A novel key refreshment scheme increasing the security of conditional access systems in digital satellite pay-TV

This paper proposes a new scheme that faces one of the basic deficiencies of Conditional Access Systems (CASs) employed in satellite Pay-TV systems, Master Private Key´s (MPK) infinite crypto period. The novelty of the proposed scheme is that it offers the ability to the administrator of the CAS to refresh users´ MPKs at desired times. Thereby, the security of the CAS is significantly increased. The refreshment of the MPKs is accomplished through Lagrange Interpolation Method (LIM). In addition, the bandwidth consumption of several contemporary CASs of the Pay-TV market is presented. Based on those measurements, the bandwidth overhead that the new scheme imposes is proven to be negligible. The efficiency of the LIM for the refreshment of the MPK is verified through its implementation on a 65 nm Field Programmable Gate Array (FPGA). Finally, the required user´s MPK refreshment time was achieved to be less than 0.15 ms.