//*************************************//
//******** created by mamo139 *********//
//*** http://mamo139.altervista.org ***//
//*************************************//


#include <stdio.h> 
#include <string.h> 

int main () { 

    char key[20]="chiave"; 


    FILE * pFile; 
    pFile = fopen ( "input.txt" , "rb" ); 
    long lSize,b,x,keyl=strlen(key); 
    printf("keyl: %d key: %s\n",keyl,key); 
    fseek (pFile , 0 , SEEK_END); 
    lSize = ftell (pFile); 
    fclose (pFile); 

    pFile = fopen ( "input.txt" , "rb" ); 
    char *buf; 

      buf = (char *) malloc(lSize * sizeof(char)); 
  
    b=fread( buf, 1, lSize, pFile); 
    fclose (pFile); 

    FILE * f_out; 
    f_out = fopen ( "output.txt" , "wb" ); 

    for(x=0;x<b;x++){ 
                      buf[x] = buf[x] + key[x%(keyl)]; 

                      
    } 

    fwrite( buf, 1, b, f_out); 
    
    
    fclose (f_out);    
    

    return 0;    
}