refactor(core/ethereum): simplify `sign_tx_eip1559()` digest flow
What the developer wrote
Authored by Roman Zeyde
refactor(core/ethereum): simplify `sign_tx_eip1559()` digest flow
De-duplicate RLP `fields` definition and better encapsulate RLP length
and digest computation - see `_start_digest` and `_finish_digest`.
[no changelog]
What changed, and why it matters
This commit is a code cleanup (refactor) for how Trezor's Ethereum app builds the transaction hash for EIP-1559 transactions. It moves the existing hashing steps into two helper functions and removes a duplicated list of transaction fields. There is no change to what data is signed or how it is signed, and no security bug is introduced or fixed.
No security action needed. Treat as a normal maintainability refactor. If reviewing, verify that the field order in `_start_digest()` matches the original inline order and the EIP-1559 RLP encoding specification: chain_id, nonce, max_priority_fee_per_gas, max_fee_per_gas, gas_limit, to, value, data, access_list.
Security signals we found
No strong security signals were identified.
Evidence from the diff
The change refactors sign_tx_eip1559() in core/src/apps/ethereum/sign_tx_eip1559.py. It extracts the digest construction into _start_digest() and _finish_digest(). _start_digest() now defines the RLP field list once, computes the total RLP length (fields + calldata header/length + access list), writes the transaction type byte, RLP list header, and the static fields into the keccak256 hash, and returns the HashWriter. _finish_digest() streams the access list into the same hash and returns the final digest. The previous inline code did the same operations but duplicated the field list and split length computation across _get_digest_length() and the main function. The commit is tagged [no changelog].
Changed components
core/src/apps/ethereum/sign_tx_eip1559.pyInspect captured patch +35 / −38
### core/src/apps/ethereum/sign_tx_eip1559.py
@@ -12,6 +12,7 @@
EthereumSignTxEIP1559,
EthereumTxRequest,
)
+ from trezor.utils import HashWriter
from apps.common.keychain import Keychain
@@ -32,12 +33,11 @@ async def sign_tx_eip1559(
defs: Definitions,
) -> EthereumTxRequest:
from trezor import TR, wire
- from trezor.crypto import rlp # local_cache_global
from trezor.ui.layouts import show_continue_in_app
from apps.common import paths
- from .helpers import format_ethereum_amount, get_fee_items_eip1559, keccak256
+ from .helpers import format_ethereum_amount, get_fee_items_eip1559
from .sign_tx import (
check_common_fields,
confirm_tx_data,
@@ -79,23 +79,7 @@ async def sign_tx_eip1559(
msg.payment_req, slip44_id, keychain, amount_size_bytes=32
)
- sha = keccak256()
-
- rlp.write(sha, _TX_TYPE)
- rlp.write_header(sha, _get_digest_length(msg), rlp.LIST_HEADER_BYTE)
-
- fields: tuple[rlp.RLPItem, ...] = (
- msg.chain_id,
- msg.nonce,
- msg.max_priority_fee,
- msg.max_gas_fee,
- gas_limit,
- address_bytes,
- msg.value,
- )
- for field in fields:
- rlp.write(sha, field)
-
+ sha = _start_digest(msg)
initial_data = await request_initial_data(msg, sha)
# Confirm the transaction, using special layouts for staking, yielding and clear-signing (if supported).
@@ -112,13 +96,7 @@ async def sign_tx_eip1559(
create_data_chunk_loader(sha),
)
- # write_access_list (streaming instead of full materialization)
- payload_length = sum(rlp.length(access_list_item(i)) for i in msg.access_list)
- rlp.write_header(sha, payload_length, rlp.LIST_HEADER_BYTE)
- for item in msg.access_list:
- rlp.write(sha, access_list_item(item))
-
- digest = sha.get_digest()
+ digest = _finish_digest(msg, sha)
# transaction data confirmed, proceed with signing
result = _sign_digest(msg, keychain, digest)
@@ -127,31 +105,50 @@ async def sign_tx_eip1559(
return result
-def _get_digest_length(msg: EthereumSignTxEIP1559) -> int:
- length = 0
+def _start_digest(msg: EthereumSignTxEIP1559) -> HashWriter:
+ from .helpers import keccak256
fields: tuple[rlp.RLPItem, ...] = (
+ msg.chain_id,
msg.nonce,
+ msg.max_priority_fee,
+ msg.max_gas_fee,
msg.gas_limit,
bytes_from_address(msg.to),
msg.value,
- msg.chain_id,
- msg.max_gas_fee,
- msg.max_priority_fee,
)
- for field in fields:
- length += rlp.length(field)
- data_length = msg.data_length
- length += rlp.header_length(data_length, msg.data_initial_chunk)
- length += data_length
+ # fields length
+ length = sum(rlp.length(field) for field in fields)
+
+ # calldata length
+ length += rlp.header_length(msg.data_length, msg.data_initial_chunk)
+ length += msg.data_length
- # access_list_length
+ # access_list length (streaming instead of full materialization)
payload_length = sum(rlp.length(access_list_item(i)) for i in msg.access_list)
access_list_length = rlp.header_length(payload_length) + payload_length
length += access_list_length
- return length
+ # hash only `_TX_TYPE`, RLP header and `fields` (see above).
+ # calldata and access_list will be hashed later.
+ sha = keccak256()
+
+ rlp.write(sha, _TX_TYPE)
+ rlp.write_header(sha, length, rlp.LIST_HEADER_BYTE)
+ for field in fields:
+ rlp.write(sha, field)
+ return sha
+
+
+def _finish_digest(msg: EthereumSignTxEIP1559, sha: HashWriter) -> bytes:
+ # write_access list (streaming instead of full materialization)
+ payload_length = sum(rlp.length(access_list_item(i)) for i in msg.access_list)
+ rlp.write_header(sha, payload_length, rlp.LIST_HEADER_BYTE)
+ for item in msg.access_list:
+ rlp.write(sha, access_list_item(item))
+
+ return sha.get_digest()
def _sign_digest(Why this scored 12/100
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