Patent ID: 8577022

Claim:
A data processing apparatus including means for encrypting subject data in plain text by using a predetermined algorithm and a predetermined key to render it as encrypted data, a recording medium for recording the encrypted data, and means for decrypting the encrypted data read from the recording medium by using the algorithm and key used when encrypting the encrypted data to render it as the subject data, comprising: cutting means for cutting the subject data by a predetermined number of bits into multiple pieces of plain text cut data and also cutting the encrypted data into multiple pieces of encrypted cut data by the same number of bits by which the encrypted data is cut when encrypted; encrypting and decrypting means for encrypting the plain text cut data with the key and the algorithm changing in predetermined timing to render it as the encrypted cut data and decrypting the encrypted cut data with the key and algorithm used when encrypting the encrypted cut data to render it as the plain text cut data, the means performing the encryption or the decryption per standard number of bits as a standard; reading and writing means for recording on the recording medium the encrypted data having the encrypted cut data encrypted by the encrypting and decrypting means connected as one and reading the encrypted data recorded on the recording medium from the recording medium; connecting means for connecting the decrypted plain text cut data to render it as the subject data; and specific information recording means for recording specific information for identifying the algorithm used when encrypting the subject data on a predetermined recording medium by associating it with the encrypted data, and wherein: the cutting means cuts the subject data by the number of bits shorter than the standard number of bits; and having mixing means provided for the sake of matching the number of bits of the plain text cut data with the standard number of bits by including dummy data irrelevant to the subject data in the plain text cut data; and when decrypting the encrypted cut data, the encrypting and decrypting means reads the specific information associated with the encrypted data from the specific information recording means, and performs the decryption with the key and the algorithm identified based on the specific information.