Encryption device and apparatus for encryption/decryption based on the Montgomery method using efficient modular multiplication

摘要

In a modular multiplication circuit which operates under the conditions 0 N 2", 0 ≦ A, B 2N, R = 2ⁿ⁺², a first multiplier performs multiplication between input values A and B. A second multiplier performs multiplication between the output of the first multiplier and [-(N^-1 mod R)], which is decided by set parameters N and R, and outputs M. A third multiplier performs multiplication between the output M and the set parameter N and outputs the product M x N. An adder adds the output of the first multiplier and the output of the third multiplier, and a shift register shifts the sum leftward by n+2 bits. Thus, an output P = (A x B + M x N)/R is produced.