1,469 research outputs found
Worst case attacks against binary probabilistic traitor tracing codes
An insightful view into the design of traitor tracing codes should
necessarily consider the worst case attacks that the colluders can lead. This
paper takes an information-theoretic point of view where the worst case attack
is defined as the collusion strategy minimizing the achievable rate of the
traitor tracing code. Two different decoders are envisaged, the joint decoder
and the simple decoder, as recently defined by P. Moulin
\cite{Moulin08universal}. Several classes of colluders are defined with
increasing power. The worst case attack is derived for each class and each
decoder when applied to Tardos' codes and a probabilistic version of the
Boneh-Shaw construction. This contextual study gives the real rates achievable
by the binary probabilistic traitor tracing codes. Attacks usually considered
in literature, such as majority or minority votes, are indeed largely
suboptimal. This article also shows the utmost importance of the time-sharing
concept in a probabilistic codes.Comment: submitted to IEEE Trans. on Information Forensics and Securit
Optimal sequential fingerprinting: Wald vs. Tardos
We study sequential collusion-resistant fingerprinting, where the
fingerprinting code is generated in advance but accusations may be made between
rounds, and show that in this setting both the dynamic Tardos scheme and
schemes building upon Wald's sequential probability ratio test (SPRT) are
asymptotically optimal. We further compare these two approaches to sequential
fingerprinting, highlighting differences between the two schemes. Based on
these differences, we argue that Wald's scheme should in general be preferred
over the dynamic Tardos scheme, even though both schemes have their merits. As
a side result, we derive an optimal sequential group testing method for the
classical model, which can easily be generalized to different group testing
models.Comment: 12 pages, 10 figure
Discrete Distributions in the Tardos Scheme, Revisited
The Tardos scheme is a well-known traitor tracing scheme to protect
copyrighted content against collusion attacks. The original scheme contained
some suboptimal design choices, such as the score function and the distribution
function used for generating the biases. Skoric et al. previously showed that a
symbol-symmetric score function leads to shorter codes, while Nuida et al.
obtained the optimal distribution functions for arbitrary coalition sizes.
Later, Nuida et al. showed that combining these results leads to even shorter
codes when the coalition size is small. We extend their analysis to the case of
large coalitions and prove that these optimal distributions converge to the
arcsine distribution, thus showing that the arcsine distribution is
asymptotically optimal in the symmetric Tardos scheme. We also present a new,
practical alternative to the discrete distributions of Nuida et al. and give a
comparison of the estimated lengths of the fingerprinting codes for each of
these distributions.Comment: 5 pages, 2 figure
Asymptotically false-positive-maximizing attack on non-binary Tardos codes
We use a method recently introduced by Simone and Skoric to study accusation
probabilities for non-binary Tardos fingerprinting codes. We generalize the
pre-computation steps in this approach to include a broad class of collusion
attack strategies. We analytically derive properties of a special attack that
asymptotically maximizes false accusation probabilities. We present numerical
results on sufficient code lengths for this attack, and explain the abrupt
transitions that occur in these results
Optimal symmetric Tardos traitor tracing schemes
For the Tardos traitor tracing scheme, we show that by combining the
symbol-symmetric accusation function of Skoric et al. with the improved
analysis of Blayer and Tassa we get further improvements. Our construction
gives codes that are up to 4 times shorter than Blayer and Tassa's, and up to 2
times shorter than the codes from Skoric et al. Asymptotically, we achieve the
theoretical optimal codelength for Tardos' distribution function and the
symmetric score function. For large coalitions, our codelengths are
asymptotically about 4.93% of Tardos' original codelengths, which also improves
upon results from Nuida et al.Comment: 16 pages, 1 figur
Towards joint decoding of binary Tardos fingerprinting codes
The class of joint decoder of probabilistic fingerprinting codes is of utmost
importance in theoretical papers to establish the concept of fingerprint
capacity. However, no implementation supporting a large user base is known to
date. This article presents an iterative decoder which is, as far as we are
aware of, the first practical attempt towards joint decoding. The
discriminative feature of the scores benefits on one hand from the
side-information of previously accused users, and on the other hand, from
recently introduced universal linear decoders for compound channels. Neither
the code construction nor the decoder make precise assumptions about the
collusion (size or strategy). The extension to incorporate soft outputs from
the watermarking layer is straightforward. An extensive experimental work
benchmarks the very good performance and offers a clear comparison with
previous state-of-the-art decoders.Comment: submitted to IEEE Trans. on Information Forensics and Security. -
typos corrected, one new plot, references added about ECC based
fingerprinting code
Dynamic Tardos Traitor Tracing Schemes
We construct binary dynamic traitor tracing schemes, where the number of
watermark bits needed to trace and disconnect any coalition of pirates is
quadratic in the number of pirates, and logarithmic in the total number of
users and the error probability. Our results improve upon results of Tassa, and
our schemes have several other advantages, such as being able to generate all
codewords in advance, a simple accusation method, and flexibility when the
feedback from the pirate network is delayed.Comment: 13 pages, 5 figure
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