Abstract: An encryption apparatus provided with a Feistel type encryption algorithm includes a function operation unit that operates a non-linear function, and changing unit configured to supply the function operation unit with random data unrelated to an encryption operation result. In this way, a countermeasure can be taken against a DPA attack following the end of an operation by the encryption operation apparatus provided with the Feistel type encryption algorithm.

Abstract: A modular multiplication apparatus comprises a calculation unit which comprises processing units including a multiplier-adder unit and performs a modular multiplication by carrying out pipeline processes by the processing units; and a calculator configured to, before a first pipeline process, carry out a predetermined calculation for a processing result of one of the processing units in a pipeline process immediately before the first pipeline process, and when the first pipeline processes supply a calculation result of the predetermined calculation to a processing unit at an initial stage of the first pipeline process.

Abstract: A modular exponentiation calculation apparatus obtains a first RNS representation of a value Cpdp×B mod p based on an RNS representation of a remainder value Cp=C mod p and a remainder value dp=d mod (p−1), obtains a second RNS representation of a value Cqdq×B mod q based on an RNS representation of a remainder value Cq=C mod q and a remainder value dq=d mod (p−1), obtains a third RNS representation of an integer m′ congruent with Cd mod (p×q) based on both the first and second RNS representations, and obtains m=Cd mod (p×q) based on a value of the integer m′ obtained by converting the third RNS representation into a binary representation.