core: introduce safer write_bytes functions

core/src/apps/common/writers.py

@@ -78,11 +78,18 @@ def write_uint64_be(w: Writer, n: int) -> int:
     return 8
 
 
-def write_bytes(w: Writer, b: bytes) -> int:
+def write_bytes_unchecked(w: Writer, b: bytes) -> int:
     w.extend(b)
     return len(b)
 
 
-def write_bytes_reversed(w: Writer, b: bytes) -> int:
+def write_bytes_fixed(w: Writer, b: bytes, length: int) -> int:
+    ensure(len(b) == length)
+    w.extend(b)
+    return length
+
+
+def write_bytes_reversed(w: Writer, b: bytes, length: int) -> int:
+    ensure(len(b) == length)
     w.extend(bytes(reversed(b)))
-    return len(b)
+    return length

core/src/apps/eos/actions/__init__.py

@@ -68,7 +68,7 @@ async def process_action(
 
     writers.write_action_common(sha, action.common)
     writers.write_variant32(sha, len(w))
-    writers.write_bytes(sha, w)
+    writers.write_bytes_unchecked(sha, w)
 
 
 async def process_unknown_action(
@@ -78,7 +78,7 @@ async def process_unknown_action(
     writers.write_variant32(checksum, action.unknown.data_size)
     checksum.extend(action.unknown.data_chunk)
 
-    writers.write_bytes(w, action.unknown.data_chunk)
+    writers.write_bytes_unchecked(w, action.unknown.data_chunk)
     bytes_left = action.unknown.data_size - len(action.unknown.data_chunk)
 
     while bytes_left != 0:
@@ -90,7 +90,7 @@ async def process_unknown_action(
             raise ValueError("Bad response. Unknown struct expected.")
 
         checksum.extend(action.unknown.data_chunk)
-        writers.write_bytes(w, action.unknown.data_chunk)
+        writers.write_bytes_unchecked(w, action.unknown.data_chunk)
 
         bytes_left -= len(action.unknown.data_chunk)
         if bytes_left < 0:

core/src/apps/eos/sign_tx.py

@@ -34,7 +34,7 @@ async def sign_tx(
     await _init(ctx, sha, msg)
     await _actions(ctx, sha, msg.num_actions)
     writers.write_variant32(sha, 0)
-    writers.write_bytes(sha, bytearray(32))
+    writers.write_bytes_unchecked(sha, bytearray(32))
 
     digest = sha.get_digest()
     signature = secp256k1.sign(
@@ -45,7 +45,7 @@ async def sign_tx(
 
 
 async def _init(ctx: wire.Context, sha: HashWriter, msg: EosSignTx) -> None:
-    writers.write_bytes(sha, msg.chain_id)
+    writers.write_bytes_unchecked(sha, msg.chain_id)
     writers.write_header(sha, msg.header)
     writers.write_variant32(sha, 0)
     writers.write_variant32(sha, msg.num_actions)

core/src/apps/eos/writers.py

@@ -1,5 +1,5 @@
 from apps.common.writers import (
-    write_bytes,
+    write_bytes_unchecked,
     write_uint8,
     write_uint16_le,
     write_uint32_le,
@@ -31,7 +31,7 @@ def write_auth(w: Writer, auth: EosAuthorization) -> None:
     write_variant32(w, len(auth.keys))
     for key in auth.keys:
         write_variant32(w, key.type)
-        write_bytes(w, key.key)
+        write_bytes_unchecked(w, key.key)
         write_uint16_le(w, key.weight)
 
     write_variant32(w, len(auth.accounts))
@@ -60,7 +60,7 @@ def write_action_transfer(w: Writer, msg: EosActionTransfer) -> None:
     write_uint64_le(w, msg.receiver)
     write_asset(w, msg.quantity)
     write_variant32(w, len(msg.memo))
-    write_bytes(w, msg.memo)
+    write_bytes_unchecked(w, msg.memo)
 
 
 def write_action_buyram(w: Writer, msg: EosActionBuyRam) -> None:
@@ -162,4 +162,4 @@ def write_variant32(w: Writer, value: int) -> None:
         variant.append(b)
         if value == 0:
             break
-    write_bytes(w, bytes(variant))
+    write_bytes_unchecked(w, bytes(variant))

core/src/apps/nem/writers.py

@@ -1,6 +1,6 @@
 from trezor.messages.NEMTransactionCommon import NEMTransactionCommon
 
