仿射变换加密

根据公式c = Ea, b(m) ☰ a * m + b (mod 26);

如果已知a, b, 加密非常简单，代码如下：

#include <bits/stdc++.h>
using namespace std;
int a, b;
void Input()
{
    int p, val;
    char key;
    char key_2[1010];
    cout << "请输入a, b的值（中间以空格分开）" << endl;
    scanf("%d %d", &a, &b);
    cout << "一次输入一个字符请输入 1 否则请输入 2" << endl;
    scanf("%d", &p);
    if(p == 1)
    {
        getchar();
        while(scanf("%c", &key) != EOF)
        {
            if(key != '\n')
            {
             val = ((key - 'A') * a + b) % 26;
            key = 'A' + val;
            cout << "val = " << val << " key =  " << key << endl;
            }
        }
    }
    else
        {
            getchar();
            gets(key_2);
            int len = strlen(key_2);
            for(int i = 0; i < len; ++i)
            {
                if(key_2[i] >= 'A' && key_2[i] <= 'Z')
                {
                 val = ((key_2[i] - 'A') * a + b) % 26;
                 key_2[i] = val + 'A';
                }
            }
            cout << key_2 << endl;
        }

}
int main()
{
    Input();
}