#### Trafid Cipher

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```# https://en.wikipedia.org/wiki/Trifid_cipher
from __future__ import annotations

def __encrypt_part(message_part: str, character_to_number: dict[str, str]) -> str:
one, two, three = "", "", ""
tmp = []

for character in message_part:
tmp.append(character_to_number[character])

for each in tmp:
one += each[0]
two += each[1]
three += each[2]

return one + two + three

def __decrypt_part(
message_part: str, character_to_number: dict[str, str]
) -> tuple[str, str, str]:
tmp, this_part = "", ""
result = []

for character in message_part:
this_part += character_to_number[character]

for digit in this_part:
tmp += digit
if len(tmp) == len(message_part):
result.append(tmp)
tmp = ""

return result[0], result[1], result[2]

def __prepare(
message: str, alphabet: str
) -> tuple[str, str, dict[str, str], dict[str, str]]:
# Validate message and alphabet, set to upper and remove spaces
alphabet = alphabet.replace(" ", "").upper()
message = message.replace(" ", "").upper()

# Check length and characters
if len(alphabet) != 27:
raise KeyError("Length of alphabet has to be 27.")
for each in message:
if each not in alphabet:
raise ValueError("Each message character has to be included in alphabet!")

# Generate dictionares
numbers = (
"111",
"112",
"113",
"121",
"122",
"123",
"131",
"132",
"133",
"211",
"212",
"213",
"221",
"222",
"223",
"231",
"232",
"233",
"311",
"312",
"313",
"321",
"322",
"323",
"331",
"332",
"333",
)
character_to_number = {}
number_to_character = {}
for letter, number in zip(alphabet, numbers):
character_to_number[letter] = number
number_to_character[number] = letter

return message, alphabet, character_to_number, number_to_character

def encrypt_message(
message: str, alphabet: str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ.", period: int = 5
) -> str:
message, alphabet, character_to_number, number_to_character = __prepare(
message, alphabet
)
encrypted, encrypted_numeric = "", ""

for i in range(0, len(message) + 1, period):
encrypted_numeric += __encrypt_part(
message[i : i + period], character_to_number
)

for i in range(0, len(encrypted_numeric), 3):
encrypted += number_to_character[encrypted_numeric[i : i + 3]]

return encrypted

def decrypt_message(
message: str, alphabet: str = "ABCDEFGHIJKLMNOPQRSTUVWXYZ.", period: int = 5
) -> str:
message, alphabet, character_to_number, number_to_character = __prepare(
message, alphabet
)
decrypted_numeric = []
decrypted = ""

for i in range(0, len(message) + 1, period):
a, b, c = __decrypt_part(message[i : i + period], character_to_number)

for j in range(len(a)):
decrypted_numeric.append(a[j] + b[j] + c[j])

for each in decrypted_numeric:
decrypted += number_to_character[each]

return decrypted

if __name__ == "__main__":
msg = "DEFEND THE EAST WALL OF THE CASTLE."
encrypted = encrypt_message(msg, "EPSDUCVWYM.ZLKXNBTFGORIJHAQ")
decrypted = decrypt_message(encrypted, "EPSDUCVWYM.ZLKXNBTFGORIJHAQ")
print(f"Encrypted: {encrypted}\nDecrypted: {decrypted}")
```