| 摘要 |
A source transmits ( 10 ) successive keys encrypted in encryption control messages and information in an encrypted form at is successively decryptable with the successive keys. A decoder ( 122 ) decrypts the information. A secure device ( 14 ) receives the encryption control messages, decrypts the keys from the messages and supplies the keys to the decoder ( 122 ). The secure device ( 14 ) maintains a time value. The secure device ( 14 ) controls the supply of the keys dependent on the time value, and increments the time value in response to reception of respective ones of the encryption control messages.
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