refactor(core/ethereum): rename and move keccak-related helper functions

diff --git a/core/src/apps/ethereum/helpers.py b/core/src/apps/ethereum/helpers.py
index 2b0b6776..c476c4ce 100644
--- a/core/src/apps/ethereum/helpers.py
+++ b/core/src/apps/ethereum/helpers.py
@@ -11,6 +11,7 @@ if TYPE_CHECKING:
 
     from trezor.messages import EthereumFieldType, EthereumTokenInfo
     from trezor.ui.layouts import StrPropertyType
+    from trezor.utils import HashWriter
 
     from .networks import EthereumNetworkInfo
 
@@ -27,21 +28,21 @@ def address_from_bytes(
     Converts address in bytes to a checksummed string as defined
     in https://github.com/ethereum/EIPs/blob/master/EIPS/eip-55.md
     """
-    from trezor.crypto.hashlib import sha3_256
-
     if network.chain_id in RSKIP60_NETWORKS:
         # rskip60 is a different way to calculate checksum
         prefix = str(network.chain_id) + "0x"
     else:
         prefix = ""
 
-    address_hex = hexlify(address_bytes).decode()
-    digest = sha3_256((prefix + address_hex).encode(), keccak=True).digest()
+    address_hex = hexlify(address_bytes)
+    writer = keccak256(prefix.encode())
+    writer.extend(address_hex)
+    digest = writer.get_digest()
 
     def _maybe_upper(i: int) -> str:
         """Uppercase i-th letter only if the corresponding nibble has high bit set."""
         digest_byte = digest[i // 2]
-        hex_letter = address_hex[i]
+        hex_letter = chr(address_hex[i])
         if i % 2 == 0:
             # even letter -> high nibble
             bit = 0x80
@@ -303,3 +304,10 @@ def get_data_confirmer(total_len: int) -> ConfirmDataFn:
                     return
 
     return confirm_fn
+
+
+def keccak256(data: AnyBytes | None = None) -> HashWriter:
+    from trezor.crypto.hashlib import sha3_256
+    from trezor.utils import HashWriter
+
+    return HashWriter(sha3_256(data=data, keccak=True))
diff --git a/core/src/apps/ethereum/sign_message.py b/core/src/apps/ethereum/sign_message.py
index ce7a7949..312a1f12 100644
--- a/core/src/apps/ethereum/sign_message.py
+++ b/core/src/apps/ethereum/sign_message.py
@@ -13,12 +13,9 @@ if TYPE_CHECKING:
 
 
 def message_digest(message: AnyBytes) -> bytes:
-    from trezor.crypto.hashlib import sha3_256
-    from trezor.utils import HashWriter
+    from .helpers import keccak256
 
-    h = HashWriter(sha3_256(keccak=True))
-    signed_message_header = b"\x19Ethereum Signed Message:\n"
-    h.extend(signed_message_header)
+    h = keccak256(b"\x19Ethereum Signed Message:\n")
     h.extend(str(len(message)).encode())
     h.extend(message)
     return h.get_digest()
diff --git a/core/src/apps/ethereum/sign_tx.py b/core/src/apps/ethereum/sign_tx.py
index 22016159..6e4979ef 100644
--- a/core/src/apps/ethereum/sign_tx.py
+++ b/core/src/apps/ethereum/sign_tx.py
@@ -42,13 +42,11 @@ async def sign_tx(
     keychain: Keychain,
     defs: Definitions,
 ) -> EthereumTxRequest:
-    from trezor.crypto.hashlib import sha3_256
     from trezor.ui.layouts import show_continue_in_app
-    from trezor.utils import HashWriter
 
     from apps.common import paths
 
-    from .helpers import format_ethereum_amount, get_fee_items_regular
+    from .helpers import format_ethereum_amount, get_fee_items_regular, keccak256
 
     # local_cache_attribute
     data_length = msg.data_length
@@ -89,7 +87,7 @@ async def sign_tx(
             amount_size_bytes=32,
         )
 
-    sha = HashWriter(sha3_256(keccak=True))
+    sha = keccak256()
     rlp.write_header(sha, _get_digest_length(msg, data_length), rlp.LIST_HEADER_BYTE)
 
     if tx_type is not None:
diff --git a/core/src/apps/ethereum/sign_tx_eip1559.py b/core/src/apps/ethereum/sign_tx_eip1559.py
index abd259dd..252ae9eb 100644
--- a/core/src/apps/ethereum/sign_tx_eip1559.py
+++ b/core/src/apps/ethereum/sign_tx_eip1559.py
@@ -37,13 +37,11 @@ async def sign_tx_eip1559(
 ) -> EthereumTxRequest:
     from trezor import TR, wire
     from trezor.crypto import rlp  # local_cache_global
-    from trezor.crypto.hashlib import sha3_256
     from trezor.ui.layouts import show_continue_in_app
-    from trezor.utils import HashWriter
 
     from apps.common import paths
 
-    from .helpers import format_ethereum_amount, get_fee_items_eip1559
+    from .helpers import format_ethereum_amount, get_fee_items_eip1559, keccak256
     from .sign_tx import (
         check_common_fields,
         confirm_data_and_summary,
@@ -86,7 +84,7 @@ async def sign_tx_eip1559(
             msg.payment_req, slip44_id, keychain, amount_size_bytes=32
         )
 
