[6]-Columnar Transposition.py

import math 
  
key = "HACK"

def encryptMessage(msg): 
    cipher = "" 
    k_indx = 0
    msg_len = float(len(msg)) 
    msg_lst = list(msg) 
    key_lst = sorted(list(key)) 
  
    # calculate column of the matrix 
    col = len(key) 
      
    # calculate maximum row of the matrix 
    row = int(math.ceil(msg_len / col)) 
  
    # add the padding character '_' in empty 
    fill_null = int((row * col) - msg_len) 
    msg_lst.extend('_' * fill_null) 
  
    # create Matrix and insert message  
    matrix = [msg_lst[i: i + col]  
              for i in range(0, len(msg_lst), col)] 
  
    # read matrix column-wise using key 
    for _ in range(col): 
        curr_idx = key.index(key_lst[k_indx]) 
        cipher += ''.join([row[curr_idx]  for row in matrix]) 
        k_indx += 1
    return cipher 
 
def decryptMessage(cipher): 
    msg = "" 
    k_indx = 0

    msg_indx = 0
    msg_len = float(len(cipher)) 
    msg_lst = list(cipher) 
  
    # calculate column of the matrix 
    col = len(key) 
      
    # calculate maximum row of the matrix 
    row = int(math.ceil(msg_len / col)) 
  
    # convert key into list and sort  
    # alphabetically so we can access  
    # each character by its alphabetical position. 
    key_lst = sorted(list(key)) 
  
    # create an empty matrix to  
    # store deciphered message 
    dec_cipher = [] 
    for _ in range(row): 
        dec_cipher += [[None] * col] 
  
    # Arrange the matrix column wise according  
    # to permutation order by adding into new matrix 
    for _ in range(col): 
        curr_idx = key.index(key_lst[k_indx]) 
  
        for j in range(row): 
            dec_cipher[j][curr_idx] = msg_lst[msg_indx] 
            msg_indx += 1
        k_indx += 1
  
    # convert decrypted msg matrix into a string 
    try: 
        msg = ''.join(sum(dec_cipher, [])) 
    except TypeError: 
        raise TypeError("This program cannot", 
                        "handle repeating words.") 
  
    null_count = msg.count('_') 
  
    if null_count > 0: 
        return msg[: -null_count] 
  
    return msg 

msg = "HelloWorld Nice"
cipher = encryptMessage(msg) 
print("Encrypted Message: {}". format(cipher))  
print("Decryped Message: {}". format(decryptMessage(cipher)))