Krypto_Grundlagen/chapter_one/Verschiebe-Chiffre.py

def encrypt_text(cleartext: str = 'Bitcoin', incrementation: int = 13):
    """
    This method encrypts a text by shifting each letter by the value of incrementation

    :param cleartext: The secret message to encrypt
    :param incrementation: How much the letters should be shifted
    :return: Encrypted text
    """
    return shift_text(cleartext, (incrementation % 26))  # '%' to repeat after 26 with 0


def decrypt_text(encrypted_text: str = 'Ovgpbva', incrementation: int = 13):
    """
    This method decrypts a text by shifting each letter by the value of incrementation

    :param encrypted_text: The encrypted secret message to decrypt
    :param incrementation: How much the letters should be shifted
    :return: Decrypted text
    """
    return shift_text(encrypted_text, 26 - (incrementation % 26))  # '%' to repeat after 26 with 0


def shift_text(cleartext: str, incrementation: int):
    """
    This method shifts every letter of a string by the value of incrementation
    :param cleartext: The string to be shifted
    :param incrementation: How much the letters should be shifted
    :return: Shifted text
    """
    shifted_text = ''

    for char in cleartext:
        shifted_text += increment_char(char, incrementation)

    return shifted_text


def increment_char(char, incrementation: int = 1):
    """
    This method shifts one char by the value of incrementation

    :param char: Char to be shifted
    :param incrementation: How much the char should be shifted
    :return: Shifted letter
    """
    # converting character to byte
    char_in_bytes = bytes(char, 'utf-8')[0]
    if char_in_bytes + incrementation >= 91 and char_in_bytes < 91 \
            or char_in_bytes + incrementation >= 123:  # z -> 122 | 90 -> Z so go backwards
        new_char_in_bytes = bytes([char_in_bytes - (26 - incrementation)])
    else:
        new_char_in_bytes = bytes([char_in_bytes + incrementation])

    return str(new_char_in_bytes)[2]


def brute_force_example(cleartext: str = 'Bitcoin', incrementation: int = 7):
    """
    This is an example of how to bruteforce an encrypted text. (Encrypted with Letter-Shifting)

    :param cleartext: The secret message to encrypt and decrypt during bruteforcing
    :param incrementation: How much the letters should be shifted
    """
    encrypted_text = encrypt_text(cleartext, incrementation=incrementation)

    for x in range(26):
        if cleartext == decrypt_text(encrypted_text, incrementation=x):
            print(f'Text was shifted by {x} letters.')


if __name__ == '__main__':
    print(encrypt_text())
    print(decrypt_text())

    brute_force_example()