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583a614fef
* Deleted greatest_common_divisor def from many files and instead imported the method from Maths folder * Deleted greatest_common_divisor def from many files and instead imported the method from Maths folder, also fixed comments * [pre-commit.ci] auto fixes from pre-commit.com hooks for more information, see https://pre-commit.ci * Deleted greatest_common_divisor def from many files and instead imported the method from Maths folder, also fixed comments * Imports organized * recursive gcd function implementation rolledback * more gcd duplicates removed * more gcd duplicates removed * Update maths/carmichael_number.py * updated files * moved a file to another location --------- Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com> Co-authored-by: Tianyi Zheng <tianyizheng02@gmail.com>
110 lines
3.4 KiB
Python
110 lines
3.4 KiB
Python
import random
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import sys
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from maths.greatest_common_divisor import gcd_by_iterative
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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 check_keys(key_a: int, key_b: int, mode: str) -> None:
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if mode == "encrypt":
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if key_a == 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 key_b == 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 key_a < 0 or key_b < 0 or key_b > 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 gcd_by_iterative(key_a, len(SYMBOLS)) != 1:
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sys.exit(
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f"Key A {key_a} 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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key_a, key_b = divmod(key, len(SYMBOLS))
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check_keys(key_a, key_b, "encrypt")
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cipher_text = ""
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for symbol in message:
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if symbol in SYMBOLS:
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sym_index = SYMBOLS.find(symbol)
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cipher_text += SYMBOLS[(sym_index * key_a + key_b) % len(SYMBOLS)]
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else:
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cipher_text += symbol
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return cipher_text
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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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key_a, key_b = divmod(key, len(SYMBOLS))
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check_keys(key_a, key_b, "decrypt")
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plain_text = ""
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mod_inverse_of_key_a = cryptomath.find_mod_inverse(key_a, len(SYMBOLS))
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for symbol in message:
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if symbol in SYMBOLS:
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sym_index = SYMBOLS.find(symbol)
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plain_text += SYMBOLS[
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(sym_index - key_b) * mod_inverse_of_key_a % len(SYMBOLS)
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]
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else:
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plain_text += symbol
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return plain_text
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def get_random_key() -> int:
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while True:
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key_b = random.randint(2, len(SYMBOLS))
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key_b = random.randint(2, len(SYMBOLS))
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if gcd_by_iterative(key_b, len(SYMBOLS)) == 1 and key_b % len(SYMBOLS) != 0:
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return key_b * len(SYMBOLS) + key_b
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def main() -> None:
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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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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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# main()
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