A secure content delivery system, comprising: a set-top box to initiate a request for program data, the request including a unique identifier of the set-top box, the set-top box having a memory storing a unique key of the set-top box; and a conditional access control system in communication with the set-top box and a mating key server, the CA control system configured: to transmit information including the unique identifier and a mating key generator to the mating key server, to receive from the mating key server a mating key being based on the transmitted unique identifier and the mating key generator, the mating key being used to encrypt a control word used for scrambling the program data prior to transmission to the set-top box the mating key obtained by the mating key server accessing a copy of the unique key stored in the mating key server, and encrypting the mating key generator using the copy of the unique key, and to transmit the mating key generator and the encrypted control word to the set-top box; the set-top box configured to encrypt the received mating key generator using the unique key to obtain a key identical to the mating key, to use the obtained mating key to decrypt the encrypted control word, and to use the decrypted control word to descramble scrambled program data. a set-top box to initiate a request for program data, the request including a unique identifier of the set-top box, the set-top box having a memory storing a unique key of the set-top box; and a conditional access control system in communication with the set-top box and a mating key server, the CA control system configured: to transmit information including the unique identifier and a mating key generator to the mating key server, to receive from the mating key server a mating key being based on the transmitted unique identifier and the mating key generator, the mating key being used to encrypt a control word used for scrambling the program data prior to transmission to the set-top box the mating key obtained by the mating key server accessing a copy of the unique key stored in the mating key server, and encrypting the mating key generator using the copy of the unique key, and to transmit the mating key generator and the encrypted control word to the set-top box; to transmit information including the unique identifier and a mating key generator to the mating key server, to receive from the mating key server a mating key being based on the transmitted unique identifier and the mating key generator, the mating key being used to encrypt a control word used for scrambling the program data prior to transmission to the set-top box the mating key obtained by the mating key server accessing a copy of the unique key stored in the mating key server, and encrypting the mating key generator using the copy of the unique key, and to transmit the mating key generator and the encrypted control word to the set-top box; the set-top box configured to encrypt the received mating key generator using the unique key to obtain a key identical to the mating key, to use the obtained mating key to decrypt the encrypted control word, and to use the decrypted control word to descramble scrambled program data.