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https://github.com/TheAlgorithms/Python.git
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77 lines
2.8 KiB
Python
77 lines
2.8 KiB
Python
import sys, random, cryptomath_module as cryptoMath
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SYMBOLS = """ !"#$%&'()*+,-./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('The affine cipher becomes weak when key A is set to 1. Choose different key')
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if keyB == 0 and mode == 'encrypt':
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sys.exit('The affine cipher becomes weak when key A is set to 1. Choose different key')
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if keyA < 0 or keyB < 0 or keyB > len(SYMBOLS) - 1:
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sys.exit('Key A must be greater than 0 and key B must be between 0 and %s.' % (len(SYMBOLS) - 1))
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if cryptoMath.gcd(keyA, len(SYMBOLS)) != 1:
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sys.exit('Key A %s and the symbol set size %s are not relatively prime. Choose a different key.' % (keyA, len(SYMBOLS)))
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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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