Strongly separable codes

Binary t-frameproof codes (t-FPCs) are used in multimedia fingerprinting schemes where the identification of authorized users taking part in the averaging collusion attack is required. In this paper, a binary strongly t-separable code (t-SSC) is introduced to improve such a scheme based on a binary t-FPC. A binary t-SSC has the same traceability as a binary t-FPC but has more codewords than a binary t-FPC. A composition construction for binary t-SSCs from q-ary t-SSCs is described, which stimulates the research on q-ary t-SSCs with short length. Several infinite series of optimal q-ary 2-SSCs of length 2 are derived from the fact that a q-ary 2-SSC of length 2 is equivalent to a q-ary 2-separable code of length 2. Combinatorial properties of q-ary 2-SSCs of length 3 are investigated, and a construction for q-ary 2-SSCs of length 3 is provided. These 2-SSCs of length 3 have more than 12.5% codewords than 2-FPCs of length 3 could have. Index Terms Multimedia fingerprinting, separable code, strongly separable code, frameproof code, tracing algorithm