Permalink
Switch branches/tags
Nothing to show
Find file
Fetching contributors…
Cannot retrieve contributors at this time
82 lines (65 sloc) 2.96 KB
# Affine Cipher
# http://inventwithpython.com/hacking (BSD Licensed)
import sys, pyperclip, cryptomath, random
SYMBOLS = """ !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~""" # note the space at the front
def main():
myMessage = """"A computer would deserve to be called intelligent if it could deceive a human into believing that it was human." -Alan Turing"""
myKey = 2023
myMode = 'encrypt' # set to 'encrypt' or 'decrypt'
if myMode == 'encrypt':
translated = encryptMessage(myKey, myMessage)
elif myMode == 'decrypt':
translated = decryptMessage(myKey, myMessage)
print('Key: %s' % (myKey))
print('%sed text:' % (myMode.title()))
print(translated)
pyperclip.copy(translated)
print('Full %sed text copied to clipboard.' % (myMode))
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 incredibly weak when key A is set to 1. Choose a different key.')
if keyB == 0 and mode == 'encrypt':
sys.exit('The affine cipher becomes incredibly weak when key B is set to 0. Choose a 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):
keyA, keyB = getKeyParts(key)
checkKeys(keyA, keyB, 'encrypt')
ciphertext = ''
for symbol in message:
if symbol in SYMBOLS:
# encrypt this symbol
symIndex = SYMBOLS.find(symbol)
ciphertext += SYMBOLS[(symIndex * keyA + keyB) % len(SYMBOLS)]
else:
ciphertext += symbol # just append this symbol unencrypted
return ciphertext
def decryptMessage(key, message):
keyA, keyB = getKeyParts(key)
checkKeys(keyA, keyB, 'decrypt')
plaintext = ''
modInverseOfKeyA = cryptomath.findModInverse(keyA, len(SYMBOLS))
for symbol in message:
if symbol in SYMBOLS:
# decrypt this symbol
symIndex = SYMBOLS.find(symbol)
plaintext += SYMBOLS[(symIndex - keyB) * modInverseOfKeyA % len(SYMBOLS)]
else:
plaintext += symbol # just append this symbol undecrypted
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 affineCipher.py is run (instead of imported as a module) call
# the main() function.
if __name__ == '__main__':
main()