Data processing device and data processing method

A data processing device which reads and decrypts encrypted data sets and encrypted key data sets stored in a storage medium, the encrypted data sets being obtained by dividing to-be-stored data into a plurality of divided data sets and then encrypting at least some of the divided data sets for decryption by respectively different key data sets, the encrypted key data sets being obtained by encrypting the key data sets for decryption by a common key data set, the data processing device comprising:

• a read-control portion for controlling reading of each said encrypted data set and each said encrypted key data set;
• a decryption portion for decrypting the encrypted data set and the encrypted key data set that have been read under the control of the read-control portion;
• and
• a key-data retention portion that retains the common key data set, and one of the key data sets decrypted from the encrypted key data set by the decryption portion,
• wherein the decryption portion is configured so as to decrypt the encrypted data set and the encrypted key data set based on one of the key data sets or the common key data set retained in the key-data retention portion.

A data processing method, in which encrypted data sets and encrypted key data sets stored in a storage medium are read and decrypted, the encrypted data sets being obtained by dividing to-be-stored data into a plurality of divided data sets and then encrypting at least some of the divided data sets for decryption by respectively different key data sets, each of the encrypted key data sets being obtained by encrypting each said key data set for decryption by any one of the other key data sets, the data processing method comprising the steps of:

• (a) reading one of the encrypted data sets and one of the encrypted key data sets;
• and
• (b) decrypting said one encrypted data set and said one encrypted key data set that have been read in the step (a), and then making a key-data retention portion retain one of the key data sets that has been decrypted from said one encrypted key data set;
• wherein in the step (b), said one encrypted data set and said one encrypted key data set are decrypted based on one of the key data sets that has already been retained in the key-data retention portion.

A data processing method, in which encrypted data sets and encrypted key data sets stored in a storage medium are read and decrypted, the encrypted data sets being obtained by dividing to-be-stored data into a plurality of divided data sets and then encrypting at least some of the divided data sets for decryption by respectively different key data sets, the encrypted key data sets being obtained by encrypting the key data sets for decryption by a common key data set, the data processing method comprising the steps of:

• (a) reading one of the encrypted data sets and one of the encrypted key data sets;
• and
• (b) decrypting said one encrypted data set and said one encrypted key data set that have been read in the step (a), and then making a key-data retention portion retain one of the key data sets that has been decrypted from said one encrypted key data set;
• wherein in the step (b), said one encrypted data set and said one encrypted key data set are decrypted based on one of the key data sets or the common key data set that has already been retained in the key-data retention portion.