| 摘要 |
A three key cryptographic system is used in the transmission of digitized signals to a plurality of receivers, each having a unique address number and a factory stored signature key which is a function of the address number. At the transmission end, a common key is generated (14) and used to encrypt (16) the signals to be transmitted. The signature key is generated (20, 22) for each receiver unit by encrypting the address number of the unit (18) using a secret master key (20). The common key is then encrypted (16) for use by each receiver using the generated signature key for that receiver. A data stream is inserted into the horizontal blanking intervals of the composite video signal. The data stream includes the encrypted signals receivable by all receivers and addressed portions, each receivable by a different receiver, containing the encrypted common key for that receiver. The receiver decrypts (26) the common key with the stored signature key and uses it to decrypt (24) the signals. Only a single master key must be stored and protected. |
