Fun Stuff: Digital Media Cryptography Lecture 3: Chantilly Academy Poorvi Vora Department of Computer Science George Washington University

Crypto Lecture 3: Spring 07 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

Crypto Lecture 3: Spring 07 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

Crypto Lecture 3: Spring 07 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

Crypto Lecture 3: Spring 07 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

Crypto Lecture 3: Spring 07 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

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 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

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; 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

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 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

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. 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

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 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

Crypto Lecture 3: Spring 07 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

Crypto Lecture 3: Spring 07 Another problem: Authentication of digital media given cheap access to capable processing systems Was this image changed in any way after it was captured? 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07

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 5/9/2019 Chantilly Academy Crypto Lecture 3: Spring 07