XOR encryptation looks cool as well

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

#define ENCRYPT(a,b) (encrypt_decrypt (a, b))
#define DECRYPT(a,b) (encrypt_decrypt (a, b))


signed char *
encrypt_decrypt (char *str, char *key)
{
 char *crp_str, *addr;
 crp_str = addr = (char *) malloc (strlen (str));
 if (crp_str == 0)
  return (char *)-1;   
 for (; *str;
  str++, key++, crp_str++)
  *crp_str = *str ^ *key;
 *crp_str = '\0';
 return addr;
}

int 
main (void)
{
 char *str;
 str = ENCRYPT ("Hello World", "Im nice guy"); 
 printf ("%s\n", DECRYPT (str, "Im nice guy")); 
 return 0;
}