rsa.c

一个RSA加解密算法的初级程序

#include "stdio.h"  
#include "string.h"

int e,d=1,n;    

 main(int argc,char *argv[])  
{  

int ip,fai,p=43,q=59,ch1,i=0,j=0,edch,dech=0;  

char *num,*cha,ch,*file={"index.html"};  

FILE *fp,*fp2;    

if (argc<2)  

{  

    printf("paramater error!");  

    exit(0);  

}  

if (argc>3)  

 {  

   file=argv[3];  

 }    


e=iptoint(argv[2]);  

switch (*argv[1])  

{  

case 'e':  

   /* printf("e=%d",e);   */

  if ((fp2=fopen("encode.htm","w+"))==NULL)  

  {  

     printf("can't open file");  

     exit(0);  

  }  

  n=p*q;fai=(p-1)*(q-1);  

  if((fp=fopen(file,"r"))==NULL)  

  {  

     printf("can't open giving file");  

     exit(0);  

  }  

  else  

  {  

    while((ch1=fgetc(fp))!=EOF)  

    {  

         edch=fmod(ch1,e,n);  

         if (edch>0 && edch<10)  

         {     fprintf(fp2,"%s","000"); fprintf(fp2,"%d",edch);  

         }  

         else if (edch<100 && edch>10)  

         {     fprintf(fp2,"%s","00"); fprintf(fp2,"%d",edch);  

         }  

         else if (edch<1000 && edch>100)  

         {     fprintf(fp2,"%s","0"); fprintf(fp2,"%d",edch);  

         }  

         else if (edch<10000 && edch>1000)  

         {     fprintf(fp2,"%d",edch);  

         }  

         else  

               fputc('\n',fp2);  

    }  

  }  

  close(fp);  

  close(fp2);  

  break;  




case 'd':  

 /*  printf("d=%d",e);   */



  if ((fp2=fopen("decode.html","w+"))==NULL)  

  {  

     printf("can't open file");  

     exit(0);  

  }  

  n=p*q;fai=(p-1)*(q-1);  

  while(((d*e)%fai)!=1)  

     d++;  

  if((fp=fopen("encode.htm","r"))==NULL)  

  {  

      printf("can't open file");  

      exit(0);  

  }  

  else  

  {  i=0;  

   /*   printf("e=%d,d=%d,n=%d,",e,d,n);   */

     while((ch=fgetc(fp))!=EOF)  

     {  

        if (i==4)  

        {  

           /* dech=((int)num[0])*1000+((int)num[1])*100+((int)num[2])*10+(int)num[3];   */

           /* printf("yuan=%d,",dech);   */

           dech=fmod(dech,d,n);  

           /* printf("new=%d,",dech);   */

           fprintf(fp2,"%c",dech);  

           i=0;  

           dech=0;  

           /*    */

         }  

         switch (ch)  

         {  

            case '1':dech=dech*10+1;break;

            case '2':dech=dech*10+2;break;  

            case '3':dech=dech*10+3;break;  

            case '4':dech=dech*10+4;break;

            case '5':dech=dech*10+5;break;  

            case '6':dech=dech*10+6;break;  

            case '7':dech=dech*10+7;break;  

            case '8':dech=dech*10+8;break;

            case '9':dech=dech*10+9;break;

            default:dech=dech*10;    

         }  

        /*  printf("dech=%d,",dech);   */

         num[i]=ch;  

         i++;    

     }  

      dech=fmod(dech,d,n);  

      fprintf(fp2,"%c",dech);  

  }  

  close(fp);  

  close(fp2);  

  break;  

default:  

   printf("Usage:code [option]...[Ip Address]...\n");  

   printf("List information about the option\n");  

   printf("e   bind ip address to index.html\n");  

   printf("d   decode from the encodeing file to index2.html");  

}    

}  

int iptoint(ip)  

char *ip;  

{  

int i,ei=0,len;  

int prime=0;    

len=strlen(ip);

for(i=0;i<len;i++) 
{  

      if(ip[i]>'0' && ip[i]<'9')  

      ei=ei+i*((int)ip[i]);  

}  

ei=ei/1000+(ei/100)%10+(ei/10)%10+ei%10;  

/* printf("%d",ei);   */

/* len=ei/2;   */

/* while(prime==0)   */

/* indent: Standard input:2: Error:Unexpected end of file   */

while (((ei % 2)== 0) || ((ei % 3) == 0))  

{   ei=ei+1;  

}  

return(ei);    

}    

int fmod(x, r, p)  

int x,r,p;  

{  

int a,b,c=1;  

a=x;b=r;  

while (b!=0)  

{  

   while ((b%2)==0)  

   {  

      b=b/2;a=(a*a)%p;  

   }  

   b=b-1;c=(a*c)%p;  

}  

return c;  

}