trezor-firmware/core/src/apps/bitcoin/sign_tx/tx_info.py

from micropython import const

from trezor import wire
from trezor.crypto.hashlib import sha256
from trezor.utils import HashWriter

from .. import common, writers
from ..common import BIP32_WALLET_DEPTH, input_is_external
from .matchcheck import MultisigFingerprintChecker, WalletPathChecker

if False:
    from typing import Optional, Protocol, Union
    from trezor.messages.SignTx import SignTx
    from trezor.messages.PrevTx import PrevTx
    from trezor.messages.TxInput import TxInput
    from trezor.messages.TxOutput import TxOutput
    from trezor.messages.PrevInput import PrevInput
    from trezor.messages.PrevOutput import PrevOutput
    from .hash143 import Hash143

    from apps.common.coininfo import CoinInfo

    class Signer(Protocol):
        coin = ...  # type: CoinInfo

        def create_hash_writer(self) -> HashWriter:
            ...

        def create_hash143(self) -> Hash143:
            ...

        def write_tx_header(
            self,
            w: writers.Writer,
            tx: Union[SignTx, PrevTx],
            witness_marker: bool,
        ) -> None:
            ...

        @staticmethod
        def write_tx_input(
            w: writers.Writer,
            txi: Union[TxInput, PrevInput],
            script: bytes,
        ) -> None:
            ...

        @staticmethod
        def write_tx_output(
            w: writers.Writer,
            txo: Union[TxOutput, PrevOutput],
            script_pubkey: bytes,
        ) -> None:
            ...

        async def write_prev_tx_footer(
            self, w: writers.Writer, tx: PrevTx, prev_hash: bytes
        ) -> None:
            ...


# The chain id used for change.
_BIP32_CHANGE_CHAIN = const(1)

# The maximum allowed change address. This should be large enough for normal
# use and still allow to quickly brute-force the correct BIP32 path.
_BIP32_MAX_LAST_ELEMENT = const(1000000)

# Setting nSequence to this value for every input in a transaction disables nLockTime.
_SEQUENCE_FINAL = const(0xFFFFFFFF)


class TxInfoBase:
    def __init__(self, signer: Signer) -> None:
        # Checksum of multisig inputs, used to validate change-output.
        self.multisig_fingerprint = MultisigFingerprintChecker()

        # Common prefix of input paths, used to validate change-output.
        self.wallet_path = WalletPathChecker()

        # h_tx_check is used to make sure that the inputs and outputs streamed in
        # different steps are the same every time, e.g. the ones streamed for approval
        # in Steps 1 and 2 and the ones streamed for signing legacy inputs in Step 4.
        self.h_tx_check = HashWriter(sha256())  # not a real tx hash

        # BIP-0143 transaction hashing.
        self.hash143 = signer.create_hash143()

        # The minimum nSequence of all inputs.
        self.min_sequence = _SEQUENCE_FINAL

    def add_input(self, txi: TxInput) -> None:
        self.hash143.add_input(txi)  # all inputs are included (non-segwit as well)
        writers.write_tx_input_check(self.h_tx_check, txi)
        self.min_sequence = min(self.min_sequence, txi.sequence)

        if not input_is_external(txi):
            self.wallet_path.add_input(txi)
            self.multisig_fingerprint.add_input(txi)

    def add_output(self, txo: TxOutput, script_pubkey: bytes) -> None:
        self.hash143.add_output(txo, script_pubkey)
        writers.write_tx_output(self.h_tx_check, txo, script_pubkey)

    def check_input(self, txi: TxInput) -> None:
        self.wallet_path.check_input(txi)
        self.multisig_fingerprint.check_input(txi)

    def output_is_change(self, txo: TxOutput) -> bool:
        if txo.script_type not in common.CHANGE_OUTPUT_SCRIPT_TYPES:
            return False
        if txo.multisig and not self.multisig_fingerprint.output_matches(txo):
            return False
        return (
            self.wallet_path.output_matches(txo)
            and len(txo.address_n) >= BIP32_WALLET_DEPTH
            and txo.address_n[-2] <= _BIP32_CHANGE_CHAIN
            and txo.address_n[-1] <= _BIP32_MAX_LAST_ELEMENT
            and txo.amount > 0
        )

    def lock_time_disabled(self) -> bool:
        return self.min_sequence == _SEQUENCE_FINAL


# Used to keep track of the transaction currently being signed.
class TxInfo(TxInfoBase):
    def __init__(self, signer: Signer, tx: SignTx) -> None:
        super().__init__(signer)
        self.tx = tx

        # h_inputs is a digest of the inputs streamed for approval in Step 1, which
        # is used to ensure that the inputs streamed for verification in Step 3 are
        # the same as those in Step 1.
        self.h_inputs = None  # type: Optional[bytes]