79 lines
2.0 KiB
Python
79 lines
2.0 KiB
Python
from utils import AlphabetUtils as au
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from utils import CipherUtils as cu
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ALLOWED_KEYS = [1, 3, 5, 7, 9, 11, 15, 17, 19, 21, 23, 25]
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def encrypt_text(cleartext: str, key1: int, key2: int) -> str:
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"""
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Encrypts the given text with the given keys
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:param cleartext: The text to encrypt
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:param key1: The first key. Has to be between 1 and 25 and a coprime to 26
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:param key2: The second key. Has to be between 0 and 26
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:return: The encrypted text
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"""
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# key1 has to be coprime to 26
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if key1 not in ALLOWED_KEYS:
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raise AttributeError
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# key2 has to be between 0 and 25
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if key2 < 0 or key2 > 25:
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raise AttributeError
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cleartext = cu.transform_invalid_chars(cleartext)
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resulting = ''
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for char in cleartext:
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index = au.get_index_of_letter(char)
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new_index = (index * key1 + key2) % 26
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resulting += au.get_letter_at_index(new_index)
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return resulting
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def decrypt_text(ciphertext: str, key1: int, key2: int) -> str:
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"""
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Decrypts the given ciphertext with the given keys
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:param ciphertext: The text to decrypt
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:param key1: The first key. Has to be between 1 and 25 and a coprime to 26
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:param key2: The second key. Has to be between 0 and 26
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:return: The decrypted text
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"""
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# key1 has to be coprime to 26
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if key1 not in ALLOWED_KEYS:
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raise AttributeError
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# key2 has to be between 0 and 25
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if key2 < 0 or key2 > 25:
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raise AttributeError
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decrypt_key1 = _get_key_reverse(key1)
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resulting = ''
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for char in ciphertext:
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index = au.get_index_of_letter(char)
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new_index = ((index - key2) * decrypt_key1) % 26
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resulting += au.get_letter_at_index(new_index)
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return resulting
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def _get_key_reverse(key: int) -> int:
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"""
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Calculates the decryption key (inverse of the original key) based on the following formula:
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s * s' mod 26 = 1
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:param key: The key to reverse
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:return: The decryption key
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"""
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for possibility in ALLOWED_KEYS:
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if (key * possibility) % 26 == 1:
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return possibility
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if __name__ == '__main__':
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print(encrypt_text('BonkRocks', 11, 7))
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print(decrypt_text('sfunmfdnx', 11, 7))
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