PURPOSE: To ensure safety and to enable the high speed processing by using a specific multiplier as a multiplier for performing power-multiplying operation in the exponential multiplying method.

CONSTITUTION: In the RSA cryptography, an equation for implementing the ciphering of a plain sentence M is expressed as Me=Cmodn, and an equation for implementing the deciphering of a cryptographic sentence C is as Cd= Mmodn. Where, M: message, C: cryptographic sentence, e: open key, d: secret key, n: p q, p, q: large prime numbers (secret). Further, while generally the RSA cryptograpy IS often selected to be 2<e<<d, there is no restriction to (e) and (d) in the case of shortening the calculating time. In the RSA cryptographic system of the system-constituting principle drawing, M: plain sentence (message), e: open key, Rx-y: open key n [R, x (number of figures for n), y is non-small integer], C: cryptographic sentence, d: secret key. When the euations Me=Cmodn and Cd=Cmodn are implemented, the exponential multiplying method is used.