Traitor Tracing Scheme Secure against Adaptive Key Exposure and its Application to Anywhere TV Service

Kazuto OGAWA  Goichiro HANAOKA  Hideki IMAI  

IEICE TRANSACTIONS on Fundamentals of Electronics, Communications and Computer Sciences   Vol.E90-A   No.5   pp.1000-1011
Publication Date: 2007/05/01
Online ISSN: 1745-1337
DOI: 10.1093/ietfec/e90-a.5.1000
Print ISSN: 0916-8508
Type of Manuscript: Special Section PAPER (Special Section on Discrete Mathematics and Its Applications)
traitor tracing,  key exposure,  key update,  two variable-polynomial,  

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Copyright protection is a major issue in distributing content on Internet or broadcasting service. One well-known method of protecting copyright is a traitor tracing scheme. With this scheme, if a pirate decoder is made, the content provider can check the secret key contained in it and trace the authorized user/subscriber (traitor). Furthermore, users require that they could obtain services anywhere they want (Anywhere TV). For this purpose, they would need to take along their secret keys and therefore key exposure has to be kept in mind. As one of countermeasures against key exposure, a forward secure public key cryptosystem has been developed. In this system, the user secret key remains valid for a limited period of time. It means that even if it is exposed, the user would be affected only for the limited time period. In this paper, we propose a traitor tracing scheme secure against adaptive key exposure (TTaKE) which contains the properties of both a traitor tracing scheme and a forward secure public key cryptosystem. It is constructed by using two polynomials with two variables to generate user secret keys. Its security proof is constructed from scratch. Moreover we confirmed its efficiency through comparisons. Finally, we show the way how its building blocks can be applied to anywhere TV service. Its structure fits current broadcasting systems.