Binary fingerprinting codes - can we prove that someone is guilty?!

The Identifiable Parent Property guarantees, with probability 1, the identification of at least one of the traitors by the corresponding traitor tracing schemes, or, by IPP-codes. Unfortunately, for the case of binary codes the IPP property does not hold even in the case of only two traitors. A recent work has considered a natural generalization of IPP-codes for the binary case, where the identifiable parent property should hold with probability almost 1. It has been shown that almost t-IPP codes of nonvanishing rate exist for the case t = 2. Surprisingly enough, collusion secure digital fingerprinting codes do not automatically possess this almost IPP property. In practice, this means that for a given forged fingerprint, say z, a user identified as guilty by the tracing algorithm can deny this claim since he will be able to present a coalition of users that can create the same z, but he does not belong to that coalition. In this paper, we study the case of t-almost IPP codes for t > 2.