A decoder decrypts data from the stream of data, using decryption control words. A secure device is coupled to the decoder to supply the control words. The secure device has a memory space for storing at least two items of entitlement information with associated authorization keys. The secure device has an input for receiving messages from the apparatus. The message contains information for example about the source of the stream. The secure device contains an execution unit that responds to the messages by selecting from among die at least two items, if stored, dependent on a content of the messages. The execution unit enables sending of the control words to the decoder subject to the presence and validity of the selected one of the items of entitlement information, after decryption of the control word with a decryption key associated with the selected one of the items.