Patent ID: 7584365

Claim:
A storage system connected to an external device comprising: a first encryption unit; a second encryption unit; a first decryption unit; a second decryption unit; a comparison unit; a counter for counting a number of errors of an encryption in the first encryption unit; and a control unit, wherein the first encryption unit receives a first data from the external device and encrypts the first data; the first decryption unit decrypts the encrypted first data into second data; and the comparison unit compares the second data with the first data, the control unit switches over from the first encryption unit to the second encryption unit, if the first data and the second data are not in agreement in the comparison, so that the second encryption unit encrypts the first data and the second decryption unit decrypts the encrypted first data encrypted by the second encryption unit into third data, the comparison unit compares the third data with the first data, and if the number of errors is greater than a predetermined number, the control unit executes the switch over without finally determining if there is agreement between the first data and the second data.