Information security device

A method for use in an information security device that securely and reliably processes predetermined information by performing a power operation d&X over a group defined by a predetermined set and a basic operation that uses elements of the predetermined set, the power operation d&X being the basic operation repeatedly performed d times using an element X, the method comprising:

• an acquisition step for acquiring a value d;
• a main operation step for performing, using a processor, the power operation d&X by performing a window operation and a carry operation based on a window method for each of a plurality of windows, the window operation being performed using the element X and a window value of a corresponding one of the windows, the windows resulting from division of the value d, and each of the windows having a predetermined bit, and
• a processing step of (i) decrypting the predetermined information using a result of the power operation d&X or (ii) adding a digital signature to the predetermined information using result of the power operation d&X,
• wherein with respect to a first window included in the windows, the main operation step uses a random value R to perform the window operation,
• wherein with respect to a second window included in the windows, the main operation step uses a cancellation value S to perform the window operation, and
• wherein the cancellation value S cancels a cumulative factor that is a result of the carry operations performed using the random value R with respect to windows from the first window to the second window.

A non-transitory computer-readable recording medium having recorded therein a computer program for use in an information security device that securely and reliably processes predetermined information by performing a power operation d&X over a group defined by a predetermined set and a basic operation that uses elements of the predetermined set, the power operation d&X being the basic operation repeatedly performed d times using an element X, wherein, when executed, the computer program causes the information security device to perform a method comprising:

• an acquisition step for acquiring a value d;
• a main operation step for performing the power operation d&X by performing a window operation and a carry operation based on a window method for each of a plurality of windows, the window operation being performed using the element X and a window value of a corresponding one of the windows, the windows resulting from division of the value d, and each of the windows having a predetermined bit;
• and
• a processing step of (i) decrypting the predetermined information using a result of the power operation d&X or (ii) adding a digital signature to the predetermined information using a result of the power operation d&X,
• wherein with respect to a first window included in the windows, the main operation step uses a random value R to perform the window operation,
• wherein with respect to a second window included in the windows, the main operation step uses a cancellation value S to perform the window operation, and
• wherein the cancellation value S cancels a cumulative factor that is a result of the carry operations performed using the random value R with respect to windows from the first window to the second window.

An integrated circuit for use in an information security device that securely and reliably processes predetermined information by performing a power operation d&X over a group defined by a predetermined set and a basic operation that uses elements of the predetermined set, the power operation d&X being the basic operation repeatedly performed d times using an element X, the integrated circuit comprising:

• a processor;
• an acquisition unit operable to acquire a value d;
• a main operation unit operable to perform, using the processor, the power operation d&X by performing a window operation and a carry operation based on a window method for each of a plurality of windows, the window operation being performed using the element X and a window value of a corresponding one of the windows, the windows resulting from division of the value d, and each of the windows having a predetermined bit;
• and
• a processing unit operable to (i) decrypt the predetermined information using a result of the power operation d&X or (ii) add a digital signature to the predetermined information using a result of the power operation d&X,
• wherein with respect to a first window included in the windows, the main operation unit uses a random value R to perform the window operation,
• wherein with respect to a second window included in the windows, the main operation unit uses a cancellation value S to perform the window operation, and
• wherein the cancellation value S cancels a cumulative factor that is a result of the carry operations performed using the random value R with respect to windows from the first window to the second window.