Sign EIP712 message from python code

Question

My goal is to sign a message according to EIP712 from python code using an imported private key.

To construct the message to sign I am using: https://github.com/ConsenSys/py-eip712-structs

After creating the right object I can convert it either into:

# Into a message dict - domain required
my_msg = mine.to_message(domain)

# Into message JSON - domain required.
# This method converts bytes types for you, which the default JSON encoder won't handle.
my_msg_json = mine.to_message_json(domain)

# Into signable bytes - domain required
my_bytes = mine.signable_bytes(domain)

However - it is not clear to me how to proceed from here. Which of those 3 outputs can I use as input for: https://web3py.readthedocs.io/en/stable/web3.eth.account.html?highlight=sign#sign-a-message

Or do I need to use: https://web3py.readthedocs.io/en/stable/web3.eth.html?highlight=structured#web3.eth.Eth.sign_typed_data

Unfortunately this apparently just forwards to an PRC-node so it is not possible to use this from just within python.

Answer 1

"Signable bytes" may need to be passed into keccak256() if the EIP712 library didn't already do that for you. Sign the keccak256 hash to make a signature.