Patent ID: 7809942

Claim:
A conditional access method for use with a system for controlling of digital television program start time, for authorizing subscriber access to digital program streams, comprising the steps of: dividing content into a plurality of working periods; scrambling different working periods of the plurality of working periods with a different working keys, with the working keys synchronized with scrambling control bits in a content packet header; inserting working keys into entitlement control message (ECM) packets; encrypting the ECM packet using service keys at a distribution hub that uses quadrature amplitude modulation to deliver at least video on demand to a particular subscriber cluster; delivering the working keys via a network to subscriber devices ahead of the working periods to which they apply; inserting, in an entitlement management message (EMM) packet, a service key for decrypting the ECM packets; encrypting the EMM packet using a user-specific key for an individual subscriber device to which the EMM packet is sent; periodically sending EMM packets having new service keys usable by a group of individual subscribers from the distribution hub via a network to the subscriber devices, such that the new service keys have a limited distribution area, which reduces incentives for pirating; and authenticating the EMM packet with a digital signature of a valid headend.