#2: Implementing Vigenere-Chiffre

chapter_two/Vigenere-Chiffre.py

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+from utils import AlphabetUtils as au
+
+
+def encrypt_text(cleartext: str, keyword: str) -> str:
+	"""
+	Encrypts the given text with the given keyword
+	:param cleartext: The text to encrypt
+	:param keyword: The keyword to use
+	:return: The encrypted text
+	"""
+
+	# If the ciphertext is longer than the keyword, we need to multiply the keyword
+	while len(cleartext) > len(keyword):
+		keyword += keyword
+
+	resulting = ''
+
+	for char_index in range(len(cleartext)):
+		char = cleartext[char_index]
+		key = keyword[char_index]
+		cipherchar = _get_corresponding_cipher(char, key)
+		resulting += cipherchar
+
+	return resulting
+
+
+def decrypt_text(ciphertext: str, keyword: str) -> str:
+	"""
+	Decrypts the given ciphertext with the given keyword
+	:param ciphertext: The text to decrypt
+	:param keyword: The keyword to use
+	:return: The decrypted text
+	"""
+
+	# If the ciphertext is longer than the keyword, we need to multiply the keyword
+	while len(ciphertext) > len(keyword):
+		keyword += keyword
+
+	resulting = ''
+
+	for char_index in range(len(ciphertext)):
+		char = ciphertext[char_index]
+		key = keyword[char_index]
+		clearchar = _get_corresponding_char(char, key)
+		resulting += clearchar
+
+	return resulting
+
+
+def _get_corresponding_cipher(char: str, key: str) -> str:
+	"""
+	Calculates the corresponding cipher char for the given clearchar/keychar combination using the vigenere square
+	:param char: The cleartext char
+	:param key: The keyword char
+	:return: The cipher char
+	"""
+	char_index = au.get_index_of_letter(char)
+	key_index = au.get_index_of_letter(key)
+
+	# Based on the layout of the vigenere square, this should in theory work
+	cipher_index = (char_index + key_index) % 26
+
+	return au.get_letter_at_index(cipher_index)
+
+
+def _get_corresponding_char(cipher: str, key: str) -> str:
+	"""
+	Calculates the corresponding cleartext char for the given cipherchar/keychar combination using the vigenere square
+	:param cipher: The cipher char
+	:param key: The keyword char
+	:return: The cleartext char
+	"""
+	cipher_index = au.get_index_of_letter(cipher)
+	key_index = au.get_index_of_letter(key)
+
+	# Based on the layout of the vigenere square, this should in theory work
+	char_index = (cipher_index - key_index) % 26
+
+	return au.get_letter_at_index(char_index)
+
+
+if __name__ == '__main__':
+	print(encrypt_text('BonkRocks', 'SuperSecretKeyword'))
+	print(decrypt_text('ticoiggmj', 'SuperSecretKeyword'))