iframe-proxy | Sunbelt Computer Software

History

77 lines (68 loc) · 2.85 KB

Raw

from __future__ import print_function

import sys, random, cryptomath_module as cryptoMath

SYMBOLS = r""" !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~"""

def main():

message = input('Enter message: ')

key = int(input('Enter key [2000 - 9000]: '))

mode = input('Encrypt/Decrypt [E/D]: ')

if mode.lower().startswith('e'):

mode = 'encrypt'

translated = encryptMessage(key, message)

elif mode.lower().startswith('d'):

mode = 'decrypt'

translated = decryptMessage(key, message)

print('\n%sed text: \n%s' % (mode.title(), translated))

def getKeyParts(key):

keyA = key // len(SYMBOLS)

keyB = key % len(SYMBOLS)

return (keyA, keyB)

def checkKeys(keyA, keyB, mode):

if keyA == 1 and mode == 'encrypt':

sys.exit('The affine cipher becomes weak when key A is set to 1. Choose different key')

if keyB == 0 and mode == 'encrypt':

sys.exit('The affine cipher becomes weak when key A is set to 1. Choose different key')

if keyA < 0 or keyB < 0 or keyB > len(SYMBOLS) - 1:

sys.exit('Key A must be greater than 0 and key B must be between 0 and %s.' % (len(SYMBOLS) - 1))

if cryptoMath.gcd(keyA, len(SYMBOLS)) != 1:

sys.exit('Key A %s and the symbol set size %s are not relatively prime. Choose a different key.' % (keyA, len(SYMBOLS)))

def encryptMessage(key, message):

'''

>>> encryptMessage(4545, 'The affine cipher is a type of monoalphabetic substitution cipher.')

'VL}p MM{I}p~{HL}Gp{vp pFsH}pxMpyxIx JHL O}F{~pvuOvF{FuF{xIp~{HL}Gi'

'''

keyA, keyB = getKeyParts(key)

checkKeys(keyA, keyB, 'encrypt')

cipherText = ''

for symbol in message:

if symbol in SYMBOLS:

symIndex = SYMBOLS.find(symbol)

cipherText += SYMBOLS[(symIndex * keyA + keyB) % len(SYMBOLS)]

else:

cipherText += symbol

return cipherText

def decryptMessage(key, message):

'''

>>> decryptMessage(4545, 'VL}p MM{I}p~{HL}Gp{vp pFsH}pxMpyxIx JHL O}F{~pvuOvF{FuF{xIp~{HL}Gi')

'The affine cipher is a type of monoalphabetic substitution cipher.'

'''

keyA, keyB = getKeyParts(key)

checkKeys(keyA, keyB, 'decrypt')

plainText = ''

modInverseOfkeyA = cryptoMath.findModInverse(keyA, len(SYMBOLS))

for symbol in message:

if symbol in SYMBOLS:

symIndex = SYMBOLS.find(symbol)

plainText += SYMBOLS[(symIndex - keyB) * modInverseOfkeyA % len(SYMBOLS)]

else:

plainText += symbol

return plainText

def getRandomKey():

while True:

keyA = random.randint(2, len(SYMBOLS))

keyB = random.randint(2, len(SYMBOLS))

if cryptoMath.gcd(keyA, len(SYMBOLS)) == 1:

return keyA * len(SYMBOLS) + keyB

if __name__ == '__main__':

import doctest

doctest.testmod()

main()

Sunbelt Computer Software

PL/B Language Development and Support

Navigation Menu

Uh oh!

Sunbelt Computer Software

PL/B Language Development and Support

Uh oh!

FilesExpand file tree

affine_cipher.py

Latest commit

History

affine_cipher.py

File metadata and controls