-from apps.common.writers import write_bytes, write_uint32_le, write_uint64_le
+from apps.common.writers import write_bytes_unchecked, write_uint32_le, write_uint64_le
 
 
 def serialize_tx_common(
@@ -26,4 +26,4 @@ def serialize_tx_common(
 
 def write_bytes_with_len(w, buf: bytes):
     write_uint32_le(w, len(buf))
-    write_bytes(w, buf)
+    write_bytes_unchecked(w, buf)

core/src/apps/stellar/operations/serialize.py

@@ -119,7 +119,7 @@ def write_set_options_op(w, msg: StellarSetOptionsOp):
     elif msg.signer_type in consts.SIGN_TYPES:
         writers.write_bool(w, True)
         writers.write_uint32(w, msg.signer_type)
-        writers.write_bytes(w, msg.signer_key)
+        writers.write_bytes_unchecked(w, msg.signer_key)
         writers.write_uint32(w, msg.signer_weight)
     else:
         raise ProcessError("Stellar: unknown signer type")
@@ -146,10 +146,10 @@ def _write_asset_code(w, asset_type: int, asset_code: str):
         return  # nothing is needed
     elif asset_type == consts.ASSET_TYPE_ALPHANUM4:
         # pad with zeros to 4 chars
-        writers.write_bytes(w, code + bytearray([0] * (4 - len(code))))
+        writers.write_bytes_unchecked(w, code + bytearray([0] * (4 - len(code))))
     elif asset_type == consts.ASSET_TYPE_ALPHANUM12:
         # pad with zeros to 12 chars
-        writers.write_bytes(w, code + bytearray([0] * (12 - len(code))))
+        writers.write_bytes_unchecked(w, code + bytearray([0] * (12 - len(code))))
     else:
         raise ProcessError("Stellar: invalid asset type")
 

core/src/apps/stellar/sign_tx.py

@@ -47,8 +47,8 @@ async def _final(ctx, w: bytearray, msg: StellarSignTx):
 
 async def _init(ctx, w: bytearray, pubkey: bytes, msg: StellarSignTx):
     network_passphrase_hash = sha256(msg.network_passphrase).digest()
-    writers.write_bytes(w, network_passphrase_hash)
-    writers.write_bytes(w, consts.TX_TYPE)
+    writers.write_bytes_unchecked(w, network_passphrase_hash)
+    writers.write_bytes_unchecked(w, consts.TX_TYPE)
 
     address = helpers.address_from_public_key(pubkey)
     accounts_match = msg.source_account == address
@@ -103,7 +103,7 @@ async def _memo(ctx, w: bytearray, msg: StellarSignTx):
         memo_confirm_text = str(msg.memo_id)
     elif msg.memo_type in (consts.MEMO_TYPE_HASH, consts.MEMO_TYPE_RETURN):
         # Hash/Return: 32 byte hash
-        writers.write_bytes(w, bytearray(msg.memo_hash))
+        writers.write_bytes_unchecked(w, bytearray(msg.memo_hash))
         memo_confirm_text = hexlify(msg.memo_hash).decode()
     else:
         raise ProcessError("Stellar invalid memo type")

core/src/apps/stellar/writers.py

@@ -1,6 +1,6 @@
 from .helpers import public_key_from_address
 
-from apps.common.writers import write_bytes, write_uint32_be, write_uint64_be
+from apps.common.writers import write_bytes_unchecked, write_uint32_be, write_uint64_be
 
