Saddle-point solution of the fingerprinting capacity game under the marking assumption

We study a fingerprinting game in which the collusion channel is unknown. The encoder embeds fingerprints into a host sequence and provides the decoder with the capability to trace back pirated copies to the colluders. Fingerprinting capacity has recently been derived as the limit value of a sequence of maxmin games with mutual information as the payoff function. However, these games generally do not admit saddle-point solutions and are very hard to solve numerically. Here under the so-called Boneh-Shaw marking assumption, we reformulate the capacity as the value of a single two-person zerosum game, and show that it is achieved by a saddle-point solution. If the maximal coalition size is k and the fingerprint alphabet is binary, we derive equations that can numerically solve the capacity game for arbitrary k. We also provide tight upper and lower bounds on the capacity. Finally, we discuss the asymptotic behavior of the fingerprinting game for large k and practical implementation issues.