Rapid modular multiplication method for special domain in SIDH

The invention provides a rapid modular multiplication method for a special domain in SIDH. The method comprises the following steps: setting a cardinal number to express multipliers A and B as an expansion formula taking R as the cardinal number; and converting the calculation of A*B (mod p) into the calculation shown in the description. According to the method, the 2 shift operation is used for multiple times, and then the mathematical formula is used for reducing the large number, so the operation steps are simplified, and the operation speed is greatly increased compared with the prior art. 本发明提出一种SIDH中特殊域快速模乘方法，该方法通过设置基数将乘数A和B表示成以R为基数的展开式；将运算A·B(mod p)转化为计算：本发明多次使用对2移位操作，再利用数学公式将大数化小，简化运算步骤，使得运算速度相较于之前大大提高。