1. Confidential 1 Corporate Research © THOMSON multimedia, 1999 Mixing cryptography and watermarking for copy protection in consumer electronic devices FURON Teddy DIEHL Eric THOMSON multimedia R&D France {furont;diehle}@thmulti.com

2. Confidential 2 Corporate Research © THOMSON multimedia, 1999 Plan  Introduction  Limitations of encryption and watermark  A mixed approach: DVD-COPS  Public key like watermark?  Conclusion

3. Confidential 3 Corporate Research © THOMSON multimedia, 1999 Copy protection for CE devices  Every multimedia content will be digital Easily copied  Protection against illegal copy Four states to manage – Copy free, copy never, copy once, and copy no more Cost effective solution Keep Honest People Honest – Not against pirate organization  The aim is not To protect against copyright infringement To trace the pirate

4. Confidential 4 Corporate Research © THOMSON multimedia, 1999 Some proposed solutions  Mainly two classes of protection  Encryption based protection The content to protect is encrypted Duration of the protection varies – XCA: From reception till display – 5C’s DTCP: On the bus connecting two devices  Watermark based protection The watermark describes the copy status Handling of copy once varies – MILLENIUM: cryptographic ticket – GALAXY: additional watermark when recording

5. Confidential 5 Corporate Research © THOMSON multimedia, 1999 Plan  Introduction  Limitations of encryption and watermark  A mixed approach DVD-COPS  Public key like watermark?  Conclusion

6. Confidential 6 Corporate Research © THOMSON multimedia, 1999 Why encryption is not enough? CP Decryption key Original Content CP Encryption key Protected Content

7. Confidential 7 Corporate Research © THOMSON multimedia, 1999 Why Watermark is not enough? CP Original Content WM emb. WM emb. Watermarked Content WMdet. WMdet. WM det WM det

8. Confidential 8 Corporate Research © THOMSON multimedia, 1999 Plan  Introduction  Limitations of encryption and watermark  A mixed approach: DVD-COPS  Public key like watermark?  Conclusion

9. Confidential 9 Corporate Research © THOMSON multimedia, 1999 A mixed approach (1/3)  Protected creation by watermark & encryption Removing watermark is useless Breaking encryption is not sufficient  One bit payload Detection of presence of watermark  More robust then isolated protection #1 Personal creation Protected creation Free copy

10. Confidential 10 Corporate Research © THOMSON multimedia, 1999 A mixed approach (2/3)  A recordable medium carries only copies  Detection of media type Assume that media type is tamper proof #1 Personal creation Protected creation Free copy Original Copy No more copy #2

11. Confidential 11 Corporate Research © THOMSON multimedia, 1999 A mixed approach (3/3)  Digital signature protects “copy once”  Hacker has no interest to tamper or break the signature Bad signature means “copy never”  Using asymmetric cryptosystem Secret only for content owner #1 Personal creation Protected creation Free copy Original Copy Never copy No more copy Copy Once #2 #3

12. Confidential 12 Corporate Research © THOMSON multimedia, 1999 Plan  Introduction  Limitations of encryption and watermark  DVD-COPS: an example  Public key like watermark?  Conclusion

13. Confidential 13 Corporate Research © THOMSON multimedia, 1999 Public key like WM  Embedding ciphertext in watermark does not improve security Detection of watermark is weakest point  Applying cryptographic trap door function in signal processing is not possible.  Mimicking the basic ideas of public key crypto- system is the only way to succeed.

14. Confidential 14 Corporate Research © THOMSON multimedia, 1999 From cryptography to signal processing  Basic ideas in cryptography are: One way function Observe the effect, ignoring the cause.  How to achieve that with real signals? Filtering a Gaussian white noise is a one way operation (h n, v n )  w n = h n  v n The effect of filtering is noticeable in spectral analysis  ww( f ) ~ |H( f )| 2

15. Confidential 15 Corporate Research © THOMSON multimedia, 1999 Classical spread spectrum technique Transformation Cover Content Watermarked Content Adder Multiplier Human Perception Model Inverse Transformation Gaussian noise Private key

16. Confidential 16 Corporate Research © THOMSON multimedia, 1999 Improving SSWM scheme Embedding the WM Transformation Cover Content Watermarked Content Adder Multiplier Human Perception Model H filter Interleaver Gaussian noise Private key Inverse Transformation

17. Confidential 17 Corporate Research © THOMSON multimedia, 1999 Improving WMSS scheme Detecting the WM  The detection process is a test hypothesis in spectral analysis using a public key Transformation Content Interleaver Estimated Spectrum Test Hypothesis Y / N Public key

18. Confidential 18 Corporate Research © THOMSON multimedia, 1999 Plan  Introduction  Limitations of encryption and watermark  DVD-COPS: an example  Public key like watermark?  Conclusion

19. Confidential 19 Corporate Research © THOMSON multimedia, 1999 Conclusion J The CE device has now only public keys (signature and watermark). WM is robust because of low capacity  Extra constraints Copy Once on pressed media  The system is only based on switch decisions (Y / N). Can a switch be implemented securely in hardware? Can a switch be implemented securely in software?