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