mirror of
https://github.com/TheAlgorithms/Python.git
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35eefac359
this will fix code from randomly throwing `SystemExit: The affine cipher becomes weak when key B is set to 0. Choose different key` exception.
106 lines
3.2 KiB
Python
106 lines
3.2 KiB
Python
import random
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import sys
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from . import cryptomath_module as cryptomath
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SYMBOLS = (
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r""" !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`"""
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r"""abcdefghijklmnopqrstuvwxyz{|}~"""
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)
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def main():
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"""
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>>> key = get_random_key()
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>>> msg = "This is a test!"
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>>> decrypt_message(key, encrypt_message(key, msg)) == msg
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True
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"""
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message = input("Enter message: ").strip()
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key = int(input("Enter key [2000 - 9000]: ").strip())
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mode = input("Encrypt/Decrypt [E/D]: ").strip().lower()
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if mode.startswith("e"):
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mode = "encrypt"
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translated = encrypt_message(key, message)
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elif mode.startswith("d"):
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mode = "decrypt"
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translated = decrypt_message(key, message)
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print(f"\n{mode.title()}ed text: \n{translated}")
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def check_keys(keyA, keyB, mode):
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if mode == "encrypt":
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if keyA == 1:
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sys.exit(
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"The affine cipher becomes weak when key "
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"A is set to 1. Choose different key"
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)
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if keyB == 0:
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sys.exit(
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"The affine cipher becomes weak when key "
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"B is set to 0. Choose different key"
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)
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if keyA < 0 or keyB < 0 or keyB > len(SYMBOLS) - 1:
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sys.exit(
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"Key A must be greater than 0 and key B must "
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f"be between 0 and {len(SYMBOLS) - 1}."
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)
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if cryptomath.gcd(keyA, len(SYMBOLS)) != 1:
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sys.exit(
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f"Key A {keyA} and the symbol set size {len(SYMBOLS)} "
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"are not relatively prime. Choose a different key."
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)
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def encrypt_message(key: int, message: str) -> str:
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"""
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>>> encrypt_message(4545, 'The affine cipher is a type of monoalphabetic '
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... 'substitution cipher.')
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'VL}p MM{I}p~{HL}Gp{vp pFsH}pxMpyxIx JHL O}F{~pvuOvF{FuF{xIp~{HL}Gi'
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"""
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keyA, keyB = divmod(key, len(SYMBOLS))
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check_keys(keyA, keyB, "encrypt")
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cipherText = ""
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for symbol in message:
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if symbol in SYMBOLS:
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symIndex = SYMBOLS.find(symbol)
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cipherText += SYMBOLS[(symIndex * keyA + keyB) % len(SYMBOLS)]
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else:
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cipherText += symbol
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return cipherText
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def decrypt_message(key: int, message: str) -> str:
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"""
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>>> decrypt_message(4545, 'VL}p MM{I}p~{HL}Gp{vp pFsH}pxMpyxIx JHL O}F{~pvuOvF{FuF'
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... '{xIp~{HL}Gi')
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'The affine cipher is a type of monoalphabetic substitution cipher.'
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"""
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keyA, keyB = divmod(key, len(SYMBOLS))
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check_keys(keyA, keyB, "decrypt")
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plainText = ""
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modInverseOfkeyA = cryptomath.findModInverse(keyA, len(SYMBOLS))
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for symbol in message:
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if symbol in SYMBOLS:
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symIndex = SYMBOLS.find(symbol)
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plainText += SYMBOLS[(symIndex - keyB) * modInverseOfkeyA % len(SYMBOLS)]
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else:
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plainText += symbol
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return plainText
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def get_random_key():
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while True:
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keyA = random.randint(2, len(SYMBOLS))
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keyB = random.randint(2, len(SYMBOLS))
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if cryptomath.gcd(keyA, len(SYMBOLS)) == 1 and keyB % len(SYMBOLS) != 0:
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return keyA * len(SYMBOLS) + keyB
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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# main()
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