 write_uint32 = write_uint32_be
 write_uint64 = write_uint64_be
@@ -16,11 +16,11 @@ def write_string(w, s: AnyStr) -> None:
     else:
         buf = s
     write_uint32(w, len(buf))
-    write_bytes(w, buf)
+    write_bytes_unchecked(w, buf)
     # if len isn't a multiple of 4, add padding bytes
     reminder = len(buf) % 4
     if reminder:
-        write_bytes(w, bytes([0] * (4 - reminder)))
+        write_bytes_unchecked(w, bytes([0] * (4 - reminder)))
 
 
 def write_bool(w, val: bool):
@@ -33,4 +33,4 @@ def write_bool(w, val: bool):
 def write_pubkey(w, address: str):
     # first 4 bytes of an address are the type, there's only one type (0)
     write_uint32(w, 0)
-    write_bytes(w, public_key_from_address(address))
+    write_bytes_unchecked(w, public_key_from_address(address))

core/src/apps/tezos/helpers.py

@@ -3,7 +3,7 @@ from micropython import const
 from trezor.crypto import base58
 
 from apps.common import HARDENED
-from apps.common.writers import write_uint8, write_bytes
+from apps.common.writers import write_bytes_unchecked, write_uint8
 
 TEZOS_AMOUNT_DECIMALS = const(6)
 TEZOS_ED25519_ADDRESS_PREFIX = "tz1"
@@ -99,4 +99,4 @@ def write_bool(w: bytearray, boolean: bool):
 
 
 def write_instruction(w: bytearray, instruction: str) -> int:
-    write_bytes(w, MICHELSON_INSTRUCTION_BYTES[instruction])
+    write_bytes_unchecked(w, MICHELSON_INSTRUCTION_BYTES[instruction])

core/src/apps/tezos/sign_tx.py

@@ -7,7 +7,7 @@ from trezor.messages import TezosBallotType, TezosContractType
 from trezor.messages.TezosSignedTx import TezosSignedTx
 
 from apps.common import paths
-from apps.common.writers import write_bytes, write_uint8, write_uint32_be
+from apps.common.writers import write_bytes_unchecked, write_uint8, write_uint32_be
 from apps.tezos import CURVE, helpers, layout
 
 PROPOSAL_LENGTH = const(32)
@@ -157,13 +157,13 @@ def _get_ballot(ballot):
 
 
 def _get_operation_bytes(w: bytearray, msg):
-    write_bytes(w, msg.branch)
+    write_bytes_unchecked(w, msg.branch)
 
     # when the account sends first operation in lifetime,
     # we need to reveal its public key
     if msg.reveal is not None:
         _encode_common(w, msg.reveal, "reveal")
-        write_bytes(w, msg.reveal.public_key)
+        write_bytes_unchecked(w, msg.reveal.public_key)
 
     # transaction operation
     if msg.transaction is not None:
@@ -194,7 +194,7 @@ def _get_operation_bytes(w: bytearray, msg):
         _encode_common(w, msg.origination, "origination")
         _encode_zarith(w, msg.origination.balance)
         _encode_data_with_bool_prefix(w, msg.origination.delegate)
-        write_bytes(w, msg.origination.script)
+        write_bytes_unchecked(w, msg.origination.script)
 
     # delegation operation
     elif msg.delegation is not None:
@@ -214,7 +214,7 @@ def _encode_common(w: bytearray, operation, str_operation):
         "delegation": 110,
     }
     write_uint8(w, operation_tags[str_operation])
-    write_bytes(w, operation.source)
+    write_bytes_unchecked(w, operation.source)
     _encode_zarith(w, operation.fee)
     _encode_zarith(w, operation.counter)
     _encode_zarith(w, operation.gas_limit)
@@ -223,13 +223,13 @@ def _encode_common(w: bytearray, operation, str_operation):
 
 def _encode_contract_id(w: bytearray, contract_id):
     write_uint8(w, contract_id.tag)
-    write_bytes(w, contract_id.hash)
+    write_bytes_unchecked(w, contract_id.hash)
 
 
 def _encode_data_with_bool_prefix(w: bytearray, data):
     if data:
         helpers.write_bool(w, True)
-        write_bytes(w, data)
+        write_bytes_unchecked(w, data)
     else:
         helpers.write_bool(w, False)
 
