Abstract: A system for decrypting an encrypted message comprises first and second decryption devices, the first decryption device having a higher security than the second decryption device. The system further comprises means for dividing the encrypted message into blocks, and means for providing at least the first block of the message to the first decryption device and for providing a plurality of further blocks of this message to the second decryption device. An output of the first decryption device is used as input of the second decryption device. The second decryption device operates according to a block chaining method for decrypting the plurality of further blocks.

Abstract: A system for broadcasting data signals in a secure manner comprises means for encrypting the data signals using a first key, means for broadcasting the encrypted data signals to subscribers, means for decrypting the encrypted data signals at each of the subscribers using the first key, and means for encrypting the first key using a second key. The second key is different for each group of subscribers having a common interest in a type of programs. The system further comprises means for broadcasting the encrypted first key to all subscribers and means for decrypting the encrypted first key at each of the subscribers using the second key. The second key is a combination of a key common to all subscribers and a difference key which is unique per type of programs. Means are provided for encrypting the common key and for broadcasting the encrypted common key to all subscribers, the subscribers having means for decrypting the encrypted common key at each of the subscribers.