import base64

from cryptography.fernet import Fernet, InvalidToken

def encrypt_string(string, key):
  """ Encrypts a string with the specified key. The key must be 32 raw bytes. """
  f = Fernet(base64.urlsafe_b64encode(key))
  return f.encrypt(string)

def decrypt_string(string, key, ttl=None):
  """ Decrypts an encrypted string with the specified key. The key must be 32 raw bytes. """
  f = Fernet(base64.urlsafe_b64encode(key))
  try:
    return f.decrypt(string, ttl=ttl)
  except InvalidToken:
    return None
  except TypeError:
    return None