Abstract:
This project presents a new scrambling scheme and a new key distribution scheme. Both are parts of the conditional access system (CAS) that is used to prevent unauthorized access to pay-TV systems. The first part is our new scrambling scheme. It is used in conjunction with ordinary encryption techniques, for protecting the digital video streams from unauthorized viewing. Because video streams have much higher bit rate than other type of information such as text, it is often very difficult to directly implement a complicated type of encryption algorithms on the video streams. Our proposed scheme helps reduce computational time and complexity while providing the same level of security as encrypting the entire video stream. A strong collision one way hash function and a pseudo-random number generator are used to prepare the video stream before being encrypted. The second part in this thesis is on the key distribution scheme. It addresses the security problems that occur in the Pay-TV systems, particularly when a decoder box is used along with a smart card. Using these two devices together could give a weakness to the system since the information transfer between them can be tapped and then used to break the system. This is known as McCormac Hack. Furthermore, the smart card can be cloned and then used with other decoder boxes to gain access to the services. Our key distribution scheme is successful in preventing these two problems. It is divided into two sub-schemes: one that is used with our scrambling scheme and another that can be used with other scrambling schemes. In addition, Chinese Remainder Theorem and discrete logarithm are used to increase the security in distribution parameters in the scrambling process.