trezor-firmware/core/src/apps/wallet/sign_tx/signing.py

import gc
from micropython import const

from trezor import utils
from trezor.crypto import base58, bip32, der
from trezor.crypto.curve import secp256k1
from trezor.crypto.hashlib import sha256
from trezor.messages import FailureType, InputScriptType, OutputScriptType
from trezor.messages.SignTx import SignTx
from trezor.messages.TransactionType import TransactionType
from trezor.messages.TxInputType import TxInputType
from trezor.messages.TxOutputBinType import TxOutputBinType
from trezor.messages.TxOutputType import TxOutputType
from trezor.messages.TxRequest import TxRequest
from trezor.messages.TxRequestDetailsType import TxRequestDetailsType
from trezor.messages.TxRequestSerializedType import TxRequestSerializedType

from apps.common import address_type, coininfo, seed
from apps.wallet.sign_tx import (
    addresses,
    helpers,
    multisig,
    progress,
    scripts,
    segwit_bip143,
    tx_weight,
    writers,
)

if False:
    from typing import Dict, List, Optional, Union

# the number of bip32 levels used in a wallet (chain and address)
_BIP32_WALLET_DEPTH = const(2)

# 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)


class SigningError(ValueError):
    pass


# Transaction signing
# ===
# see https://github.com/trezor/trezor-mcu/blob/master/firmware/signing.c#L84
# for pseudo code overview
# ===


class Bitcoin:
    async def signer(
        self, tx: SignTx, keychain: seed.Keychain, coin: coininfo.CoinInfo
    ) -> None:
        self.initialize(tx, keychain, coin)

        progress.init(self.tx.inputs_count, self.tx.outputs_count)

        # Add inputs to hash143 and h_confirmed and compute the sum of input amounts.
        await self.step1_process_inputs()

        # Add outputs to hash143 and h_confirmed, check previous transaction output
        # amounts, confirm outputs and compute sum of output amounts.
        await self.step2_confirm_outputs()

        # Check fee, confirm lock_time and total.
        await self.step3_confirm_tran()

        # Check that inputs are unchanged. Serialize inputs and sign the non-segwit ones.
        await self.step4_serialize_inputs()

        # Serialize outputs.
        await self.step5_serialize_outputs()

        # Sign segwit inputs and serialize witness data.
        await self.step6_sign_segwit_inputs()

        # Write footer and send remaining data.
        await self.step7_finish()

    def initialize(
        self, tx: SignTx, keychain: seed.Keychain, coin: coininfo.CoinInfo
    ) -> None:
        self.coin = coin
        self.tx = helpers.sanitize_sign_tx(tx, self.coin)
        self.keychain = keychain

        # checksum of multisig inputs, used to validate change-output
        self.multisig_fp = multisig.MultisigFingerprint()

        # common prefix of input paths, used to validate change-output
        self.wallet_path = []  # type: Optional[List[int]]

        # dict of booleans stating if input is segwit
        self.segwit = {}  # type: Dict[int, bool]

        self.total_in = 0  # sum of input amounts
        self.bip143_in = 0  # sum of segwit input amounts
        self.total_out = 0  # sum of output amounts
        self.change_out = 0  # change output amount
        self.weight = tx_weight.TxWeightCalculator(tx.inputs_count, tx.outputs_count)

        self.tx_req = TxRequest()
        self.tx_req.details = TxRequestDetailsType()
        self.tx_ser = TxRequestSerializedType()

        # h_confirmed is used to make sure that the inputs and outputs streamed for
        # confirmation in Steps 1 and 2 are the same as the ones streamed for signing
        # legacy inputs in Step 4.
        self.h_confirmed = self.create_hash_writer()  # not a real tx hash

        self.init_hash143()

    def init_hash143(self) -> None:
        self.hash143 = segwit_bip143.Bip143()  # BIP-0143 transaction hashing

    def create_hash_writer(self) -> utils.HashWriter:
        return utils.HashWriter(sha256())

    async def step1_process_inputs(self) -> None:
        for i in range(self.tx.inputs_count):
            # STAGE_REQUEST_1_INPUT
            progress.advance()
            txi = await helpers.request_tx_input(self.tx_req, i, self.coin)
            self.weight.add_input(txi)
            await self.process_input(i, txi)

