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#!/usr/bin/env python3
"""
The Bifid Cipher uses a Polybius Square to encipher a message in a way that
makes it fairly difficult to decipher without knowing the secret.
https://www.braingle.com/brainteasers/codes/bifid.php
"""
importnumpyasnp
SQUARE= [
["a", "b", "c", "d", "e"],
["f", "g", "h", "i", "k"],
["l", "m", "n", "o", "p"],
["q", "r", "s", "t", "u"],
["v", "w", "x", "y", "z"],
]
classBifidCipher:
def__init__(self) ->None:
self.SQUARE=np.array(SQUARE)
defletter_to_numbers(self, letter: str) ->np.ndarray:
"""
Return the pair of numbers that represents the given letter in the
polybius square
>>> np.array_equal(BifidCipher().letter_to_numbers('a'), [1,1])
True
>>> np.array_equal(BifidCipher().letter_to_numbers('u'), [4,5])
True
"""
index1, index2=np.where(letter==self.SQUARE)
indexes=np.concatenate([index1+1, index2+1])
returnindexes
defnumbers_to_letter(self, index1: int, index2: int) ->str:
"""
Return the letter corresponding to the position [index1, index2] in
the polybius square
>>> BifidCipher().numbers_to_letter(4, 5) == "u"
True
>>> BifidCipher().numbers_to_letter(1, 1) == "a"
True
"""
letter=self.SQUARE[index1-1, index2-1]
returnletter
defencode(self, message: str) ->str:
"""
Return the encoded version of message according to the polybius cipher
>>> BifidCipher().encode('testmessage') == 'qtltbdxrxlk'
True
>>> BifidCipher().encode('Test Message') == 'qtltbdxrxlk'
True
>>> BifidCipher().encode('test j') == BifidCipher().encode('test i')
True
"""
message=message.lower()
message=message.replace(" ", "")
message=message.replace("j", "i")
first_step=np.empty((2, len(message)))
forletter_indexinrange(len(message)):
numbers=self.letter_to_numbers(message[letter_index])
first_step[0, letter_index] =numbers[0]
first_step[1, letter_index] =numbers[1]
second_step=first_step.reshape(2*len(message))
encoded_message=""
fornumbers_indexinrange(len(message)):
index1=int(second_step[numbers_index*2])
index2=int(second_step[(numbers_index*2) +1])
letter=self.numbers_to_letter(index1, index2)
encoded_message=encoded_message+letter
returnencoded_message
defdecode(self, message: str) ->str:
"""
Return the decoded version of message according to the polybius cipher
>>> BifidCipher().decode('qtltbdxrxlk') == 'testmessage'
True
"""
message=message.lower()
message.replace(" ", "")
first_step=np.empty(2*len(message))
forletter_indexinrange(len(message)):
numbers=self.letter_to_numbers(message[letter_index])
first_step[letter_index*2] =numbers[0]
first_step[letter_index*2+1] =numbers[1]
second_step=first_step.reshape((2, len(message)))
decoded_message=""
fornumbers_indexinrange(len(message)):
index1=int(second_step[0, numbers_index])
index2=int(second_step[1, numbers_index])
letter=self.numbers_to_letter(index1, index2)
decoded_message=decoded_message+letter
returndecoded_message