Optimal probabilistic fingerprint codes

We construct binary codes for fingerprinting. Our codes for n users that are ε-secure against c pirates have length O(c2 log(n/ε)). This improves the codes proposed by Boneh and Shaw [3] whose length is approximately the square of this length. Our codes are probabilistic. By proving matching lower bounds we establish that the length of these codes is best within a constant factor for reasonable error probabilities. This lower bound generalizes the bound found independently by Peikert, Shelat, and Smith [10] that applies to a limited class of codes. Our results also imply that randomized fingerprint codes over a binary alphabet are as powerful as over an arbitrary alphabet, and also the equal strength of two distinct models for fingerprinting.