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摘要

A decoder conditional access system incorporates different encryption systems for providing access to programs derived from different sources. A conditional access processor for processing encrypted program data and an associated encryption code includes a first algorithm means for decrypting the encryption code to provide an encryption key. The conditional access processor also includes a second algorithm means for encrypting the encryption key and the second encryption algorithm is different to the first encryption algorithm. A datastream representing the program is generated from encrypted program data and an associated encryption code. The encryption code is decrypted to provide an encryption key using a first algorithm. The encryption key is encrypted using a second algorithm different to the first encryption algorithm and the program datastream is formed from the encrypted program data and the encrypted encryption key. The program datastream is decrypted by selecting between a first and a second decryption algorithm and by decrypting the encryption code to provide an encryption key. The encryption key is used to decrypt the encrypted program. A storage medium data format for recording encrypted program data is also disclosed.