Watermarking in E-commerce Systems

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 and authentication

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, graphics or multimedia, and carries information unique to the copyright owner, the creator of the document or the authorized consumer.

Example

Watermarking Vs Encryption

• Encryption involves document transformation so that the contents of the document are not visible without a decryption key

• Watermarking leaves the original file/image intact and 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 the

create the watermark and then embed in the document.

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

Digital Watermarking Applications (3)

• 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)

with patients name, ID.

Digital Watermarking Applications (4)

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

copies permitted.– Every time a copy is made the hardware modifies the

watermark and at the same time it would not create any more copies of the data.

– Commonly used in DVD technology.

• Content Protection– Content owner might want to publicly and freely

provide a preview 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 to prevent an attacker from finding and deleting it.

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

• Unambiguous: retrieval of it should unambiguously identify the data owner.

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

• Robust: difficult to remove for an attacker, who would like to destroy it in order to counterfeit the copyright of the data. Moreover, removal of it should cause a considerable degradation in the quality of the data.

• Visible watermarks should be visible enough to discourage theft.

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 of the pixels in the lower bit plane; e.g., Change some of the bits from 1 to 0 or 0 to 1.

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

Checksum Technique for images

• Watermark is formed from the 7 most significant bits of each 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 the watermark, W.

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

Example

Bavarian couple

Original Watermarked Version

Advantages/Disadvantages

• Embedding the checksum only changes (on average) half the number 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

size and checksum.• Entire watermark can be removed by removing the LSB

plane. Can’t survive lossy compression.

Attacks on Copyright Marking 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 similar to the original except that it has the watermark removed.

• Another way of saying - Hacking!!

Early experiment—‘jitter’ attack

skytale:SysCoP$ imageread_demo syscop_watermarked.ppmKey:

No certificate file.-------------------------------------------------A valid watermark found - estimated correction percentage is : 100Retrieved Secret Label (string) : SysCoP(TM)

skytale:SysCoP$ imageread_demo syscop_jitter.ppmKey:

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 simple manipulations:

• Rotation, cropping, rescaling,etc. …separately• By using these transforms in tandem it’s

possible to distort the watermark

StirMark

– Apply minor geometric distortion:o Stretching, shearing, shifting and rotationo Simulate printing/scanning processo 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. 100100)– Each image is small enough that partial watermark

cannot be detected– Confuse the mark detector

• Java applets/ActiveX objects– Image displayed with Java applet automatically or

after certain 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 is not strong enough

• Existing schemes provide only limited measures of marking

• Can only meet few requirements at a time– Tradeoff - Bandwidth vs. robustness– No single problem but a constellation!

• Real problem: watermark restoration