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 sloth(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 moon(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);
  sloth(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: ");
  moon(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!!

How does it work ?

Slothing (Encrypting) 🦥:

~~What is it with these names I pick ?~~ Anyways, the sloth(char *cherry, char *crystal, int *mask) void function takes as parameters three variables:

A pointer to a char array or simply said a string, It's the Cherry.
Another pointer to the Crystal.
And Finally, a pointer to an array of integers The Mask which will be output-ed by the function.

The general idea of it is like this : (we will use a quick example)

Cherry: H e l l o \0.
Crystal: W o r l d \0.
Cherry[0] here is H, or in ASCII 72. And Crystal[0] is W or 87.
Mask[0] in this case is : Cherry[0] - Crystal[0]. which is -15. We then repeat the same steps for each letter on the Crystal.

Why the emphasis on Crystal ? Because we might end up with a case of a Crystal larger than a Cherry. we set the offset to the ASCII value of Crystal[i], okay which to be fair is not the safest option out there, but I'm planning on fixing it sooner or later. In the case of a large Cherry but a small Crystal…it works but now looking at the code, i have no idea why it works the intended way….

Mooning (Decrypting) 🌕:

The function moon(char *cherry, char *crystal, int *mask, int length) works the same way as the sloth function, but in reverse and a small change.

The for loop goes through all the elements of the Mask and reconstructing the Crystal using the reverse equation of the encryption. But when it arrives at the end of the Cherry (here we enter the case of a Cherry smaller than a Crystal). Then we will just assume that Mask[i] is the ASCII code of Crystal[i], and we continue this assumption until the end of the loop.

And voila that's it. Of course there might be some things I will change, but the overall concept is here!