ABSTRACT
The Digital Video Broadcasting standard envisages the transmission of access control data carried by the conditional access table and other private data packets indicated by the program map table. The conditional access itself is not defined by the standard, as most operators did not want a common system, everyone guarding jealously their own system for both commercial and security reasons. The standard also defines a common scrambling algorithm for which the trade-off between cost and complexity has been chosen in order that piracy can be resisted for an appropriate length of time. The information required for descrambling is transmitted in specific conditional access messages, which are of two types: entitlement control messages and entitlement management messages. The scrambling algorithm uses two control words (even and odd) alternated with a frequency of the order of 2 s in order to make the pirate's task more difficult.
