret Label (string) : SysCoP(TM)

skytale:SysCoP$ imageread_demo syscop_jitter.ppm Key:

No certificate file.-------------------------------------------------Cannon find valid watermark - failed.Image syscop_jitter.ppm has been tampered or hasnot been watermarked.

SysCoP



Jitter Attack

• Tweak the lower order bits and add jitter

• Split signal into number of chunks

• Duplicate or Delete at random• Imperceptible even in classical music!

• Jitter prevents marked bits from being

located



Jitter attack example

Watermarked Jitter added

SysCoP



StirMark

• Most watermarking schemes are robust to simplemanipulations:

• Rotation, cropping, rescaling,etc. …separately

• By using these transforms in tandem it’s possibleto distort the watermark



StirMark

– Apply minor geometric distortion:

o Stretching, shearing, shifting and rotation

o Simulate printing/scanning process

o Defeats most commercial image marking systems



Example

Original

JK_PGS(314,27) StirMark

PictureMarc 1.51, SysCoP (Demo), JK_PGS, SureSign, EIKONAmark (Pitas), NEC (Cox et al.)



Web crawlers for watermarks

• Interesting application– Web crawler download images

– Check whether they contain a watermark– Produce reports for copyright owners

e.g. MarcSpider by Digimarc, Portland, OR

• How do you prevent such crawlers from reporting your pictures?



Attacks on web-crawlers I

• ‘Mosaic’ attack – Designed to defeat systems combining watermarks and

web-crawlers

– Split images in small pieces (e.g. 100

100)– Each image is small enough that partial watermark cannotbe detected

– Confuse the mark detector

• Java applets/ActiveX objects

– Image displayed with Java applet automatically or aftercertain actions of the user– Can even be de-scrambled ‘on the fly’

• Refuse connection, login, payment



‘Mosaic’ attack



Conclusion

• First generation of copyright marking schemes isnot strong enough

• Existing schemes provide only limited measures ofmarking

• Can only meet few requirements at a time– Tradeoff - Bandwidth vs. robustness

– No single problem but a constellation!

• Real problem: watermark restoration