A cable television system provides conditional access to services. The cable television system includes a headend from which service "instances", or programs, are broadcast and a plurality of set top units for receiving the instances and selectively decrypting the instances for display to system subscribers....http://www.google.fr/patents/US6252964?utm_source=gb-gplus-shareBrevet US6252964 - Authorization of services in a conditional access system
Authorization of services in a conditional access system
