In cryptanalysis, a transposition cipher is a method of encryption by which the positions hold by units of plaintext (which are normally characters or groups of characters) are shifted according to a regular system, so that the ciphertext constitutes a permutation of the plaintext. mathematically a bijective function is used on the characters' positions to cipher and an inverse function to decrypt.
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()