Decrypt Ruby's ActiveSupport::MessageEncryptor on Python 3

decrypt_ruby_MessageEncryptor.py

import hashlib
import base64
from Crypto import Random
from Crypto.Cipher import AES
import rubymarshal.reader
from pbkdf2 import PBKDF2

SECRET = "a3f58debfe0c5b71edaebea3a627f4f"
SALT = "12345"
ITERATIONS = 65536
KEY_LENGTH = 32
ruby_encrypted_message = "" # "salt.base64message--base64salt--base64signature"
                            # we dont check for signature

parts = ruby_encrypted_message.split(".")[1].split("--")

key = PBKDF2(SECRET, SALT, ITERATIONS).read(KEY_LENGTH)
ciphertext = parts[0]
iv = parts[1]
aes = AES.new(key, AES.MODE_GCM, iv)
aes.decrypt(ciphertext)
data = rubymarshal.reader.loads(decrypted)

print(data) # plaintext