仿射密码加密与解密简单实现

加密函数: Y=（AX+B）%26
解密函数: X=（A的逆元）*（Y-B）%26

加密程序

#include

int main(){
    FILE *fp = ("fangshe1.txt", "rt");
    FILE *res = fopen("fangshe2.txt", "wt+");
    char ch;
    char r;
    int a = 17, b = 1, m = 26;
    int k = 3;


    if(fp == NULL)
        printf("Cannot open file\n");
    if(res == NULL)
        printf("Cannot open file\n");
    ch = fgetc(fp);
    while(ch != EOF){
        if(ch >= 65 && ch <= 90){
                r = (char) ((a * (ch-65) + b) % m + 65);
                fputc(r, res);
        }
        else if(ch >= 97 && ch <= 122){
                r = (char) ((a * (ch-97) + b) % m + 97);
                fputc(r, res);
        }
        else
                fputc(ch ,res);

        ch = fgetc(fp);
    }
    fclose(fp);
    fclose(res);
}

解密程序

#include

int main(){
    FILE *fp = fopen("fangshe2.txt", "rt");
    FILE *res = fopen("fangshe3.txt", "wt+");
    char ch;
    char r;
    int a = 23, b = 1, m = 26;
    int k = 3;


    if(fp == NULL)
        printf("Cannot open file\n");
    if(res == NULL)
        printf("Cannot open file\n");
    ch = fgetc(fp);
    while(ch != EOF){
        if(ch >= 65 && ch <= 90){
                r = (char) ((a * ((ch-65) - b)) % m + 65);
                fputc(r, res);
        }
        else if(ch >= 97 && ch <= 122){
                r = (char) ((a * ((ch-97) - b)) % m + 97);
                fputc(r, res);
        }
        else
                fputc(ch ,res);

        ch = fgetc(fp);
    }
    fclose(fp);
    fclose(res);
}

a=23是17对于26的乘法逆元, 逆元的计算方法可以看我的另一篇博文点击

待加密文本

GYPQJLRQGPYLJRGQYPL
GQYPRGQPYJRGQYPGY
mj O lezi e hvieq
wpvkn vjg gpf qh yqtnf

待解密文本

ZTWNYGENZWTGYEZNTWG
ZNTWEZNWTYEZNTWZT
xy F grkh r quhrn
lwupo uyz zwi nq tnmoi