Python script that signs EIP712 structs that can be validated by EVM smart contracts

eip712-sign.py

# Python script that signs EIP712 structs that can be validated
# by EVM smart contracts.
#
# Copyright (c) 2021 Alexis Robert <[email protected]>
#
# Dependencies:
#   coincurve==15.0.1
#   eip712-structs==1.1.0

import os
import sha3

from eip712_structs import EIP712Struct, Address, String, Uint
from eip712_structs import make_domain
from eth_utils import big_endian_to_int
from coincurve import PrivateKey, PublicKey

keccak_hash = lambda x : sha3.keccak_256(x).digest()

# Configuration of the EIP712 domain
my_domain = make_domain(name='TestContract',
                        version='0.1',
                        chainId=80001,
                        verifyingContract='0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF')

# Configuration of the EIP712 message struct
class Mail(EIP712Struct):
  to = Address()
  contents = String()

# Instanciation of a new EIP712 message
msg = Mail()
msg['to'] = '0xFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFFF'
msg['contents'] = "Hello world!"

# Converting it to signable bytes
signable_bytes = msg.signable_bytes(my_domain)

# Now ... sign it :)
pk = PrivateKey.from_hex(os.getenv('PRIVATE_KEY'))
signature = pk.sign_recoverable(signable_bytes, hasher=keccak_hash)
v = signature[64] + 27
r = big_endian_to_int(signature[0:32])
s = big_endian_to_int(signature[32:64])

final_sig = r.to_bytes(32, 'big') + s.to_bytes(32, 'big') + v.to_bytes(1, 'big')

print("Signature:",final_sig.hex())