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<stdio.h>
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<stdio.h>
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