Modulo reduction method using a precomputed table

A modulo reduction method using a precomputed table to increase a reduction speed during the execution of ordinary operational processes using computers and comprises a first step which searches out with an index of an upper log2 t (t≧1) bit number and adds the value stored in a table to a lower n(n≧512) bit number; a second step, which if the result, obtained from the addition of said lower n bit number to the number searched out from the table at said first step, produces an overflow (1 bit), eliminates said overflow and finishes the execution of an operation; and a third step, which if said overlow does not occur at said second step, addsN on a modulo N to the result obtained from said first step and finishes the execution of the operation.