@@ -250,20 +250,20 @@ def _encode_proposal(w: bytearray, proposal):
     proposal_tag = 5
 
     write_uint8(w, proposal_tag)
-    write_bytes(w, proposal.source)
+    write_bytes_unchecked(w, proposal.source)
     write_uint32_be(w, proposal.period)
     write_uint32_be(w, len(proposal.proposals) * PROPOSAL_LENGTH)
     for proposal_hash in proposal.proposals:
-        write_bytes(w, proposal_hash)
+        write_bytes_unchecked(w, proposal_hash)
 
 
 def _encode_ballot(w: bytearray, ballot):
     ballot_tag = 6
 
     write_uint8(w, ballot_tag)
-    write_bytes(w, ballot.source)
+    write_bytes_unchecked(w, ballot.source)
     write_uint32_be(w, ballot.period)
-    write_bytes(w, ballot.proposal)
+    write_bytes_unchecked(w, ballot.proposal)
     write_uint8(w, ballot.ballot)
 
 
@@ -304,7 +304,7 @@ def _encode_manager_common(w: bytearray, sequence_length, operation, to_contract
     else:
         helpers.write_instruction(w, "key_hash")
     if operation == "PUSH":
-        write_bytes(w, bytes([10]))  # byte sequence
+        write_bytes_unchecked(w, bytes([10]))  # byte sequence
         if to_contract is True:
             write_uint32_be(w, SMART_CONTRACT_ADDRESS_LENGTH)
         else:
@@ -319,7 +319,7 @@ def _encode_manager_to_implicit_transfer(w: bytearray, manager_transfer):
     sequence_length = MICHELSON_LENGTH + len(value_natural)
 
     _encode_manager_common(w, sequence_length, "PUSH")
-    write_bytes(w, manager_transfer.destination.hash)
+    write_bytes_unchecked(w, manager_transfer.destination.hash)
     helpers.write_instruction(w, "IMPLICIT_ACCOUNT")
     helpers.write_instruction(w, "PUSH")
     helpers.write_instruction(w, "mutez")
@@ -334,7 +334,7 @@ def _encode_manager_delegation(w: bytearray, delegate):
     MICHELSON_LENGTH = 42  # length is fixed this time(no variable length fields)
 
     _encode_manager_common(w, MICHELSON_LENGTH, "PUSH")
-    write_bytes(w, delegate)
+    write_bytes_unchecked(w, delegate)
     helpers.write_instruction(w, "SOME")
     helpers.write_instruction(w, "SET_DELEGATE")
     helpers.write_instruction(w, "CONS")

core/src/apps/wallet/sign_tx/multisig.py

@@ -5,7 +5,7 @@ from trezor.messages.HDNodeType import HDNodeType
 from trezor.messages.MultisigRedeemScriptType import MultisigRedeemScriptType
 from trezor.utils import HashWriter, ensure
 
-from apps.wallet.sign_tx.writers import write_bytes, write_uint32
+from apps.wallet.sign_tx.writers import write_bytes_unchecked, write_uint32
 
 
 class MultisigError(ValueError):
@@ -59,8 +59,8 @@ def multisig_fingerprint(multisig: MultisigRedeemScriptType) -> bytes:
         write_uint32(h, d.depth)
         write_uint32(h, d.fingerprint)
         write_uint32(h, d.child_num)
-        write_bytes(h, d.chain_code)
-        write_bytes(h, d.public_key)
+        write_bytes_unchecked(h, d.chain_code)
+        write_bytes_unchecked(h, d.public_key)
 
     return h.get_digest()
 

