## Python, , transposition_cipher.py

``````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() -> None:
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: int, message: str) -> str:
"""
>>> 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: int, message: str) -> str:
"""
>>> 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()
``````