CAC ANNUAL MEETING DATA HIDING IN COMPRESSED MULTIMEDIA SIGNALS Bijan Mobasseri, PI S. R. Nelatury Dom Cinalli Dan Cross Aaron Evans Colin O’Connor Sathya Akunuru ECE Department Villanova University Villanova, PA October 30, 2002

2/46 Background info Funding agency: The US Air Force Office of Scientific Research(AFOSR) Monitor: AFRL/IFEC, Information Directorate, Rome, NY Project: Smart Digital Video PI: Bijan Mobasseri

3/46 Outline Data hiding/watermarking requirements Established watermarking approaches Project summaries: –Compressed media watermarking –Video authentication through self-watermarking –Lossless watermarking using error-resilient coding –Time-frequency watermarking –Metadata embedding

4/46 Data hiding/watermarking requirements Data hiding must at least meet the following three conditions: –Transparency; no visible impact on cover signal –Robustness; filtering, compression, cropping –Security; must assume the algorithm is known Places to hide data are: –Spatial- pixel amplitudes, LSB, QIM –Transform domain- spread spectrum, Fourier/wavelet, LPM –Joint- time/frequency distribution

5/46 Applications of watermarking Here are few, and growing list –Copyright protection- prevent unauthorized duplication –Fingerprinting-to find out who gave it away –Copy protection- to keep a tab on the number of copies made –Broadcast monitoring- automatic monitoring of commercials –Authentication- insuring data integrity and tamper resistance/detection –Indexing- helping multimedia search capability –Metadata hiding- embedding patient’s records in their medical images –Data hiding- covert communications in plain sight

6/46 Basic idea

7/46 Watermark Embedding and Extraction Cover image: f Watermark: w Embedding function:E Secret key:k Stego image= S=E(f,w,k) Authentication T(S): tampered signal

8/46 Detector response to forgeries Let’s say someone attempts to forge a watermarked document using their own signature We then have None of the two terms register significant response

9/46 Block Diagram Embedding Watermark extraction SOURCE WATER MARKING TAMPERING CORRUPTED WM SOURCE CORRUPTED WM SOURCE - SOURCE DISTORTED WM X ORIGINAL WM

10/46 Quality of extracted watermark

11/46 Trade-offs

12/46 LSB watermarking Probably the earliest attempt at watermarking was to flip the least significant bit of each pixel LSB being at noise level, would have no impact on quality. However, the slightest change in pixel intensity would make the watermark unreadable Pixel 1Pixel 2 LSB

13/46 BITPLANE WATERMAKRING

14/46 Hiding information in 24 bit images A 1024x bit color image can potentially hide 2,359,296 bits How would you hide the letter A? “A” can be hidden in the LSB of 3 pixels such as The binary value of A is Changed bits are shown

15/46 Transform domain watermarking Spatial watermarking is fast but brittle. It is best to do watermarking in transformed domains DFT –DCT –DWT The first successful implementation was done by Cox et al at NEC/Princeton under spread spectrum watermarking

16/46 Basic idea Instead of tweaking pixels, alter selected coefficients of image transform Then do inverse transform. This way, watermark spreads throughout the image affecting every pixel in some way It is not possible to find the watermark in the spatial domain

17/46 SPREAD SPECTRUM WATERMARKING (Cox, NEC) 55 DCT Quan Original frame

18/46 Challenges Which DCT coefficients should you choose? We have to worry about two competing requirements –Robustness - means low frequency terms should be modified –Imperceptibility - means low frequency terms should be avoided

19/46 DFT watermarking

20/46 Watermarking DWT

VIDEO WATERMAKING

22/46 Tampering scenarios: cut and splice of surveillance video A block of frames removed and video spliced Video must be embedded with proper sequencing codes so as to reveal the breakage

23/46 Cut, insert and splice Incriminating/sensitive portion is removed and replaced

24/46 Cut, swap and splice

25/46 Collusion attack

26/46 MPEG bitstream syntax

27/46 Embedding watermark bits in VLCs Variable length codes are the lynchpin of MPEG There is a subset of MPEG VLC codes that represent identical runs but differ in level by just one From: Langelaar et al, IEEE SP Magazine September 2000

28/46 Data hiding capacities

SELF-WATERMARKING * * D. Cross, B. Mobasseri, “Watermarking for self- authentication of compressed video,” IEEE ICIP2002, Rochester, NY, September 22-25, 2002,

30/46 Self-watermarking:the concept In self-watermarking, the watermark is extracted from the source itself Self-watermarking prevents watermark pirating Most work on self-watermarking has been done on images.

31/46 Self-watermarking of compressed video 10 VLC (0,5) VLC (0,16) VLC (1,15) VLC (0,6) VLC (1,10) VLC (1,11) VLC (0,12)

Lossless Watermarking of Compressed Media* * B. Mobasseri, D. Cinalli “Watermarking of Compressed Multimedia using Error- Resilient VLCs,” MMSP02, December 9-11, 2002

33/46 The idea:watermark as intentional bit errors A close look reveals that watermarking of VLCs is essentially equivalent to channel errors. Bit errors and watermark bits have identical impact. They both cause bit errors in affected VLCs.

34/46 The solution:lossless watermarking Embed watermark bits in the VLCs as controlled bit errors MPEG-2 VLCs, however, have no inherent error protection. Any bit error will cause detection failure up to start code Bidirectionally decodable codewords are capable of isolating and reversing channel errors This approach leads to lossless watermarking

35/46 Bi-directional VLCs Each VLC is represented twice in the new bitstream. It is this property that allows error resiliency Burst error shall not be so long to simultaneously affect the same bit of identical VLC

36/46 Watermarking capacity If watermarking begins with the first bit of the VLC and L=l, every bit of the VLC may be watermarked, then C=L bits/packet We define packet as one macroblock

37/46 Data

TIME-FREQUENCY WATERMARKING B. Mobasseri, “Digital watermarking in joint time-frequency domain,”,IEEE ICIP, Rochester, NY, September, 22-25, 2002

39/46 The Idea

40/46 TF watermarking WD + D WD - 1 WD WM JPEG

41/46 Results

42/46 Effect of compression JPEG:Q=5

Metadata Embedding

44/46 Background Video images & metadata recorded and handled as two separate streams –Storage overhead –Bookkeeping issues –Accuracy and human error –Cumbersome to display It would be nice to permanently attach metadata to video and make it available during playback Metadata Video

45/46 Sample Metadata and video footage Surveillance VideoXML Coded Metadata

THE END