Apparatus, method, and computer program product for recording content

A method to play back content that is recorded on a recording medium and that is encrypted by a first cryptographic key, the first cryptographic key being encrypted by using a second cryptographic key in a key storing unit and being recorded on the recording medium, the method comprising:

• decrypting encrypted first cryptographic key by using the second cryptographic key;
• decrypting encrypted content by using the first cryptographic key;
• playing back decrypted content;
• verifying whether a content certificate exists in the recording medium, the content certificate including a certificate type registering a content type indicative of a record type of the content on the recording medium, a hash value based on information of a portion of the content, and a signature created for the certificate type and the hash value by using a private key that corresponds to a public key in the key storing unit;
• determining, when the content certificate exists in the recording medium, whether a combination of the certificate type of the content certificate recorded on the recording medium and a medium type of the recording medium is a proper combination;
• verifying, when the combination of the certificate type and the medium type of the recording medium is the proper combination, whether the hash value included in the content certificate matches a hash value calculated from the content;
• and
• verifying, when the content certificate does not exist in the recording medium, whether, at the time of playback of the content, a digital watermark is embedded in the content, wherein
• the playing back includes continuing to play back the content when the hash value included in the content certificate matches the hash value calculated from the content and aborting playback of the content when the combination of the certificate type and the medium type of the recording medium is not the proper combination, when the hash value included in the content certificate does not match the hash value calculated from the content, or when the digital watermark is embedded in the content.

A non-transitory computer-readable recording medium encoded with instructions, which when executed by a computer, causes the computer to execute a method to play back content that is recorded on a recording medium and that is encrypted by a first cryptographic key, the first cryptographic key being encrypted by using a second cryptographic key in a key storing unit and being recorded on the recording medium, the method comprising:

• decrypting encrypted first cryptographic key by using the second cryptographic key;
• decrypting encrypted content by using the first cryptographic key;
• playing back decrypted content;
• verifying whether a content certificate exists in the recording medium, the content certificate including a certificate type registering a content type indicative of a record type of the content on the recording medium, a hash value based on information of a portion of the content, and a signature created for the certificate type and the hash value by using a private key that corresponds to a public key in the key storing unit;
• determining, when the content certificate exists in the recording medium, whether a combination of the certificate type of the content certificate recorded on the recording medium and a medium type of the recording medium is a proper combination;
• verifying, when the combination of the certificate type and the medium type of the recording medium is the proper combination, whether the hash value included in the content certificate matches a hash value calculated from the content;
• and
• verifying, when the content certificate does not exist in the recording medium, whether, at the time of playback of the content, a digital watermark is embedded in the content, wherein
• the playing back includes continuing to play back the content when the hash value included in the content certificate matches the hash value calculated from the content and aborting playback of the content when the combination of the certificate type and the medium type of the recording medium is not the proper combination, when the hash value included in the content certificate does not match the hash value calculated from the content, or when the digital watermark is embedded in the content.