the holey grail a special score function for non-binary traitor tracing boris Škorić jan-jaap...
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The Holey Grail
A special score function for non-binary traitor tracing
Boris Škorić
Jan-Jaap Oosterwijk
Jeroen Doumen
/ Department of Mathematics & ComputerScience
Piracy
• Copy protection• Illegal or unofficial copy• Traitor tracing
20-11-2013 PAGE 2
/ Department of Mathematics & ComputerScience
Traitor Tracing
• Watermark embedding: user ID• Pirate copy• Watermark extraction: pirate ID
• Watermark removal must be difficult• Watermark distortion must be difficult• Watermark detection must be difficult
• Embed throughout the content in secret locations• Segment the content• Per segment, two versions: and
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User ID ...
/ Department of Mathematics & ComputerScience
Collusion
• Compare several watermarked copies• Locate the differences• Create new watermark
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Ingrid ...
Pierre ...
Travis ...
New
/ Department of Mathematics & ComputerScience
Collusion-Resistant Traitor Tracing
• Detecting the entire user ID should be difficult• The differences should not occur in all the
watermark locations
• Embed a random code• Per segment:
• or
• Probability distribution
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0.9 0.8 0.1 0.4 ...
Ingrid ...
Pierre ...
Travis ...
New ...
/ Department of Mathematics & ComputerScience
Collusion-Resistant Traitor Tracing (II)
• Compare the collusion watermark to all user watermarks
• Attribute a level of suspicion to each user• Accuse users that are too suspicious
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/ Department of Mathematics & ComputerScience
Level of suspicion
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0
guilty
innocent
level of suspicion
FN FP
accusation threshold
/ Department of Mathematics & ComputerScience
Code length
• The larger the coalition, the more difficult the tracing.
• 2003, Tardos: Possible to trace at least one of colluders, with error probabilities bounded by and using a code of length
20-11-2013 PAGE 8
/ Department of Mathematics & ComputerScience
Nice properties
• Level of suspicion of innocent users• Zero mean (independent of collusion strategy)• Unit variance (independent of collusion strategy)
• Level of suspicion of coalition• Mean is independent of collusion strategy
20-11-2013 PAGE 9
/ Department of Mathematics & ComputerScience
Larger alphabets
• Using larger alphabets allows for better schemes.• 2011, Boesten et al.: Fingerprinting capacity increases• 2013, Oosterwijk et al.: Capacity-achieving scheme
• But... mean level of suspicion of coalition does depend on the collusion strategy
20-11-2013 PAGE 10
/ Department of Mathematics & ComputerScience
Traitor Tracing Scheme
• Probability distribution • Bias
• Suspicion function • X is the version assigned to user• Y is the version chosen by coalition
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/ Department of Mathematics & ComputerScience
The Grails
• Any probability density function • Level of suspicion
• Binary: Tardos scheme is not the only one!• Non-binary: We finally found a scheme (and more!)
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/ Department of Mathematics & ComputerScience
Holy Grail
• For large coalitions, the optimal scheme is
• Binary: Tardos
• Non-binary:
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/ Department of Mathematics & ComputerScience
Holey Grail
• We regret to inform you that this grail has holes
• Using larger alphabets, allows for better schemes• But...• The fingerprinting rate of this grail decreases with
20-11-2013 PAGE 14
/ Department of Mathematics & ComputerScience
Conclusion
• Collusion-Resistant Traitor Tracing Scheme
• Level of suspicion of innocent users• Zero mean (independent of collusion strategy)• Unit variance (independent of collusion strategy)
• Level of suspicion of coalition• Mean is independent of collusion strategy
• Possible for non-binary alphabets, but this construction performs worse than was hoped.
20-11-2013 PAGE 15
Thanks for your attention!
Questions?
EURASIP Journal on Information Security
Topics are among others
o Collusion Secure Fingerprinting codes
o Transactional Watermarking and Traitor Tracing
o Collusion Secure Watermarking
o Transactional Watermarking and Fingerprinting for
data sets / sets of files
o Real World reports or experiences or insights
regarding the legal perspective
http://jis.eurasipjournals.com/
Guest-editors:Boris Škorić, Eindhoven Univ. of Tech.
Jan-Jaap Oosterwijk,Eindhoven Univ. of Tech.
Thijs Laarhoven,Eindhoven Univ. of Tech.
Jeroen Doumen, Irdeto BV
Waldemar Berchtold,Fraunhofer Institute SIT
Martin Steinebach,Fraunhofer Institute SIT
Marcel Schäfer, Fraunhofer Institute SIT
Editor-in-Chief:Stefan Katzenbeisser,TU-Darmstadt
CfP: Special Issue on
Collusion Secure Fingerprinting
and Transactional Watermarking
Deadline for submissions, February 28, 2014