Infoscience

Thesis

Broadcast Encryption and Traitor Tracing for Conditional Access Systems

In the context of the thesis we are studying the notions of broadcast encryption and traitor tracing in an industrial framework of conditional access systems related to Pay-TV. Broadcast encryption represents a cryptographic primitive which allows confidential transmission of content on a broadcast channel in such a way that only an authorized subset of users defined by the broadcaster are able to access it. Traitor tracing is a mechanism for identifying rogue sources who shared their decryption keys. Combined together, these two methods can be used to identify compromised terminals and instantaneously revoke them. Intuitively these two techniques are of high interest for Pay-TV systems with respect to the threats of today. Today, the majority of industrial security system are based on the tamper-resistance against attacks, such as those exploiting, for instance, different side channel information such as time, power consumption, electromagnetic emanations to name a few. However during recent years these attacks became more and more sophisticated. Therefore the aim of this thesis is to propose new schemes and mechanisms to improve the state-of-the-art for the conditional access systems and more specifically Pay-TV systems so that they rely even more on a solid cryptographic basis. As a matter of fact, even though many cryptographic schemes closely related to the subject of this thesis existed since many years in academia, none of them could have been deployed directly and efficiently in the context of large scale Pay-TV system which puts a number of heavy constraints on the bandwidth as well as on the computational complexity of the receivers. Consequently we will also describe the system and its constraints in order to simplify the task of development and integration of future schemes in these two academic domains in the context of practical environment.

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