CONDITIONAL ENTITLEMENT PROCESSING FOR OBTAINING A CONTROL WORD

摘要

The invention provides an improved method and an improved receiver for obtaining a control word. Two or more subkeys are obtained in a receiver. Each subkey was encrypted under control of a key received in an entitlement message or transformed under control of a seed received in an entitlement message. After decryption or transformation, the subkeys are combined to obtain the control word. Typically at least one of the entitlement messages is a positive entitlement message and at least one of the entitlement messages is a negative entitlement message. The invention can be used in a conditional access system such as a Pay-TV system.