[密码学--RSA的加解密]

RSA算法详解及C语言实现

#include <stdio.h>
int candp( int a, int b, int c )
{
    int r = 1;
    b = b + 1;
    while ( b != 1 )
    {
        r   = r * a;
        r   = r % c;
        b--;
    }
    printf( "%d\n", r );
    return(r);
}


void main()
{
    int p, q, e, d, m, n, t, c, r;
    char    s;
    printf( "please input the p,q: " );
    scanf( "%d%d", &p, &q );
    n = p * q;
    printf( "the n is %3d\n", n );
    t = (p - 1) * (q - 1);
    printf( "the t is %3d\n", t );
    printf( "please input the e: " );
    scanf( "%d", &e );
    if ( e < 1 || e > t )
    {
        printf( "e is error,please input again: " );
        scanf( "%d", &e );
    }
    d = 1;
    while ( ( (e * d) % t) != 1 )     
        d++;
    printf( "then caculate out that the d is %d\n", d );
    printf( "the cipher please input 1\n" );
    printf( "the plain please input 2\n" );
    scanf( "%d", &r );
    switch ( r )
    {
    case 1: printf( "input the m: " );      /*输入要加密的明文数字*/
        scanf( "%d", &m );
        c = candp( m, e, n );/*（加密的明文数字，加密指数，欧拉数）*/
        printf( "the cipher is %d\n", c ); break;
    case 2: printf( "input the c: " );      /*输入要解密的密文数字*/
        scanf( "%d", &c );
        m = candp( c, d, n );/*（需解密的密文，*/
        printf( "the cipher is %d\n", m ); break;
    }
    getchar();
}