Create keyword_cipher.py

Cryptography/src/Keyword Cipher/keyword_cipher.py

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+''' 
+  Python Implementation Of Keyword Cipher
+  Author : Mohit Kumar
+
+  A keyword cipher is a form of monoalphabetic substitution. A keyword is used as the key, and it determines the letter matchings of the cipher alphabet
+  to the plain alphabet.Repeats of letters in the word are removed, then the cipher alphabet is generated with the keyword matching to A, B, C etc
+
+'''
+
+def remove_duplicates(key: str) -> str:
+    """
+    Removes duplicate alphabetic characters in a keyword (letter is ignored after its
+        first appearance).
+    :param key: Keyword to use
+    :return: String with duplicates removed
+    >>> remove_duplicates('Hello World!!')
+    'Helo Wrd'
+    """
+
+    key_no_dups = ""
+    for ch in key:
+        if ch == " " or ch not in key_no_dups and ch.isalpha():
+            key_no_dups += ch
+    return key_no_dups
+
+
+def create_cipher_map(key: str) -> dict:
+    """
+    Returns a cipher map given a keyword.
+    :param key: keyword to use
+    :return: dictionary cipher map
+    """
+    # Create alphabet list
+    alphabet = [chr(i + 65) for i in range(26)]
+    # Remove duplicate characters from key
+    key = remove_duplicates(key.upper())
+    offset = len(key)
+    # First fill cipher with key characters
+    cipher_alphabet = {alphabet[i]: char for i, char in enumerate(key)}
+    # Then map remaining characters in alphabet to
+    # the alphabet from the beginning
+    for i in range(len(cipher_alphabet), 26):
+        char = alphabet[i - offset]
+        # Ensure we are not mapping letters to letters previously mapped
+        while char in key:
+            offset -= 1
+            char = alphabet[i - offset]
+        cipher_alphabet[alphabet[i]] = char
+    return cipher_alphabet
+
+
+def encipher(message: str, cipher_map: dict) -> str:
+    """
+    Enciphers a message given a cipher map.
+    :param message: Message to encipher
+    :param cipher_map: Cipher map
+    :return: enciphered string
+    >>> encipher('Hello World!!', create_cipher_map('Goodbye!!'))
+    'CYJJM VMQJB!!'
+    """
+    return "".join(cipher_map.get(ch, ch) for ch in message.upper())
+
+
+def decipher(message: str, cipher_map: dict) -> str:
+    """
+    Deciphers a message given a cipher map
+    :param message: Message to decipher
+    :param cipher_map: Dictionary mapping to use
+    :return: Deciphered string
+    >>> cipher_map = create_cipher_map('Goodbye!!')
+    >>> decipher(encipher('Hello World!!', cipher_map), cipher_map)
+    'HELLO WORLD!!'
+    """
+    # Reverse our cipher mappings
+    rev_cipher_map = {v: k for k, v in cipher_map.items()}
+    return "".join(rev_cipher_map.get(ch, ch) for ch in message.upper())
+
+
+def main():
+    """
+    Handles I/O
+    :return: void
+    """
+    message = input("Enter message to encode or decode: ").strip()
+    key = input("Enter keyword: ").strip()
+    option = input("Encipher or decipher? E/D:").strip()[0].lower()
+    try:
+        func = {"e": encipher, "d": decipher}[option]
+    except KeyError:
+        raise KeyError("invalid input option")
+    cipher_map = create_cipher_map(key)
+    print(func(message, cipher_map))
+
+
+if __name__ == "__main__":
+    import doctest
+
+    doctest.testmod()
+    main()