Added fractionated_morse_cipher (#9442)

* Added fractionated_morse_cipher

* Added return type hint for main function

* Added doctest for main

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* Replaced main function

* changed the references section

Co-authored-by: Christian Clauss <cclauss@me.com>

* removed repetitive datatype hint in the docstring

Co-authored-by: Christian Clauss <cclauss@me.com>

* changed dictionary comprehension variable names to something more compact

Co-authored-by: Christian Clauss <cclauss@me.com>

* Update fractionated_morse_cipher.py

---------

Co-authored-by: pre-commit-ci[bot] <66853113+pre-commit-ci[bot]@users.noreply.github.com>
Co-authored-by: Christian Clauss <cclauss@me.com>

ciphers/fractionated_morse_cipher.py

@@ -0,0 +1,167 @@
+"""
+Python program for the Fractionated Morse Cipher.
+
+The Fractionated Morse cipher first converts the plaintext to Morse code,
+then enciphers fixed-size blocks of Morse code back to letters.
+This procedure means plaintext letters are mixed into the ciphertext letters,
+making it more secure than substitution ciphers.
+
+http://practicalcryptography.com/ciphers/fractionated-morse-cipher/
+"""
+import string
+
+MORSE_CODE_DICT = {
+    "A": ".-",
+    "B": "-...",
+    "C": "-.-.",
+    "D": "-..",
+    "E": ".",
+    "F": "..-.",
+    "G": "--.",
+    "H": "....",
+    "I": "..",
+    "J": ".---",
+    "K": "-.-",
+    "L": ".-..",
+    "M": "--",
+    "N": "-.",
+    "O": "---",
+    "P": ".--.",
+    "Q": "--.-",
+    "R": ".-.",
+    "S": "...",
+    "T": "-",
+    "U": "..-",
+    "V": "...-",
+    "W": ".--",
+    "X": "-..-",
+    "Y": "-.--",
+    "Z": "--..",
+    " ": "",
+}
+
+# Define possible trigrams of Morse code
+MORSE_COMBINATIONS = [
+    "...",
+    "..-",
+    "..x",
+    ".-.",
+    ".--",
+    ".-x",
+    ".x.",
+    ".x-",
+    ".xx",
+    "-..",
+    "-.-",
+    "-.x",
+    "--.",
+    "---",
+    "--x",
+    "-x.",
+    "-x-",
+    "-xx",
+    "x..",
+    "x.-",
+    "x.x",
+    "x-.",
+    "x--",
+    "x-x",
+    "xx.",
+    "xx-",
+    "xxx",
+]
+
+# Create a reverse dictionary for Morse code
+REVERSE_DICT = {value: key for key, value in MORSE_CODE_DICT.items()}
+
+
+def encode_to_morse(plaintext: str) -> str:
+    """Encode a plaintext message into Morse code.
+
+    Args:
+        plaintext: The plaintext message to encode.
+
+    Returns:
+        The Morse code representation of the plaintext message.
+
+    Example:
+        >>> encode_to_morse("defend the east")
+        '-..x.x..-.x.x-.x-..xx-x....x.xx.x.-x...x-'
+    """
+    return "x".join([MORSE_CODE_DICT.get(letter.upper(), "") for letter in plaintext])
+
+
+def encrypt_fractionated_morse(plaintext: str, key: str) -> str:
+    """Encrypt a plaintext message using Fractionated Morse Cipher.
+
+    Args:
+        plaintext: The plaintext message to encrypt.
+        key: The encryption key.
+
+    Returns:
+        The encrypted ciphertext.
+
+    Example:
+        >>> encrypt_fractionated_morse("defend the east","Roundtable")
+        'ESOAVVLJRSSTRX'
+
+    """
+    morse_code = encode_to_morse(plaintext)
+    key = key.upper() + string.ascii_uppercase
+    key = "".join(sorted(set(key), key=key.find))
+
+    # Ensure morse_code length is a multiple of 3
+    padding_length = 3 - (len(morse_code) % 3)
+    morse_code += "x" * padding_length
+
+    fractionated_morse_dict = {v: k for k, v in zip(key, MORSE_COMBINATIONS)}
+    fractionated_morse_dict["xxx"] = ""
+    encrypted_text = "".join(
+        [
+            fractionated_morse_dict[morse_code[i : i + 3]]
+            for i in range(0, len(morse_code), 3)
+        ]
+    )
+    return encrypted_text
+
+
+def decrypt_fractionated_morse(ciphertext: str, key: str) -> str:
+    """Decrypt a ciphertext message encrypted with Fractionated Morse Cipher.
+
+    Args:
+        ciphertext: The ciphertext message to decrypt.
+        key: The decryption key.
+
+    Returns:
+        The decrypted plaintext message.
+
+    Example:
+        >>> decrypt_fractionated_morse("ESOAVVLJRSSTRX","Roundtable")
+        'DEFEND THE EAST'
+    """
+    key = key.upper() + string.ascii_uppercase
+    key = "".join(sorted(set(key), key=key.find))
+
+    inverse_fractionated_morse_dict = dict(zip(key, MORSE_COMBINATIONS))
+    morse_code = "".join(
+        [inverse_fractionated_morse_dict.get(letter, "") for letter in ciphertext]
+    )
+    decrypted_text = "".join(
+        [REVERSE_DICT[code] for code in morse_code.split("x")]
+    ).strip()
+    return decrypted_text
+
+
+if __name__ == "__main__":
+    """
+    Example usage of Fractionated Morse Cipher.
+    """
+    plaintext = "defend the east"
+    print("Plain Text:", plaintext)
+    key = "ROUNDTABLE"
+
+    ciphertext = encrypt_fractionated_morse(plaintext, key)
+    print("Encrypted:", ciphertext)
+
+    decrypted_text = decrypt_fractionated_morse(ciphertext, key)
+    print("Decrypted:", decrypted_text)