Python/ciphers/transposition_cipher.py

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import math
"""
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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.
"""
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def main():
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message = input("Enter message: ")
key = int(input("Enter key [2-%s]: " % (len(message) - 1)))
mode = input("Encryption/Decryption [e/d]: ")
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if mode.lower().startswith("e"):
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text = encryptMessage(key, message)
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elif mode.lower().startswith("d"):
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text = decryptMessage(key, message)
# Append pipe symbol (vertical bar) to identify spaces at the end.
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print("Output:\n%s" % (text + "|"))
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def encryptMessage(key, message):
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"""
>>> encryptMessage(6, 'Harshil Darji')
'Hlia rDsahrij'
"""
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cipherText = [""] * key
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for col in range(key):
pointer = col
while pointer < len(message):
cipherText[col] += message[pointer]
pointer += key
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return "".join(cipherText)
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def decryptMessage(key, message):
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"""
>>> decryptMessage(6, 'Hlia rDsahrij')
'Harshil Darji'
"""
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numCols = math.ceil(len(message) / key)
numRows = key
numShadedBoxes = (numCols * numRows) - len(message)
plainText = [""] * numCols
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col = 0
row = 0
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for symbol in message:
plainText[col] += symbol
col += 1
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if (
(col == numCols)
or (col == numCols - 1)
and (row >= numRows - numShadedBoxes)
):
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col = 0
row += 1
return "".join(plainText)
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if __name__ == "__main__":
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import doctest
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doctest.testmod()
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main()