backup

uint8_t *caesar_encrypt(uint8_t *plaintext, ushort N)
{
    unsigned int index = 0;
    int length = strlen(plaintext) + 1;
    uint8_t *cipher_text = malloc(length * sizeof(uint8_t));
    while (length >= 0)
    {
        if (isupper(plaintext[index]))
        {
            cipher_text[index] = ((plaintext[index] + N - 65) % 26) + 65;
        }
        else if (islower(plaintext[index]))
        {

            cipher_text[index] = ((plaintext[index] + N - 97) % 26) + 97;
        }
        else if (isdigit(plaintext[index]))
        {
            cipher_text[index] = ((plaintext[index] + N - 48) % 10) + 48;
        }
        else
        {
            cipher_text[index] = plaintext[index];
        }
        index++;
        length--;
    }
    //print_bytes(stdout, cipher_text);

    return cipher_text;
}
uint8_t *caesar_decrypt(uint8_t *ciphertext, ushort N)
{
    unsigned int index = 0;
    int length = strlen(ciphertext) + 1;
    uint8_t *plaintext = malloc(length * sizeof(uint8_t));
    while (length >= 0)
    {
        if (isupper(ciphertext[index]))
        {
            plaintext[index] = (modulo((ciphertext[index] - N - 65), 26)) + 65;
        }
        else if (islower(ciphertext[index]))
        {
            plaintext[index] = (modulo((ciphertext[index] - N - 97), 26)) + 97;
        }
        else if (isdigit(ciphertext[index]))
        {
            plaintext[index] = (modulo((ciphertext[index] - N - 48), 10)) + 48;
        }
        else
        {
            plaintext[index] = ciphertext[index];
        }
        index++;
        length--;
    }
    return plaintext;
}