Abstract

Abstract. This work presents threshold tracing schemes. Tracing schemes trace the source of keys which are used in pirate decoders for sensitive or proprietary data (such as pay-TV programs). Previous tracing schemes were designed to operate against any decoder which decrypts with a non-negligible success probability. We introduce threshold tracing schemes which are only designed to trace the source of keys of decoders which decrypt with probability greater than some threshold q (which is a parameter). These schemes present a dramatic reduction in the overhead compared to the previous constructions of tracing schemes. We argue that in many applications it is only required to protect against pirate decoders which have a decryption probability very close to 1 (for example, TV decoders). In such applications it is therefore very favorable to use threshold tracing schemes. 1

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