mirror of
https://github.com/TheAlgorithms/Python.git
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95 lines
2.9 KiB
Python
95 lines
2.9 KiB
Python
import sys, random, cryptomath_module as cryptoMath
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SYMBOLS = r""" !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~"""
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def main():
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message = input("Enter message: ")
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key = int(input("Enter key [2000 - 9000]: "))
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mode = input("Encrypt/Decrypt [E/D]: ")
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if mode.lower().startswith("e"):
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mode = "encrypt"
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translated = encryptMessage(key, message)
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elif mode.lower().startswith("d"):
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mode = "decrypt"
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translated = decryptMessage(key, message)
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print("\n%sed text: \n%s" % (mode.title(), translated))
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def getKeyParts(key):
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keyA = key // len(SYMBOLS)
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keyB = key % len(SYMBOLS)
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return (keyA, keyB)
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def checkKeys(keyA, keyB, mode):
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if keyA == 1 and mode == "encrypt":
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sys.exit(
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"The affine cipher becomes weak when key A is set to 1. Choose different key"
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)
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if keyB == 0 and mode == "encrypt":
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sys.exit(
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"The affine cipher becomes weak when key A is set to 1. 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 be between 0 and %s."
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% (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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"Key A %s and the symbol set size %s are not relatively prime. Choose a different key."
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% (keyA, len(SYMBOLS))
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)
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def encryptMessage(key, message):
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"""
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>>> encryptMessage(4545, 'The affine cipher is a type of monoalphabetic 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 = getKeyParts(key)
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checkKeys(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 decryptMessage(key, message):
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"""
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>>> decryptMessage(4545, 'VL}p MM{I}p~{HL}Gp{vp pFsH}pxMpyxIx JHL O}F{~pvuOvF{FuF{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 = getKeyParts(key)
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checkKeys(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 getRandomKey():
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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:
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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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