core/src/apps/wallet/sign_tx/scripts.py

@@ -4,7 +4,7 @@ from trezor.messages.MultisigRedeemScriptType import MultisigRedeemScriptType
 from apps.common.coininfo import CoinInfo
 from apps.common.writers import empty_bytearray
 from apps.wallet.sign_tx.multisig import multisig_get_pubkey_count, multisig_get_pubkeys
-from apps.wallet.sign_tx.writers import write_bytes, write_op_push, write_varint
+from apps.wallet.sign_tx.writers import write_bytes_unchecked, write_op_push, write_varint
 
 
 class ScriptsError(ValueError):
@@ -74,7 +74,7 @@ def output_script_native_p2wpkh_or_p2wsh(witprog: bytes) -> bytearray:
     w = empty_bytearray(3 + len(witprog))
     w.append(0x00)  # witness version byte
     w.append(len(witprog))  # pub key hash length is 20 (P2WPKH) or 32 (P2WSH) bytes
-    write_bytes(w, witprog)  # pub key hash
+    write_bytes_unchecked(w, witprog)  # pub key hash
     return w
 
 
@@ -95,7 +95,7 @@ def input_script_p2wpkh_in_p2sh(pubkeyhash: bytes) -> bytearray:
     w.append(0x16)  # length of the data
     w.append(0x00)  # witness version byte
     w.append(0x14)  # P2WPKH witness program (pub key hash length)
-    write_bytes(w, pubkeyhash)  # pub key hash
+    write_bytes_unchecked(w, pubkeyhash)  # pub key hash
     return w
 
 
@@ -118,7 +118,7 @@ def input_script_p2wsh_in_p2sh(script_hash: bytes) -> bytearray:
     w.append(0x22)  # length of the data
     w.append(0x00)  # witness version byte
     w.append(0x20)  # P2WSH witness program (redeem script hash length)
-    write_bytes(w, script_hash)
+    write_bytes_unchecked(w, script_hash)
     return w
 
 
@@ -272,12 +272,12 @@ def output_script_paytoopreturn(data: bytes) -> bytearray:
 
 def append_signature(w: bytearray, signature: bytes, sighash: int) -> bytearray:
     write_op_push(w, len(signature) + 1)
-    write_bytes(w, signature)
+    write_bytes_unchecked(w, signature)
     w.append(sighash)
     return w
 
 
 def append_pubkey(w: bytearray, pubkey: bytes) -> bytearray:
     write_op_push(w, len(pubkey))
-    write_bytes(w, pubkey)
+    write_bytes_unchecked(w, pubkey)
     return w

core/src/apps/wallet/sign_tx/segwit_bip143.py

@@ -10,7 +10,7 @@ from apps.wallet.sign_tx.multisig import multisig_get_pubkeys
 from apps.wallet.sign_tx.scripts import output_script_multisig, output_script_p2pkh
 from apps.wallet.sign_tx.writers import (
     get_tx_hash,
-    write_bytes,
+    write_bytes_unchecked,
     write_bytes_reversed,
     write_tx_output,
     write_uint32,
@@ -61,19 +61,19 @@ class Bip143:
         ensure(not coin.overwintered)
 
         write_uint32(h_preimage, tx.version)  # nVersion
-        write_bytes(h_preimage, self.get_prevouts_hash(coin))  # hashPrevouts
-        write_bytes(h_preimage, self.get_sequence_hash(coin))  # hashSequence
+        write_bytes_unchecked(h_preimage, self.get_prevouts_hash(coin))  # hashPrevouts
+        write_bytes_unchecked(h_preimage, self.get_sequence_hash(coin))  # hashSequence
 
         write_bytes_reversed(h_preimage, txi.prev_hash)  # outpoint
         write_uint32(h_preimage, txi.prev_index)  # outpoint
 
         script_code = self.derive_script_code(txi, pubkeyhash)  # scriptCode
         write_varint(h_preimage, len(script_code))
-        write_bytes(h_preimage, script_code)
+        write_bytes_unchecked(h_preimage, script_code)
 