    async def step2_confirm_outputs(self) -> None:
        txo_bin = TxOutputBinType()
        for i in range(self.tx.outputs_count):
            # STAGE_REQUEST_3_OUTPUT
            txo = await helpers.request_tx_output(self.tx_req, i, self.coin)
            txo_bin.amount = txo.amount
            txo_bin.script_pubkey = self.output_derive_script(txo)
            self.weight.add_output(txo_bin.script_pubkey)
            await self.confirm_output(i, txo, txo_bin)

    async def step3_confirm_tran(self) -> None:
        fee = self.total_in - self.total_out

        if fee < 0:
            self.on_negative_fee()

        # fee > (coin.maxfee per byte * tx size)
        if fee > (self.coin.maxfee_kb / 1000) * (self.weight.get_total() / 4):
            if not await helpers.confirm_feeoverthreshold(fee, self.coin):
                raise SigningError(FailureType.ActionCancelled, "Signing cancelled")

        if self.tx.lock_time > 0:
            if not await helpers.confirm_nondefault_locktime(self.tx.lock_time):
                raise SigningError(FailureType.ActionCancelled, "Locktime cancelled")

        if not await helpers.confirm_total(
            self.total_in - self.change_out, fee, self.coin
        ):
            raise SigningError(FailureType.ActionCancelled, "Total cancelled")

    async def step4_serialize_inputs(self) -> None:
        self.tx_req.serialized = None

        for i in range(self.tx.inputs_count):
            progress.advance()
            if self.segwit[i]:
                await self.serialize_segwit_input(i)
            else:
                await self.sign_nonsegwit_input(i)

    async def step5_serialize_outputs(self) -> None:
        for i in range(self.tx.outputs_count):
            progress.advance()
            await self.serialize_output(i)

    async def step6_sign_segwit_inputs(self) -> None:
        any_segwit = True in self.segwit.values()
        for i in range(self.tx.inputs_count):
            progress.advance()
            if self.segwit[i]:
                await self.sign_segwit_input(i)
            elif any_segwit:
                # TODO what if a non-segwit input follows after a segwit input?
                self.tx_ser.serialized_tx += bytearray(
                    1
                )  # empty witness for non-segwit inputs
                self.tx_ser.signature_index = None
                self.tx_ser.signature = None
                self.tx_req.serialized = self.tx_ser

    async def step7_finish(self) -> None:
        self.write_sign_tx_footer(self.tx_ser.serialized_tx)
        await helpers.request_tx_finish(self.tx_req)

    async def process_input(self, i: int, txi: TxInputType) -> None:
        self.input_extract_wallet_path(txi)
        writers.write_tx_input_check(self.h_confirmed, txi)
        self.hash143.add_prevouts(txi)  # all inputs are included (non-segwit as well)
        self.hash143.add_sequence(txi)

        if not addresses.validate_full_path(txi.address_n, self.coin, txi.script_type):
            await helpers.confirm_foreign_address(txi.address_n)

        if txi.multisig:
            self.multisig_fp.add(txi.multisig)
        else:
            self.multisig_fp.mismatch = True

        if txi.script_type in (
            InputScriptType.SPENDWITNESS,
            InputScriptType.SPENDP2SHWITNESS,
        ):
            await self.process_segwit_input(i, txi)
        elif txi.script_type in (
            InputScriptType.SPENDADDRESS,
            InputScriptType.SPENDMULTISIG,
        ):
            await self.process_nonsegwit_input(i, txi)
        else:
            raise SigningError(FailureType.DataError, "Wrong input script type")

    async def process_segwit_input(self, i: int, txi: TxInputType) -> None:
        if not txi.amount:
            raise SigningError(FailureType.DataError, "Segwit input without amount")
        self.segwit[i] = True
        self.bip143_in += txi.amount
        self.total_in += txi.amount

    async def process_nonsegwit_input(self, i: int, txi: TxInputType) -> None:
        self.segwit[i] = False
        self.total_in += await self.get_prevtx_output_value(
            txi.prev_hash, txi.prev_index
        )

