$ pip install otpad
from cryptography.fernet import Fernet
import otpad
k1 = Fernet.generate_key()
k2 = Fernet.generate_key()
k3 = Fernet.generate_key()
padded = otpad.pad(k1, k2, hmac_key=k3)
orig = unpad(k1, padded['encrypted'], hmac_key=k3, hmac_digest=padded['digest'])