def _check_subaddresses(
state: State,
outputs: list[MoneroTransactionDestinationEntry]) -> None:
"""
Using subaddresses leads to a few poorly documented exceptions.
Normally we set R=r*G (tx_pub), however for subaddresses this is equal to R=r*D
to achieve the nice blockchain scanning property.
Remember, that R is per-transaction and not per-input. It's all good if we have a
single output or we have a single destination and the second output is our change.
This is because although the R=r*D, we can still derive the change using our private view-key.
In other words, calculate the one-time address as P = H(x*R)*G + Y (where X,Y is the change).
However, this does not work for other outputs than change, because we do not have the
recipient's view key, so we cannot use the same formula -- we need a new R.
The solution is very straightforward -- we create additional `R`s and use the `extra`
field to include them under the `ADDITIONAL_PUBKEYS` tag.
See:
- https://lab.getmonero.org/pubs/MRL-0006.pdf
- https://github.com/monero-project/monero/pull/2056
"""
from apps.monero.xmr.addresses import classify_subaddresses
# let's first figure out what kind of destinations we have
num_stdaddresses, num_subaddresses, single_dest_subaddress = classify_subaddresses(
outputs, state.change_address())
# if this is a single-destination transfer to a subaddress,
# we set (override) the tx pubkey to R=r*D and no additional
# tx keys are needed
if num_stdaddresses == 0 and num_subaddresses == 1:
state.tx_pub = crypto.scalarmult_into(
None,
crypto_helpers.decodepoint(
single_dest_subaddress.spend_public_key),
state.tx_priv,
)
# if a subaddress is used and either standard address is as well
# or more than one subaddress is used we need to add additional tx keys
state.need_additional_txkeys = num_subaddresses > 0 and (
num_stdaddresses > 0 or num_subaddresses > 1)
state.mem_trace(4, True)
async def init_transaction(
state: State,
address_n: list,
network_type: int,
tsx_data: MoneroTransactionData,
keychain,
) -> MoneroTransactionInitAck:
from apps.monero.signing import offloading_keys
from apps.common import paths
await paths.validate_path(state.ctx, misc.validate_full_path, keychain,
address_n, CURVE)
state.creds = misc.get_creds(keychain, address_n, network_type)
state.client_version = tsx_data.client_version or 0
if state.client_version == 0:
raise ValueError("Client version not supported")
state.fee = state.fee if state.fee > 0 else 0
state.tx_priv = crypto.random_scalar()
state.tx_pub = crypto.scalarmult_base(state.tx_priv)
state.mem_trace(1)
state.input_count = tsx_data.num_inputs
state.output_count = len(tsx_data.outputs)
state.progress_total = 4 + 3 * state.input_count + state.output_count
state.progress_cur = 0
# Ask for confirmation
await confirms.require_confirm_transaction(state.ctx, state, tsx_data,
state.creds.network_type)
state.creds.address = None
state.creds.network_type = None
gc.collect()
state.mem_trace(3)
# Basic transaction parameters
state.output_change = tsx_data.change_dts
state.mixin = tsx_data.mixin
state.fee = tsx_data.fee
state.account_idx = tsx_data.account
state.last_step = state.STEP_INIT
if tsx_data.hard_fork:
state.hard_fork = tsx_data.hard_fork
# Ensure change is correct
_check_change(state, tsx_data.outputs)
# At least two outpus are required, this applies also for sweep txs
# where one fake output is added. See _check_change for more info
if state.output_count < 2:
raise signing.NotEnoughOutputsError(
"At least two outputs are required")
_check_rsig_data(state, tsx_data.rsig_data)
_check_subaddresses(state, tsx_data.outputs)
# Extra processing, payment id
_process_payment_id(state, tsx_data)
await _compute_sec_keys(state, tsx_data)
gc.collect()
# Iterative tx_prefix_hash hash computation
state.tx_prefix_hasher.uvarint(
2) # current Monero transaction format (RingCT = 2)
state.tx_prefix_hasher.uvarint(tsx_data.unlock_time)
state.tx_prefix_hasher.uvarint(state.input_count) # ContainerType, size
state.mem_trace(10, True)
# Final message hasher
state.full_message_hasher.init()
state.full_message_hasher.set_type_fee(signing.RctType.Bulletproof2,
state.fee)
# Sub address precomputation
if tsx_data.account is not None and tsx_data.minor_indices:
_precompute_subaddr(state, tsx_data.account, tsx_data.minor_indices)
state.mem_trace(5, True)
# HMACs all outputs to disallow tampering.
# Each HMAC is then sent alongside the output
# and trezor validates it.
hmacs = []
for idx in range(state.output_count):
c_hmac = await offloading_keys.gen_hmac_tsxdest(
state.key_hmac, tsx_data.outputs[idx], idx)
hmacs.append(c_hmac)
gc.collect()
state.mem_trace(6)
from trezor.messages.MoneroTransactionInitAck import MoneroTransactionInitAck
from trezor.messages.MoneroTransactionRsigData import MoneroTransactionRsigData
rsig_data = MoneroTransactionRsigData(offload_type=state.rsig_offload)
return MoneroTransactionInitAck(hmacs=hmacs, rsig_data=rsig_data)
