Zenith Electronics Corporation

Harry A Hartley, Iii

Khosro M Rabii

Caitlin B Bestler

A subscriber terminal includes a digital conditional access module receiving a transport bitstream comprising a plurality of multiplexed conditional access and product packets. Selected ones of the conditional access packets are addressed to respective terminals and include an encrypted new decryption key code, an encrypted authorization bit map and an authorization list range delete code. The conditional access packets are decrypted by the conditional access modules of respective addressed terminals, the decrypted new decryption key code being stored for subsequent use by the conditional access module, the decrypted authorization bit map being used to refresh the authorization bit map memory of the module and the decrypted delete code being used to delete a specified range of authorization codes from the authorization list memory of the module.

System for updating an authorization memory

A digital conditional access module for a subscriber terminal comprises a decryption device including at least one PID register and an associated countdown register. The decryption device is enabled for decrypting received product packets having a PID matching a PID stored in the PID register so long as the associated countdown register is characterized by a non-zero value. Decryption of a product packet results in the countdown register being decremented by a selected factor, the countdown register being prevented from assuming a zero value by setting its contents to a selected value in response to a received conditional access packet containing a PID matching the PID stored in the PID register. The selected value to which the countdown register is set may also be contained within the received conditional access packet.

Countdown system for conditional access module

Upstream transmissions in a two-way communications network are effected from subscriber terminals in upstream packets having one of a plurality of different separately acknowledgeable acknowledgment tags. Downstream acknowledgments of upstream messages are contained in CA packets multiplexed with product packets to form a transport bitstream. The transport bitstream is applied to a digital conditional access module (DCAM) in the terminal which is controlled by the conditional access data bits of the CA packets. The DCAM includes a status register for storing the acknowledgment bits of the CA packets, which bits are coupled by a microprocessor for controlling the upstream transmitter.

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Palatine, IL, United States of America

Harry A Hartley, Iii