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The affine cipher is the multiplicative cipher, which is then encrypted by the Caesar cipher on top of that. The affine cipher needs two keys: one for the multiplicative cipher multiplication and the other for the Caesar cipher addition. For the affine cipher program, we will use a single integer for the key. We will use some simple math to split this key into the two keys, which we will call Key A and Key B.Its working needs to explained . If you want me to explain how it works ,let me know in the comments and I'll explain it .
First of all we need to make a python file and save it as cryptomath.We will need to call this later in our program.
now create a new folder and save the cryptomath and affine cipher there.
NOTE :- both the python file should be in the same folder or it would be diificult to call the crpytomath module later in our cipher.
SOURCE CODE (Cryptomath) :-
source- www.inventwithpython.com
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# Cryptomath Module
def gcd(a, b):
# Return the GCD of a and b using Euclid's Algorithm
while a != 0:
a, b = b % a, a
return b
def findModInverse(a, m):
# Returns the modular inverse of a % m, which is
# the number x such that a*x % m = 1
if gcd(a, m) != 1:
return None # no mod inverse if a & m aren't relatively prime
# Calculate using the Extended Euclidean Algorithm:
u1, u2, u3 = 1, 0, a
v1, v2, v3 = 0, 1, m
while v3 != 0:
q = u3 // v3 # // is the integer division operator
v1, v2, v3, u1, u2, u3 = (u1 - q * v1), (u2 - q * v2), (u3 - q * v3), v1, v2, v3
return u1 % m
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After you've created the cryptomath, proceed to the cipher.
The source code for the same is below.
SOURCE CODE :-
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import sys, pyperclip, cryptomath, random
SYMBOLS = """ !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJKLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~""" # note the space at the front
def main():
myMessage = str(input("ENTER YOUR MESSAGE NOW"))
myKey = int(input("ENTER YOUR KEY"))
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()
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source- www.inventwithpython.com
