In the last part of the course we make a review of selected technical problems in multimedia signal processing First problem: CONTENT SECURITY AND WATERMARKING

DIGITAL CONTENT (AUDIO, VIDEO, GRAPHICS, IMAGES) CAN BE EASILY COPIED, TRANSMITTED AND DISTRIBUTED THIS HAS GREAT ADVANTAGES AND BUSINESS POTENTIAL, NO PHYSICAL MEDIA AND TRANSPORT IS NEEDED

EXAMPLE: Nokia Ovi store Buying music, movies, pictures, maps from the network means that content has to be protected against copying

DIGITAL MEDIA BRINGS ALSO BIG PROBLEMS FOR CONTENT OWNERS DUE TO UNAUTHORIZED USE. THEY CAN EASILY LOSE THEIR PROPERTY AND BUSINESS CONTENT OWNERS NEED THUS A STRONG PROTECTION OF THEIR CONTENT AGAINST UNAUTHORIZED USE

CONTENT PROTECTION IS QUITE DIFFICULT AND INCLUDES MANY ASPECTS THIS PROBLEM IS KNOWN CURRENTLY UNDER THE NAME DRM DIGITAL RIGHTS MANAGEMENT

WHAT ARE THE REQUIREMENTS FOR THE DRM? -DRM SHOULD PREVENT AGAINST COPYING -DRM SHOULD AUTHORIZE ACCESS LIMITED TO: PARTICULAR USER, SPECIFIC TIME, SPECIFIC NUMBER USAGE AND COPIES, ETC. -DRM SHOULD FACILITATE PAYMENT FOR CONTENT (E.G. RENTING FOR SPECIFIC TIME AND RENEWAL OF RIGHTS)

ALL REQUIREMENTS FOR DRM ARE VERY DIFFICULT TO SATISFY IN PARTICULAR THEY ARE DIFFICULT IF THE DRM SYSTEM WOULD BE STANDARDIZED, THAT IS IS STRUCTURE WOULD BE KNOWN TO EVERYBODY THIS IS BECAUSE STANDARDIZED SYSTEM MIGHT BE EASIER TO BREAK THAN SECRET SYSTEM

IN PRINICPLE DIGITAL CONTENT CAN BE EASILY (?) PROTECTED BY ENCRYPTION AND WATERMARKING WHAT IS ENCRYPTION? ENCRYTPION MEANS THAT THE CONTENT BITS ARE MANIPULATED IN SECRET WAY BY SOME ALOGRITHM.

THE ORIGINAL BITS CAN BE RECOVERED BY REVERSING THE OPERATION OF THE ALGORITHM, REVERSE ALGORITHM IS CALLED DECRYPTION SO WE HAVE TWO ALGORITHMS WHICH CAN REVERSE: CONTENT ENCRYPTION ALGORITHM DECRYPTION ALGORITHM CONTENT

BUT SUCH SYSTEM HAS PROBLEMS 1.IF ALGORITHM IS KNOWN, EVERYBODY WILL USE IT 2.HOW TO CONTROL THE ACCESS TO CONTENT? WHAT IF USERS BUY ACCESS FOR SOME TIME AND FOR SOME CONTENT ONLY? 3.WHAT TO DO WITH USERS WHICH WILL USE PROPER ACCESS FOR ILLEGAL COPYING AND DISTRIBUTION OF CONTENT?

THUS THE DRM CONTENT PROTECTION MUST BE MORE CLEVER. IT HAS TO BE BASED ON 1.CONDITIONAL ACCESS 2.ENCRYPTION ALGORITHMS 2.WATERMARKING

WHAT IS CONDITIONAL ACCESS? IT IS ACCESS GIVEN ON LIMITED CONDITIONS, E.G. TIME, CONTENT, PAYMENT AND SO ON CONTENT ENCRYPTION ALGORITHM DECRYPTION ALGORITHM CONDITIONAL ACCESS ENABLED AFTER PAYING CONDITIONAL ACCESS CAN BE A CARD GIVEN TO THE USER, OR A CERTIFICATE SEND VIA INTERNET

EXAMPLE – THE SYSTEM USED IN DIGITAL TELEVISION FOR WATCHING PAY PROGRAMS, IN THIS SYSTEM CONDITIONAL ACCESS HAS A FORM OF SUBSCRIPTION CARD, ON THE CARD THERE IS PROCESSOR IMPLEMENTING PART OF CA SYSTEM ANOTHER PART IS IMPLEMENTED IN A MODULE CALLED CAM – CONDITIONAL ACCESS SYSTEM, THE CARD SLIDS INTO THE CAM. THIS MODULE MAKES POSSIBLE TO USE DIFFERENT CA ALGORITHMS BY DIFFERENT OPERATORS

CAM MODULE SUBSCRIPTION CARD RECEIVER FOR DIGITAL TELEVISION

ONE RECEIVER CAN ALSO HAVE SEVERAL CAM’s WITH CARDS FOR RECEIVING PAY PACKAGES FROM DIFFERENT OPERATORS. SUCH SYSTEMS ARE WIDELY USED IN TELEVISION. BUT MANY OF THE SYSTEMS WERE ALSO BROKEN SINCE ONE CAN ANALYZE PROGRAM ON THE CARD AND TRACE TRAFFIC BETWEEN THE CARD AND CAM.

