Question

My C program is supposed to make a random key the same length of clear_text string and then use the random key to encrypt clear_text, but I can’t get it to work.

A wΝΗ 1 #include <stdio.h> 2 #include<stdlib.h> 3 #include<time.h> 4 char* make_rand_key(int length, char* key); 5 void encrypt(); 7- int main() { 8 encrypt(); 9 }

Answer 1

The reason it failed is
- clear_text, key, encrypted are all declared as pointers. You have not assigned memory to it. You should either declare them as clear_text[20] etc or char *clear_text = malloc(sizeof(char)*20); I have given them a size while declaring.

- The encrypted string did not end with \0 in your code. Fixed that.

The fixed code is given below

#include <stdio.h>
#include <stdlib.h>
#include <time.h>
char* make_rand_key(int length, char* key);
void encrypt();
int main(){
   encrypt();
}

char* make_rand_key(int length, char* key){
   int range = 78;
   int max = 48;
   char c = 'a';
   int i;
   srand(time(NULL));
   for(i = 0; i < length; i++){
       c = rand() % range + max;
       key[i] = c;
   }
   key[i] = '\0';
   return key;
}

void encrypt(){
   char clear_text[30] = "Hello everybody";
   int length = 0;
   while(clear_text[length] != '\0')
       length++;
   char key[30];
   char encrypted[30];
   int x;
   for(x = 0; x < length; x++){
       encrypted[x] = clear_text[x] ^ key[x];
   }
   encrypted[length] = '\0';
   printf("%s\n", encrypted);
}