    async def confirm_output(
        self, i: int, txo: TxOutputType, txo_bin: TxOutputBinType
    ) -> None:
        if self.change_out == 0 and self.output_is_change(txo):
            # output is change and does not need confirmation
            self.change_out = txo.amount
        elif not await helpers.confirm_output(txo, self.coin):
            raise SigningError(FailureType.ActionCancelled, "Output cancelled")

        writers.write_tx_output(self.h_confirmed, txo_bin)
        self.hash143.add_output(txo_bin)
        self.total_out += txo_bin.amount

    def on_negative_fee(self) -> None:
        raise SigningError(FailureType.NotEnoughFunds, "Not enough funds")

    async def serialize_segwit_input(self, i_sign: int) -> None:
        # STAGE_REQUEST_SEGWIT_INPUT
        txi_sign = await helpers.request_tx_input(self.tx_req, i_sign, self.coin)

        if not input_is_segwit(txi_sign):
            raise SigningError(
                FailureType.ProcessError, "Transaction has changed during signing"
            )
        self.input_check_wallet_path(txi_sign)
        # NOTE: No need to check the multisig fingerprint, because we won't be signing
        # the script here. Signatures are produced in STAGE_REQUEST_SEGWIT_WITNESS.

        key_sign = self.keychain.derive(txi_sign.address_n, self.coin.curve_name)
        key_sign_pub = key_sign.public_key()
        txi_sign.script_sig = self.input_derive_script(txi_sign, key_sign_pub)

        w_txi = writers.empty_bytearray(
            7 + len(txi_sign.prev_hash) + 4 + len(txi_sign.script_sig) + 4
        )
        if i_sign == 0:  # serializing first input => prepend headers
            self.write_sign_tx_header(w_txi, True)
        self.write_tx_input(w_txi, txi_sign)
        self.tx_ser.signature_index = None
        self.tx_ser.signature = None
        self.tx_ser.serialized_tx = w_txi
        self.tx_req.serialized = self.tx_ser

    async def sign_segwit_input(self, i: int) -> None:
        # STAGE_REQUEST_SEGWIT_WITNESS
        txi = await helpers.request_tx_input(self.tx_req, i, self.coin)

        self.input_check_wallet_path(txi)
        self.input_check_multisig_fingerprint(txi)

        if not input_is_segwit(txi) or txi.amount > self.bip143_in:
            raise SigningError(
                FailureType.ProcessError, "Transaction has changed during signing"
            )
        self.bip143_in -= txi.amount

        key_sign = self.keychain.derive(txi.address_n, self.coin.curve_name)
        key_sign_pub = key_sign.public_key()
        hash143_hash = self.hash143.preimage_hash(
            self.coin,
            self.tx,
            txi,
            addresses.ecdsa_hash_pubkey(key_sign_pub, self.coin),
            self.get_hash_type(),
        )

        signature = ecdsa_sign(key_sign, hash143_hash)
        if txi.multisig:
            # find out place of our signature based on the pubkey
            signature_index = multisig.multisig_pubkey_index(txi.multisig, key_sign_pub)
            witness = scripts.witness_p2wsh(
                txi.multisig, signature, signature_index, self.get_hash_type()
            )
        else:
            witness = scripts.witness_p2wpkh(
                signature, key_sign_pub, self.get_hash_type()
            )

        self.tx_ser.signature_index = i
        self.tx_ser.signature = signature
        self.tx_ser.serialized_tx = witness
        self.tx_req.serialized = self.tx_ser

    async def sign_nonsegwit_input(self, i_sign: int) -> None:
        # hash of what we are signing with this input
        h_sign = self.create_hash_writer()
        # should come out the same as h_confirmed, checked before signing the digest
        h_check = self.create_hash_writer()

        self.write_sign_tx_header(h_sign, has_segwit=False)

