Reviving Caesar with a Cherry-flavored Crystal

What ?…

That is probably your reaction reading this title, and no, this isn’t a randomly generated sentence, but rather a simple encryption algorithm I recently made (Actually the first encryption algorithm i make at all!!). Meet Cherry-Crystal Encryption.

Okay so, what is this all about ?

This encryption Algorithm that we will call CCE for short, takes inspiration from the Caesar cipher which needn’t an introduction (you can find great explanations online). But what about mine you might ask ?

It’s actually pretty simple. We start with a Cherry or a Visible phrase, or a Decoy, that we will share to people who we don’t want to know the secret phrase..
Then we ask the user to enter their Crystal, invisible phrase or secret.
The program then outputs an array of Integers called the Mask, or the Shift. That is, the shift required to go from cherry_i to crystal_i.
Finally, we use both the Cherry and Mask to get the Crystal, a single missing number or letter from both of them can and will output rubbish content.

The Code :

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

void encrypt(char cherry[], char crystal[], int mask[]) {
  int i;
  for (i = 0; i < strlen(cherry) - 1; i++) {
    mask[i] = cherry[i] - crystal[i];
  }
  for (i = strlen(cherry) - 1; i < strlen(crystal) - 1; i++) {
    mask[i] = crystal[i];
  }
}
void decrypt(char cherry[], char crystal[], int mask[], int length) {
  int i, end = 1;
  for (i = 0; i < length; i++) {
    if (i == strlen(cherry) - 1 || end == 0) {
      crystal[i] = mask[i];
      end = 0;
    } else {
      crystal[i] = cherry[i] - mask[i];
    }
  }
}
int main(int argc, char *argv[]) {
  const int size = 1028;
  char cherry[size], cherry2[size], crystal[size], crystal2[size];
  int mask[size], mask2[size], i;
  int length = 0;
  puts("Enter the Cherry: ");
  fgets(cherry, size, stdin);
  puts("Enter the Crystal: ");
  fgets(crystal, size, stdin);
  encrypt(cherry, crystal, mask);
  for (i = 0; i < strlen(crystal) - 1; i++) {
    printf("%d ", mask[i]);
    length++;
  }
  printf("\nYour mask is : %d characters long", length);
  puts("\n===Decryption: ===\n");
  puts("Enter the Cherry: ");
  fgets(cherry2, size, stdin);
  puts("Enter the size of the Mask: ");
  scanf("%d", &length);
  puts("Enter the mask: ");
  for (i = 0; i < length; i++) {
    scanf("%d", &mask2[i]);
  }
  puts("The Crystal is: ");
  decrypt(cherry2, crystal2, mask2, length);
  puts(crystal2);
  return 0;
}

The program has been tested both on Alpine OS with Musl libc (thanks Kin) and on OpenBSD 7.5-current. In the close future I will make a git repo as i’m planning to upgrade it and just make it better overall, who knows, maybe i will make a library out of it!!