         write_uint64(h_preimage, txi.amount)  # amount
         write_uint32(h_preimage, txi.sequence)  # nSequence
-        write_bytes(h_preimage, self.get_outputs_hash(coin))  # hashOutputs
+        write_bytes_unchecked(h_preimage, self.get_outputs_hash(coin))  # hashOutputs
         write_uint32(h_preimage, tx.lock_time)  # nLockTime
         write_uint32(h_preimage, sighash)  # nHashType
 

core/src/apps/wallet/sign_tx/signing.py

@@ -151,7 +151,7 @@ async def check_tx_fee(tx: SignTx, keychain: seed.Keychain, coin: coininfo.CoinI
             w_txi = writers.empty_bytearray(8 if i == 0 else 0 + 9 + len(txi.prev_hash))
             if i == 0:  # serializing first input => prepend headers
                 # decred doesn't support segwit
-                writers.write_bytes(w_txi, get_tx_header(coin, tx, False))
+                writers.write_bytes_unchecked(w_txi, get_tx_header(coin, tx, False))
             writers.write_tx_input_decred(w_txi, txi)
             tx_ser.serialized_tx = w_txi
             tx_req.serialized = tx_ser
@@ -281,7 +281,7 @@ async def sign_tx(tx: SignTx, keychain: seed.Keychain):
                 7 + len(txi_sign.prev_hash) + 4 + len(txi_sign.script_sig) + 4
             )
             if i_sign == 0:  # serializing first input => prepend headers
-                writers.write_bytes(w_txi, get_tx_header(coin, tx, True))
+                writers.write_bytes_unchecked(w_txi, get_tx_header(coin, tx, True))
             writers.write_tx_input(w_txi, txi_sign)
             tx_ser.serialized_tx = w_txi
             tx_ser.signature_index = None
@@ -331,7 +331,7 @@ async def sign_tx(tx: SignTx, keychain: seed.Keychain):
                 5 + len(txi_sign.prev_hash) + 4 + len(txi_sign.script_sig) + 4
             )
             if i_sign == 0:  # serializing first input => prepend headers
-                writers.write_bytes(w_txi_sign, get_tx_header(coin, tx, any_segwit))
+                writers.write_bytes_unchecked(w_txi_sign, get_tx_header(coin, tx, any_segwit))
             writers.write_tx_input(w_txi_sign, txi_sign)
             tx_ser.serialized_tx = w_txi_sign
 
@@ -367,7 +367,7 @@ async def sign_tx(tx: SignTx, keychain: seed.Keychain):
             for ii in range(tx.inputs_count):
                 if ii == i_sign:
                     writers.write_varint(h_witness, len(prev_pkscript))
-                    writers.write_bytes(h_witness, prev_pkscript)
+                    writers.write_bytes_unchecked(h_witness, prev_pkscript)
                 else:
                     writers.write_varint(h_witness, 0)
 
@@ -377,8 +377,8 @@ async def sign_tx(tx: SignTx, keychain: seed.Keychain):
 
             h_sign = utils.HashWriter(blake256())
             writers.write_uint32(h_sign, decred.DECRED_SIGHASHALL)
-            writers.write_bytes(h_sign, prefix_hash)
-            writers.write_bytes(h_sign, witness_hash)
+            writers.write_bytes_unchecked(h_sign, prefix_hash)
+            writers.write_bytes_unchecked(h_sign, witness_hash)
 
             sig_hash = writers.get_tx_hash(h_sign, double=coin.sign_hash_double)
             signature = ecdsa_sign(key_sign, sig_hash)
@@ -397,7 +397,9 @@ async def sign_tx(tx: SignTx, keychain: seed.Keychain):
             )
 
