密钥短语密码体制之c语言实现.txt

c语言的一些常见的算法以及思考和改进的文章,写的很不错,花费了很大的精力从网络了搜罗的,希望大家喜欢.

密钥短语密码体制之C语言实现[原创] 
#define M 80
#define N 27

＃i nclude <ctype.h>

void daihuan(char m[],char k[],char c[])
{
   int i,t;
   for(i=0;m[i];i++)
     if(isalpha(m[i]))
     {
          t=(m[i]-'A')%32;
          c[i]=k[t];
     }
     else
          c[i]=m[i];
   c[i]=0;
}

int position(char ch,char string[])
{
   int i;
   for(i=0;string[i];i++)
     if(ch==string[i])
       break;
   if(string[i])
      return i;
   return -1;
}

void jiemi(char c[],char k[],char m[])
{
   int i,t;
   for(i=0;c[i];i++)
     if(isalpha(c[i]))
     {
       if(position(c[i],k)!=-1)
           m[i]='a'+position(c[i],k);
     }
     else
       m[i]=c[i];
   m[i]=0;
}

void delete(char string[])
{/*delete the space and repeated letters*/
   int i,j,pos=0;
   char t[N];
   strcpy(t,string);
   for(i=0;t[i];i++)
   {
     for(j=0;j<i;j++)
       if(t[j]==t[i])
             break;
     if(j>=i&&isalpha(t[i]))
          string[pos++]=t[i];
   }
   string[pos]=0;
}

void expand(char string[])
{
  int i,j,k;
  for(i=0;string[i]!='\0';i++)
    string[i]=toupper(string[i]);
  for(j='A';j<='Z';j++)
  {
    for(k=0;k<i;k++)
      if(string[k]==j)
           break;
    if(k>=i)
      string[i++]=j;
  }
  string[26]='\0';
}

void main()
{
   char m[M],k[N],c[M],temp[M];
   printf("\nPlease input the mingwen:\n");
   gets(m);
   printf("\nPlease input the key:\n");
   gets(k);
   delete(k);
   expand(k);
   daihuan(m,k,c);
   jiemi(c,k,temp);
   printf("\The mingwen is:\n%s\nand the key is:\n%s\nand the cryptograph is:\n%s\nand the restored string is:\n%s\n",m,k,c,temp);
}