A public-key black-box traitor tracing scheme with sublinear ciphertext size against self-defensive pirates

We propose a public-key traitor tracing scheme in which (1) the size of a ciphertext is sublinear in the number of receivers and (2) black-box tracing is efficiently achieved against self-defensive pirate decoders. When assuming that a pirate decoder can take some self-defensive reaction (e.g., erasing all of the internal keys and shutting down) to escape from tracing if it detects tracing, it has been an open question to construct a sublinear black-box traitor tracing scheme that can detect efficiently at least one traitor (who builds the pirate decoder) with overwhelming probability, although a tracing algorithm that works successfully against self-defensive pirate decoders itself is known. In this paper, we answer affirmatively the above question by presenting a concrete construction of a public-key black-box tracing scheme in which the known tracing algorithm can be used while keeping the size of a ciphertext sublinear.