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# Transposition Cipher Decryption
# http://inventwithpython.com/hacking (BSD Licensed)
import math, pyperclip
def main():
myMessage = 'Cenoonommstmme oo snnio. s s c'
myKey = 8
plaintext = decryptMessage(myKey, myMessage)
# Print with a | (called "pipe" character) after it in case
# there are spaces at the end of the decrypted message.
print(plaintext + '|')
pyperclip.copy(plaintext)
def decryptMessage(key, message):
# The transposition decrypt function will simulate the "columns" and
# "rows" of the grid that the plaintext is written on by using a list
# of strings. First, we need to calculate a few values.
# The number of "columns" in our transposition grid:
numOfColumns = math.ceil(len(message) / key)
# The number of "rows" in our grid will need:
numOfRows = key
# The number of "shaded boxes" in the last "column" of the grid:
numOfShadedBoxes = (numOfColumns * numOfRows) - len(message)
# Each string in plaintext represents a column in the grid.
plaintext = [''] * numOfColumns
# The col and row variables point to where in the grid the next
# character in the encrypted message will go.
col = 0
row = 0
for symbol in message:
plaintext[col] += symbol
col += 1 # point to next column
# If there are no more columns OR we're at a shaded box, go back to
# the first column and the next row.
if (col == numOfColumns) or (col == numOfColumns - 1 and row >= numOfRows - numOfShadedBoxes):
col = 0
row += 1
return ''.join(plaintext)
# If transpositionDecrypt.py is run (instead of imported as a module) call
# the main() function.
if __name__ == '__main__':
main()
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