Patent Document ID: 8516608
Application ID: 12800008
Patent Flag: 1

Claim One:
1. A method for decoding a probabilistic anti-collusion code intended to identify at least one sequence of said code present in a multimedia content having been used to create an illegal copy of said multimedia content, comprising: a) Creating two parameters namely: i. a vector of probabilities of the presence of a sequence in the collusion constituted, for each sequence of said code, of the probability of the presence of the sequence in a multimedia content having been used for the collusion, and ii. a vector of probabilities θ representing the collusion strategy constituted of an estimation of the number of sequences present in the collusion and of the conditional probabilities of observing such a symbol in the sequence of said illegal copy knowing the list of symbols of the sequences that are potentially present in the collusion; b) Initialising an iterative method by initialising at least one of the two parameters namely: i. initialising said vector of probabilities of the presence of a sequence in the collusion, initialising said vector of probabilities θ of the collusion strategy and starting of iterations by the step d) or, ii. initialising said vector of probabilities θ of the collusion strategy and starting of iterations by the step c); c) Estimating said parameter vector of probabilities of the presence of a sequence in the collusion using the sequence observed in the illegal copy, all of the sequences of said code and said parameter vector of probabilities θ of the collusion strategy, using a decoding device; d) Estimating said parameter vector of probabilities θ of the collusion strategy which maximizes the probability of the collusion strategy conditionally to said parameter vector of probabilities θ of the preceding iteration using the sequence contained in the illegal copy, all of the sequences of said code and said parameter vector of probabilities of the presence of a sequence in the collusion, using a decoding device; e) Iterating the steps c) and d) until a determined number of iterations or until convergence of the parameter vector of probabilities θ of the collusion strategy; and f) Identifying at least one sequence of said code present in a multimedia content having been used to create said illegal copy.