        for i in range(self.tx.inputs_count):
            # STAGE_REQUEST_4_INPUT
            txi = await helpers.request_tx_input(self.tx_req, i, self.coin)
            self.input_check_wallet_path(txi)
            writers.write_tx_input_check(h_check, txi)
            if i == i_sign:
                txi_sign = txi
                self.input_check_multisig_fingerprint(txi_sign)
                key_sign = self.keychain.derive(txi.address_n, self.coin.curve_name)
                key_sign_pub = key_sign.public_key()
                # for the signing process the script_sig is equal
                # to the previous tx's scriptPubKey (P2PKH) or a redeem script (P2SH)
                if txi_sign.script_type == InputScriptType.SPENDMULTISIG:
                    txi_sign.script_sig = scripts.output_script_multisig(
                        multisig.multisig_get_pubkeys(txi_sign.multisig),
                        txi_sign.multisig.m,
                    )
                elif txi_sign.script_type == InputScriptType.SPENDADDRESS:
                    txi_sign.script_sig = scripts.output_script_p2pkh(
                        addresses.ecdsa_hash_pubkey(key_sign_pub, self.coin)
                    )
                else:
                    raise SigningError(
                        FailureType.ProcessError, "Unknown transaction type"
                    )
            else:
                txi.script_sig = bytes()
            self.write_tx_input(h_sign, txi)

        writers.write_varint(h_sign, self.tx.outputs_count)

        txo_bin = TxOutputBinType()
        for i in range(self.tx.outputs_count):
            # STAGE_REQUEST_4_OUTPUT
            txo = await helpers.request_tx_output(self.tx_req, i, self.coin)
            txo_bin.amount = txo.amount
            txo_bin.script_pubkey = self.output_derive_script(txo)
            writers.write_tx_output(h_check, txo_bin)
            writers.write_tx_output(h_sign, txo_bin)

        writers.write_uint32(h_sign, self.tx.lock_time)
        writers.write_uint32(h_sign, self.get_hash_type())

        # check the control digests
        if self.h_confirmed.get_digest() != h_check.get_digest():
            raise SigningError(
                FailureType.ProcessError, "Transaction has changed during signing"
            )

        # if multisig, check if signing with a key that is included in multisig
        if txi_sign.multisig:
            multisig.multisig_pubkey_index(txi_sign.multisig, key_sign_pub)

        # compute the signature from the tx digest
        signature = ecdsa_sign(
            key_sign, writers.get_tx_hash(h_sign, double=self.coin.sign_hash_double)
        )

        # serialize input with correct signature
        gc.collect()
        txi_sign.script_sig = self.input_derive_script(
            txi_sign, key_sign_pub, signature
        )
        w_txi_sign = writers.empty_bytearray(
            5 + len(txi_sign.prev_hash) + 4 + len(txi_sign.script_sig) + 4
        )
        if i_sign == 0:  # serializing first input => prepend headers
            self.write_sign_tx_header(w_txi_sign, True in self.segwit.values())
        self.write_tx_input(w_txi_sign, txi_sign)

        self.tx_ser.signature_index = i_sign
        self.tx_ser.signature = signature
        self.tx_ser.serialized_tx = w_txi_sign
        self.tx_req.serialized = self.tx_ser

    async def serialize_output(self, i: int) -> None:
        # STAGE_REQUEST_5_OUTPUT
        txo = await helpers.request_tx_output(self.tx_req, i, self.coin)
        txo_bin = TxOutputBinType()
        txo_bin.amount = txo.amount
        txo_bin.script_pubkey = self.output_derive_script(txo)

        w_txo_bin = writers.empty_bytearray(5 + 8 + 5 + len(txo_bin.script_pubkey) + 4)
        if i == 0:  # serializing first output => prepend outputs count
            writers.write_varint(w_txo_bin, self.tx.outputs_count)
        writers.write_tx_output(w_txo_bin, txo_bin)

        self.tx_ser.signature_index = None
        self.tx_ser.signature = None
        self.tx_ser.serialized_tx = w_txo_bin
        self.tx_req.serialized = self.tx_ser

    async def get_prevtx_output_value(self, prev_hash: bytes, prev_index: int) -> int:
        amount_out = 0  # output amount

        # STAGE_REQUEST_2_PREV_META
        tx = await helpers.request_tx_meta(self.tx_req, self.coin, prev_hash)

        if tx.outputs_cnt <= prev_index:
            raise SigningError(
                FailureType.ProcessError, "Not enough outputs in previous transaction."
            )

        txh = self.create_hash_writer()