             if i_sign == 0:
-                writers.write_bytes(w_txi_sign, hash143.get_last_output_bytes())
+                writers.write_bytes_unchecked(
+                    w_txi_sign, hash143.get_last_output_bytes()
+                )
                 writers.write_uint32(w_txi_sign, tx.lock_time)
                 writers.write_uint32(w_txi_sign, tx.expiry)
                 writers.write_varint(w_txi_sign, tx.inputs_count)
@@ -486,7 +488,7 @@ async def sign_tx(tx: SignTx, keychain: seed.Keychain):
                 5 + len(txi_sign.prev_hash) + 4 + len(txi_sign.script_sig) + 4
             )
             if i_sign == 0:  # serializing first input => prepend headers
-                writers.write_bytes(w_txi_sign, get_tx_header(coin, tx, any_segwit))
+                writers.write_bytes_unchecked(w_txi_sign, get_tx_header(coin, tx, any_segwit))
             writers.write_tx_input(w_txi_sign, txi_sign)
             tx_ser.serialized_tx = w_txi_sign
 
@@ -652,7 +654,7 @@ async def get_prevtx_output_value(
         while ofs < tx.extra_data_len:
             size = min(1024, tx.extra_data_len - ofs)
             data = await helpers.request_tx_extra_data(tx_req, ofs, size, prev_hash)
-            writers.write_bytes(txh, data)
+            writers.write_bytes_unchecked(txh, data)
             ofs += len(data)
 
     if (

core/src/apps/wallet/sign_tx/writers.py

@@ -5,7 +5,7 @@ from trezor.utils import ensure
 
 from apps.common.writers import (  # noqa: F401
     empty_bytearray,
-    write_bytes,
+    write_bytes_unchecked,
     write_bytes_reversed,
     write_uint8,
     write_uint16_le,
@@ -22,12 +22,12 @@ def write_tx_input(w, i: TxInputType):
     write_bytes_reversed(w, i.prev_hash)
     write_uint32(w, i.prev_index)
     write_varint(w, len(i.script_sig))
-    write_bytes(w, i.script_sig)
+    write_bytes_unchecked(w, i.script_sig)
     write_uint32(w, i.sequence)
 
 
 def write_tx_input_check(w, i: TxInputType):
-    write_bytes(w, i.prev_hash)
+    write_bytes_unchecked(w, i.prev_hash)
     write_uint32(w, i.prev_index)
     write_uint32(w, i.script_type)
     write_uint32(w, len(i.address_n))
@@ -49,7 +49,7 @@ def write_tx_input_decred_witness(w, i: TxInputType):
     write_uint32(w, 0)  # block height fraud proof
     write_uint32(w, 0xFFFFFFFF)  # block index fraud proof
     write_varint(w, len(i.script_sig))
-    write_bytes(w, i.script_sig)
+    write_bytes_unchecked(w, i.script_sig)
 
 
 def write_tx_output(w, o: TxOutputBinType):
@@ -57,7 +57,7 @@ def write_tx_output(w, o: TxOutputBinType):
     if o.decred_script_version is not None:
         write_uint16(w, o.decred_script_version)
     write_varint(w, len(o.script_pubkey))
-    write_bytes(w, o.script_pubkey)
+    write_bytes_unchecked(w, o.script_pubkey)
 
 
 def write_op_push(w, n: int):

