Patent ID: 7509682

Claim:
A copy protection method for digital media, the method comprising the steps of: (a) encrypting an original media data set with a media key corresponding to a symmetric algorithm and encrypting said media key with a public key of a compliant playing device; (b) delivering said media data set, media key encrypted in the step (a), a media certificate, and a key renewing certificate to said playing device, said media certificate being required to recognize by said playing device a valid private key among a plurality of private keys stored in said playing device and including a private-key identification and media identification of said playing device, said private-key identification being generated by encrypting said media identification with said public key of said playing device, wherein said key renewing certificate is required to update a private key of said playing device and including a pair of new public key and private key of said playing device and a time mark for sequencing said public and private keys from the oldest to the newest, respectively; (c) searching for an actual private key using said private-key identification and said media identification; (d) decrypting said delivered media key with said actual private key; and (e) decrypting said delivered media data set with said decrypted media key; (f) processing said key renewing certificate using a master private key of said playing device, and analyzing said time mark; (g) replacing a pair of current public and private keys of said playing device with said pair of new public and private keys if said key renewing certificate is the newest one as a result of analysis; and (h) encrypting said master private key with said new public key of said playing device.