仿射加密解密

//功能：仿射加密 密钥：[3][5][9][11][15][17][19][21][23]有逆元的数
例子：pku  c=7,d=3  输出 ：EVN
编辑环境：vc++6.0

include <stdio.h>
int str_len(char *str)
{
 int len = 0;
 while(*(str++))
  len++;
 return len;
}
int main(int argc, char *argv[])
{
 char a[26] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
 char b[26] = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
 char str[50];
 int c,d;
 printf("Please input the words :");
 gets(str);
 printf("Please input the number c [3][5][9][11][15][17][19][21][23] and d:");
 scanf("%d %d",&c,&d);
 int len = str_len(str);

//两层循环，明白排序的重要性了！！
  for(int i = 0;i<len;i++)
  for(int j = 0;j<26;j++)
  {
   if(str[i]==a[j])
    str[i] = b[(c*j+d)%26];
   else
    str[i] = str[i];
  }
  printf("%s\n",str);
 return 0;
}

//解密

#include <stdio.h>
int str_len(char *str)
{
 int len = 0;
 while(*(str++))
  len++;
 return len;
}
int mulny(int k)
{
 int t,i;
 for( i = 0;i<26;i++)
 {
  t=k*i;
  if(t%26==1)
   return i;
 }
}

int main(int argc, char *argv[])
{
 char a[26] = {'a','b','c','d','e','f','g','h','i','j','k','l','m','n','o','p','q','r','s','t','u','v','w','x','y','z'};
 char b[26] = {'A','B','C','D','E','F','G','H','I','J','K','L','M','N','O','P','Q','R','S','T','U','V','W','X','Y','Z'};
 char str[50];
 int c,d;
 printf("Please input the words :");
 gets(str);
 printf("Please input the number c [3][5][9][11][15][17][19][21][23] and d:");
 scanf("%d%d",&c,&d);
 int p = mulny(c);
 int len = str_len(str);
//理解凯撒密码！
 for(int i = 0;i<len;i++)
  for(int j = 0;j<26;j++)
  {
   if(str[i]==b[j])
    str[i] = a[(p*(j-d))%26];//利用数组来完成替换，加密
   else
    str[i] = str[i];
  }
  printf("%s\n",str);
 return 0;
}

 

/*
Today I write two  passages about information security.Those both were that I wrote yesterday and the day before yesterday.Just now, I came back to my room,I took part in a activity about landscape,and I was enjoyable.I was writing a code about "密钥短语" all day.I am so tired now.Last night,the internet was broken off.This night ,I will release my program about "密钥短语" 。

*/