ENHANCED SOLUTION: AUTHENTICATE THE USER THIS CAN BE DONE IF THE USER IS CONNECTED TO THE TELEPHONE OR THE INTERNET, THE SYSTEM CAN CHECK IF THE ORIGINAL CARD IS USED.

BUT WHAT TO DO IF A USER HAS VALID SUBSCRIPTION BUT USES IT FOR RECORDING AND DISTRIBUTING CONTENT ILLEGALLY? IN THIS CASE WE CAN NOT PROTECT THE CONTENT ONE SOLUTION IS TO PREVENT RECORDING AND/OR TO PREVENT GETTING THE RECORDING OUT OF THE DEVICE

FOR EXAMPLE IN MEDIA TERMINAL USER CAN RECORD DIGITAL TV PROGRAMS ON INTERNAL HARD DISC BUT RECORDED CONTENT IS ENCRYPTED AND THERE IS NO WAY OF GETTING IT OUT OF THE TERMINAL STILL, HACKERS MAY BE ABLE TO BREAK SUCH SYSTEM TOO

THUS, TO PROTECT THE CONTENT TECHNICALLY MIGHT BE SOMETIMES DIFFICULT OR EVEN IMPOSSIBLE THE ONLY WAY TO DEAL WITH IT COULD BE MARKING THE CONTENT IN AN INVISIBLE WAY TO DETECT WHO AND WHEN COPIED IT. THIS CAN BE USED AS A PROOF FOR CRIMINAL OFFENCE AND FOR USING LEGAL MEANS TO PROTECT THE CONTENT OWNER

THE OVERALL PROBLEM OF DRM IS A COMPLEX TECHNICAL AND LEGAL PROBLEM MANY OF ITS ASPECTS ARE OUTSIDE OF SIGNAL PROCESSING, THEY BELONG TO COMPUTER AND NETWORK SECURITY AREA BUT HOW TO MARK THE CONTENT IN SECRET WAY IS A SIGNAL PROCESSING PROBLEM

MARKING OBJECTS IN AN INVISIBLE WAY IS CALLED WATERMARKING WATERMARKING IS A WORD COMING FROM PAPER MONEY WHICH IS MARKED IN SUCH A WAY THAT IT IS VISIBLE UNDER BACKLIGHT OUR PROBLEM HERE IS HOW TO MAKE DIGITAL WATERMARKING?

Why to use watermarks ? Ease of replication Ease of transmission and multiple use Plasticity (easy to change format) Equivalence of works in digital form Because digital media have following features making easy copyright violations:

Digital Watermark definition A method of embedding a copyright stamp into an image, sound or video. The watermark is embedded such that the quality of the host media is not noticeably degraded to the human eye/ear.

Uses of Watermarking Copyrighting embedding Data hiding (Steganography) Source/ownership verification

Requirements for Good Watermarks Imperceptible Undeletable Statistically Undetectable Robust to Lossy Data Compression Robust to Signal Manipulation and Processing Operations Unambiguous Readily detectable Unobtrusive Innumerable

What Watermarking Allows Allows authors/artists to mark their work as their own Allows companies to verify source/origin of media on a website, detect plagiarism/copyright infringement Allows receiver to verify authenticity of media

Watermarking Techniques Examples Least-significant-bit (LSB) insertion and noise manipulation –Can insert a lot of data if image is simple –Not very robust Discrete Cosine Transformation (DCT) –Very robust –Can’t insert large amounts of data

Watermarking Example Original GIF photo (97KB) Photo containing 53KB of text (80KB) Using Least-Significant-Bit (LSB)

Watermarking Example 2 Original Photo (24KB) Photo containing 29KB of text (29KB) Using Least-Significant-Bit (LSB)

Watermarking Techniques Examples Least-significant-bit (LSB) insertion and noise manipulation –Can insert a lot of data if image is simple –Not very robust Discrete Cosine Transformation (DCT) –Very robust –Can’t insert large amounts of data NEXT

FROM THE DIFFERENTIAL PICTURE ONE CAN EXTRACT THE WATERMARK BUT...

PEOPLE MAY TRY TO ATTACK THE WATERMARK EVEN IF THEY DO NOT KNOW HOW IT IS DONE FOR EXAMPLE, THEY MAY COMPRESS THE PICTURE OR ENLARGE IT WATERMARK SHOULD BE ROBUST AGAINST THESE ATTEMPT THIS IS SHOWN IN THE NEXT EXAMPLES

RESPONSE TO MANY WATERMARKS

Watermarking Example 3 Original JPEG photo (32KB) Photo containing 1 line copyright info (33 KB) Using Discrete Cosine Transformation (DCT)

Video Watermarking DCT-Based Video Watermarking –MPEG-based method

CONCLUSION PRESERVING COPYRIGHT WILL BE MORE AND MORE IMPORTANT AT PRESENT THERE ARE NO SYSTEMS WHICH WOULD BE RESISTANT TO ALL COPYRIGHT ATTACKS WATERMARKS CAN BE PRODUCED BUT THE ACTUAL METHODS ARE SECRET