        # TODO set has_segwit correctly
        self.write_tx_header(txh, tx, has_segwit=False)
        writers.write_varint(txh, tx.inputs_cnt)

        for i in range(tx.inputs_cnt):
            # STAGE_REQUEST_2_PREV_INPUT
            txi = await helpers.request_tx_input(self.tx_req, i, self.coin, prev_hash)
            self.write_tx_input(txh, txi)

        writers.write_varint(txh, tx.outputs_cnt)

        for o in range(tx.outputs_cnt):
            # STAGE_REQUEST_2_PREV_OUTPUT
            txo_bin = await helpers.request_tx_output(
                self.tx_req, o, self.coin, prev_hash
            )
            writers.write_tx_output(txh, txo_bin)
            if o == prev_index:
                amount_out = txo_bin.amount
                self.check_prevtx_output(txo_bin)

        await self.write_prev_tx_footer(txh, tx, prev_hash)

        if (
            writers.get_tx_hash(txh, double=self.coin.sign_hash_double, reverse=True)
            != prev_hash
        ):
            raise SigningError(
                FailureType.ProcessError, "Encountered invalid prev_hash"
            )

        return amount_out

    def check_prevtx_output(self, txo_bin: TxOutputBinType) -> None:
        pass

    # TX Helpers
    # ===

    def get_hash_type(self) -> int:
        SIGHASH_ALL = const(0x01)
        return SIGHASH_ALL

    def write_tx_input(self, w: writers.Writer, i: TxInputType) -> None:
        writers.write_tx_input(w, i)

    def write_sign_tx_header(self, w: writers.Writer, has_segwit: bool) -> None:
        self.write_tx_header(w, self.tx, has_segwit)
        writers.write_varint(w, self.tx.inputs_count)

    def write_sign_tx_footer(self, w: writers.Writer) -> None:
        writers.write_uint32(w, self.tx.lock_time)

    def write_tx_header(
        self, w: writers.Writer, tx: Union[SignTx, TransactionType], has_segwit: bool
    ) -> None:
        writers.write_uint32(w, tx.version)  # nVersion
        if has_segwit:
            writers.write_varint(w, 0x00)  # segwit witness marker
            writers.write_varint(w, 0x01)  # segwit witness flag

    async def write_prev_tx_footer(
        self, w: writers.Writer, tx: TransactionType, prev_hash: bytes
    ) -> None:
        writers.write_uint32(w, tx.lock_time)

    # TX Outputs
    # ===

    def output_derive_script(self, o: TxOutputType) -> bytes:
        if o.script_type == OutputScriptType.PAYTOOPRETURN:
            return scripts.output_script_paytoopreturn(o.op_return_data)

        if o.address_n:
            # change output
            o.address = self.get_address_for_change(o)

        if self.coin.bech32_prefix and o.address.startswith(self.coin.bech32_prefix):
            # p2wpkh or p2wsh
            witprog = addresses.decode_bech32_address(
                self.coin.bech32_prefix, o.address
            )
            return scripts.output_script_native_p2wpkh_or_p2wsh(witprog)

        raw_address = self.get_raw_address(o)

        if address_type.check(self.coin.address_type, raw_address):
            # p2pkh
            pubkeyhash = address_type.strip(self.coin.address_type, raw_address)
            script = scripts.output_script_p2pkh(pubkeyhash)
            return script

        elif address_type.check(self.coin.address_type_p2sh, raw_address):
            # p2sh
            scripthash = address_type.strip(self.coin.address_type_p2sh, raw_address)
            script = scripts.output_script_p2sh(scripthash)
            return script

        raise SigningError(FailureType.DataError, "Invalid address type")

    def get_raw_address(self, o: TxOutputType) -> bytes:
        try:
            return base58.decode_check(o.address, self.coin.b58_hash)
        except ValueError:
            raise SigningError(FailureType.DataError, "Invalid address")

    def get_address_for_change(self, o: TxOutputType) -> str:
        try:
            input_script_type = helpers.CHANGE_OUTPUT_TO_INPUT_SCRIPT_TYPES[
                o.script_type
            ]
        except KeyError:
            raise SigningError(FailureType.DataError, "Invalid script type")
        node = self.keychain.derive(o.address_n, self.coin.curve_name)
        return addresses.get_address(input_script_type, self.coin, node, o.multisig)