core/src/apps/wallet/sign_tx/zcash.py

@@ -13,7 +13,7 @@ from apps.wallet.sign_tx.multisig import multisig_get_pubkeys
 from apps.wallet.sign_tx.scripts import output_script_multisig, output_script_p2pkh
 from apps.wallet.sign_tx.writers import (
     get_tx_hash,
-    write_bytes,
+    write_bytes_unchecked,
     write_bytes_reversed,
     write_tx_output,
     write_uint32,
@@ -92,10 +92,10 @@ class Zip143:
             h_preimage, tx.version | OVERWINTERED
         )  # 1. nVersion | fOverwintered
         write_uint32(h_preimage, tx.version_group_id)  # 2. nVersionGroupId
-        write_bytes(h_preimage, bytearray(self.get_prevouts_hash()))  # 3. hashPrevouts
-        write_bytes(h_preimage, bytearray(self.get_sequence_hash()))  # 4. hashSequence
-        write_bytes(h_preimage, bytearray(self.get_outputs_hash()))  # 5. hashOutputs
-        write_bytes(h_preimage, b"\x00" * 32)  # 6. hashJoinSplits
+        write_bytes_unchecked(h_preimage, bytearray(self.get_prevouts_hash()))  # 3. hashPrevouts
+        write_bytes_unchecked(h_preimage, bytearray(self.get_sequence_hash()))  # 4. hashSequence
+        write_bytes_unchecked(h_preimage, bytearray(self.get_outputs_hash()))  # 5. hashOutputs
+        write_bytes_unchecked(h_preimage, b"\x00" * 32)  # 6. hashJoinSplits
         write_uint32(h_preimage, tx.lock_time)  # 7. nLockTime
         write_uint32(h_preimage, tx.expiry)  # 8. expiryHeight
         write_uint32(h_preimage, sighash)  # 9. nHashType
@@ -105,7 +105,7 @@ class Zip143:
 
         script_code = derive_script_code(txi, pubkeyhash)  # 10b. scriptCode
         write_varint(h_preimage, len(script_code))
-        write_bytes(h_preimage, script_code)
+        write_bytes_unchecked(h_preimage, script_code)
 
         write_uint64(h_preimage, txi.amount)  # 10c. value
 
@@ -139,12 +139,12 @@ class Zip243(Zip143):
             h_preimage, tx.version | OVERWINTERED
         )  # 1. nVersion | fOverwintered
         write_uint32(h_preimage, tx.version_group_id)  # 2. nVersionGroupId
-        write_bytes(h_preimage, bytearray(self.get_prevouts_hash()))  # 3. hashPrevouts
-        write_bytes(h_preimage, bytearray(self.get_sequence_hash()))  # 4. hashSequence
-        write_bytes(h_preimage, bytearray(self.get_outputs_hash()))  # 5. hashOutputs
-        write_bytes(h_preimage, b"\x00" * 32)  # 6. hashJoinSplits
-        write_bytes(h_preimage, b"\x00" * 32)  # 7. hashShieldedSpends
-        write_bytes(h_preimage, b"\x00" * 32)  # 8. hashShieldedOutputs
+        write_bytes_unchecked(h_preimage, bytearray(self.get_prevouts_hash()))  # 3. hashPrevouts
+        write_bytes_unchecked(h_preimage, bytearray(self.get_sequence_hash()))  # 4. hashSequence
+        write_bytes_unchecked(h_preimage, bytearray(self.get_outputs_hash()))  # 5. hashOutputs
+        write_bytes_unchecked(h_preimage, b"\x00" * 32)  # 6. hashJoinSplits
+        write_bytes_unchecked(h_preimage, b"\x00" * 32)  # 7. hashShieldedSpends
+        write_bytes_unchecked(h_preimage, b"\x00" * 32)  # 8. hashShieldedOutputs
         write_uint32(h_preimage, tx.lock_time)  # 9. nLockTime
         write_uint32(h_preimage, tx.expiry)  # 10. expiryHeight
         write_uint64(h_preimage, 0)  # 11. valueBalance
@@ -155,7 +155,7 @@ class Zip243(Zip143):
 
         script_code = derive_script_code(txi, pubkeyhash)  # 13b. scriptCode
         write_varint(h_preimage, len(script_code))
-        write_bytes(h_preimage, script_code)
+        write_bytes_unchecked(h_preimage, script_code)
 
         write_uint64(h_preimage, txi.amount)  # 13c. value
 

core/tests/test_apps.wallet.address.py

@@ -71,7 +71,7 @@ class TestAddress(unittest.TestCase):
         # pubkey OP_CHECKSIG
         script = unhexlify('210279be667ef9dcbbac55a06295ce870b07029bfcdb2dce28d959f2815b16f81798ac')
         h = HashWriter(sha256())
-        write_bytes(h, script)
+        write_bytes_unchecked(h, script)
 
         address = address_p2wsh(
             h.get_digest(),