Conditional-access broadcast transmission

摘要

A conditional-access television receiver includes a descrambler circuit 10 which is enabled by descrambler control signals received from a conditional access-sub-system (CASS). The descrambler control signals are derived from off-air control data signals by a decryption circuit 31 responsive to a key. The key is formed in each receiver in a matrix 34 by combining a personal identification number (PIN) with a CASS code read from a CASS store 35. The appropriate CASS code is selected by further broadcast data. Alternatively a pre-payment or direct debit accounting system can be used.