    def output_is_change(self, o: TxOutputType) -> bool:
        if o.script_type not in helpers.CHANGE_OUTPUT_SCRIPT_TYPES:
            return False
        if o.multisig and not self.multisig_fp.matches(o.multisig):
            return False
        return (
            self.wallet_path is not None
            and self.wallet_path == o.address_n[:-_BIP32_WALLET_DEPTH]
            and o.address_n[-2] <= _BIP32_CHANGE_CHAIN
            and o.address_n[-1] <= _BIP32_MAX_LAST_ELEMENT
        )

    # Tx Inputs
    # ===

    def input_derive_script(
        self, i: TxInputType, pubkey: bytes, signature: bytes = None
    ) -> bytes:
        if i.script_type == InputScriptType.SPENDADDRESS:
            # p2pkh or p2sh
            return scripts.input_script_p2pkh_or_p2sh(
                pubkey, signature, self.get_hash_type()
            )

        if i.script_type == InputScriptType.SPENDP2SHWITNESS:
            # p2wpkh or p2wsh using p2sh

            if i.multisig:
                # p2wsh in p2sh
                pubkeys = multisig.multisig_get_pubkeys(i.multisig)
                witness_script_hasher = self.create_hash_writer()
                scripts.write_output_script_multisig(
                    witness_script_hasher, pubkeys, i.multisig.m
                )
                witness_script_hash = witness_script_hasher.get_digest()
                return scripts.input_script_p2wsh_in_p2sh(witness_script_hash)

            # p2wpkh in p2sh
            return scripts.input_script_p2wpkh_in_p2sh(
                addresses.ecdsa_hash_pubkey(pubkey, self.coin)
            )
        elif i.script_type == InputScriptType.SPENDWITNESS:
            # native p2wpkh or p2wsh
            return scripts.input_script_native_p2wpkh_or_p2wsh()
        elif i.script_type == InputScriptType.SPENDMULTISIG:
            # p2sh multisig
            signature_index = multisig.multisig_pubkey_index(i.multisig, pubkey)
            return scripts.input_script_multisig(
                i.multisig, signature, signature_index, self.get_hash_type(), self.coin
            )
        else:
            raise SigningError(FailureType.ProcessError, "Invalid script type")

    def input_extract_wallet_path(self, txi: TxInputType) -> None:
        if self.wallet_path is None:
            return  # there was a mismatch in previous inputs
        address_n = txi.address_n[:-_BIP32_WALLET_DEPTH]
        if not address_n:
            self.wallet_path = None  # input path is too short
        elif not self.wallet_path:
            self.wallet_path = address_n  # this is the first input
        elif self.wallet_path != address_n:
            self.wallet_path = None  # paths don't match

    def input_check_wallet_path(self, txi: TxInputType) -> None:
        if self.wallet_path is None:
            return  # there was a mismatch in Step 1, ignore it now
        address_n = txi.address_n[:-_BIP32_WALLET_DEPTH]
        if self.wallet_path != address_n:
            raise SigningError(
                FailureType.ProcessError, "Transaction has changed during signing"
            )

    def input_check_multisig_fingerprint(self, txi: TxInputType) -> None:
        if self.multisig_fp.mismatch is False:
            # All inputs in Step 1 had matching multisig fingerprints, allowing a multisig change-output.
            if not txi.multisig or not self.multisig_fp.matches(txi.multisig):
                # This input no longer has a matching multisig fingerprint.
                raise SigningError(
                    FailureType.ProcessError, "Transaction has changed during signing"
                )


def input_is_segwit(i: TxInputType) -> bool:
    return (
        i.script_type == InputScriptType.SPENDWITNESS
        or i.script_type == InputScriptType.SPENDP2SHWITNESS
    )


def ecdsa_sign(node: bip32.HDNode, digest: bytes) -> bytes:
    sig = secp256k1.sign(node.private_key(), digest)
    sigder = der.encode_seq((sig[1:33], sig[33:65]))
    return sigder