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import math

"""

In cryptography, the TRANSPOSITION cipher is a method of encryption where the

positions of plaintext are shifted a certain number(determined by the key) that

follows a regular system that results in the permuted text, known as the encrypted

text. The type of transposition cipher demonstrated under is the ROUTE cipher.

"""

def main():

message = input("Enter message: ")

key = int(input("Enter key [2-%s]: " % (len(message) - 1)))

mode = input("Encryption/Decryption [e/d]: ")

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

text = encryptMessage(key, message)

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

text = decryptMessage(key, message)

# Append pipe symbol (vertical bar) to identify spaces at the end.

print("Output:\n%s" % (text + "|"))

def encryptMessage(key, message):

"""

>>> encryptMessage(6, 'Harshil Darji')

'Hlia rDsahrij'

"""

cipherText = [""] * key

for col in range(key):

pointer = col

while pointer < len(message):

cipherText[col] += message[pointer]

pointer += key

return "".join(cipherText)

def decryptMessage(key, message):

"""

>>> decryptMessage(6, 'Hlia rDsahrij')

'Harshil Darji'

"""

numCols = math.ceil(len(message) / key)

numRows = key

numShadedBoxes = (numCols * numRows) - len(message)

plainText = [""] * numCols

col = 0

row = 0

for symbol in message:

plainText[col] += symbol

col += 1

if (

(col == numCols)

or (col == numCols - 1)

and (row >= numRows - numShadedBoxes)

col = 0

row += 1

return "".join(plainText)

if __name__ == "__main__":

import doctest

doctest.testmod()

main()

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