Authenticate trezor to user

auth.py

"""
You can use the `authenticate_trezor` function to be sure
that your connected trezor has the private key to the provided
public key.
For example:
your trezor is password protected:
before sending your secret password to the trezor,
you can authenticate the trezor to you.
"""
import base64
import datetime
import ecdsa
import hashlib
import random
import sys
from trezorlib.client import TrezorClient
from trezorlib.transport import get_transport
from trezorlib import tools, ui, btc

MESSAGE = '{date}: {r1},{r2}'


def trezor_sign_message(client, message, coin='Bitcoin', address='0'):
    address_n = tools.parse_path(address)
    res = btc.sign_message(client, coin, address_n, message, None)
    return {
        "message": message,
        "address": res.address,
        "signature": base64.b64encode(res.signature).decode(),
    }


def get_trezor(trezor_path=None):
    try:
        device = get_transport(trezor_path, prefix_search=False)
    except Exception:
        try:
            device = get_transport(trezor_path, prefix_search=True)
        except Exception:
            print("Failed to find a Trezor device.")
            if trezor_path is not None:
                print("Using path: {}".format(trezor_path))
            sys.exit(1)
    client = TrezorClient(transport=device, ui=ui.ClickUI())
    return client


def random_number():
    return int(random.random() * 100000)


class DoubleSha256:

    def __init__(self, *args, **kwargs):
        self._m = hashlib.sha256(*args, **kwargs)

    def __getattr__(self, attr):
        if attr == 'digest':
            return self.double_digest
        return getattr(self._m, attr)

    def double_digest(self):
        m = hashlib.sha256()
        m.update(self._m.digest())
        return m.digest()


def pad_bitcoin_sign_message(message):
    return ("\x18Bitcoin Signed Message:\n".encode('UTF-8') +
            bytes([len(message)]) + message.encode('UTF-8'))


def verify_message(signature_b64, public_key_hex, message):
    public_key = bytes.fromhex(public_key_hex)
    padded_message = pad_bitcoin_sign_message(message)
    sig = base64.b64decode(signature_b64)
    vk = ecdsa.VerifyingKey.from_string(public_key, curve=ecdsa.SECP256k1)
    return vk.verify(sig[1:], padded_message, hashfunc=DoubleSha256)


def authenticate_trezor(public_key_hex, coin='Bitcoin', trezor_path=None):
    trezor = get_trezor(trezor_path)
    message = MESSAGE.format(date=str(datetime.datetime.now()),
                             r1=random_number(),
                             r2=random_number())
    print("Message: '{}'".format(message))
    signed_result = trezor_sign_message(client=trezor,
                                        message=message,
                                        coin=coin)
    success = verify_message(signature_b64=signed_result['signature'],
                             public_key_hex=public_key_hex,
                             message=message)
    print("verified message: {}".format(success))
    return signed_result