Patent ID: 7239709

Claim:
A data recording/reproducing system comprising: contents encrypting means for receiving digital data and for using a contents key to generate encrypted digital data; a key-encrypting key generating means for generating a plurality of key-encrypting keys for a predetermined period, each of said plurality of key-encrypting keys is different from each other, for subjecting said content key to second encrypting; a storing means for storing said generated plurality of key-encrypting keys and for making invalid each of said key-encrypting keys in sequence, while leaving the encrypted digital data hereafter if each of said key-encrypting keys satisfies a corresponding predetermined condition respectively; key encrypting means for generating an encrypted contents key by subjecting said contents key to said second encrypting by using one of the plurality of key-encrypting keys; recording means for recording said encrypted digital data and said encrypted contents key on a recording medium; reproducing means for reproducing said encrypted digital data and said encrypted contents key from said recording medium; key decrypting means for decrypting said encrypted contents key to restore said contents key; and contents decrypting means for decrypting said encrypted digital data by using said contents key to obtain said digital data, wherein said encrypted contents key is recorded in a data area on said recording medium, from which data is not output outside, and said encrypted contents key is deleted, while leaving the encrypted digital data, if the encrypted contents key satisfies a predetermined condition.