-    sha = HashWriter(sha3_256(keccak=True))
+    sha = keccak256()
 
     rlp.write(sha, _TX_TYPE)
     rlp.write_header(sha, _get_digest_length(msg, data_length), rlp.LIST_HEADER_BYTE)
diff --git a/core/src/apps/ethereum/sign_typed_data.py b/core/src/apps/ethereum/sign_typed_data.py
index 276c8c3d..7786c94c 100644
--- a/core/src/apps/ethereum/sign_typed_data.py
+++ b/core/src/apps/ethereum/sign_typed_data.py
@@ -4,7 +4,7 @@ from trezor.enums import EthereumDataType
 from trezor.wire import DataError
 from trezor.wire.context import call
 
-from .helpers import get_type_name
+from .helpers import get_type_name, keccak256
 from .keychain import PATTERNS_ADDRESS, with_keychain_from_path
 from .layout import should_show_struct
 
@@ -137,19 +137,9 @@ async def _generate_typed_data_hash(
 
     await confirm_typed_data_final()
 
-    return keccak256(b"\x19\x01" + domain_separator + message_hash)
-
-
-def get_hash_writer() -> HashWriter:
-    from trezor.crypto.hashlib import sha3_256
-    from trezor.utils import HashWriter
-
-    return HashWriter(sha3_256(keccak=True))
-
-
-def keccak256(message: AnyBytes) -> bytes:
-    h = get_hash_writer()
-    h.extend(message)
+    h = keccak256(b"\x19\x01")
+    h.extend(domain_separator)
+    h.extend(message_hash)
     return h.get_digest()
 
 
@@ -215,7 +205,7 @@ class TypedDataEnvelope:
         report_progress: Callable[[float], None] | None = None,
     ) -> bytes:
         """Generate a hash representation of the whole struct."""
-        w = get_hash_writer()
+        w = keccak256()
         self.hash_type(w, primary_type)
         await self.get_and_encode_data(
             w,
@@ -229,8 +219,7 @@ class TypedDataEnvelope:
 
     def hash_type(self, w: HashWriter, primary_type: str) -> None:
         """Create a representation of a type."""
-        result = keccak256(self.encode_type(primary_type))
-        w.extend(result)
+        w.extend(keccak256(self.encode_type(primary_type)).get_digest())
 
     def encode_type(self, primary_type: str) -> bytes:
         """
@@ -348,7 +337,7 @@ class TypedDataEnvelope:
                 else:
                     show_array = False
 
-                arr_w = get_hash_writer()
+                arr_w = keccak256()
                 el_member_path = member_value_path + [0]
                 for i in range(array_size):
                     el_member_path[-1] = i
@@ -435,7 +424,7 @@ def encode_field(
 
     if data_type == EDT.BYTES:
         if field.size is None:
-            w.extend(keccak256(value))
+            w.extend(keccak256(value).get_digest())
         else:
             # write_rightpad32
             assert len(value) <= 32
@@ -443,7 +432,7 @@ def encode_field(
             for _ in range(32 - len(value)):
                 w.append(0x00)
     elif data_type == EDT.STRING:
-        w.extend(keccak256(value))
+        w.extend(keccak256(value).get_digest())
     elif data_type == EDT.INT:
         write_leftpad32(w, value, signed=True)
     elif data_type in (
diff --git a/core/src/apps/ethereum/verify_message.py b/core/src/apps/ethereum/verify_message.py
index 227e45bf..6f9bdc4a 100644
--- a/core/src/apps/ethereum/verify_message.py
+++ b/core/src/apps/ethereum/verify_message.py
@@ -7,14 +7,13 @@ if TYPE_CHECKING:
 async def verify_message(msg: EthereumVerifyMessage) -> Success:
     from trezor import TR
     from trezor.crypto.curve import secp256k1
-    from trezor.crypto.hashlib import sha3_256
     from trezor.messages import Success
     from trezor.ui.layouts import confirm_signverify, show_success
     from trezor.wire import DataError
 
     from apps.common.signverify import decode_message
 
-    from .helpers import address_from_bytes, bytes_from_address
+    from .helpers import address_from_bytes, bytes_from_address, keccak256
     from .sign_message import message_digest
 
     digest = message_digest(msg.message)
@@ -27,7 +26,7 @@ async def verify_message(msg: EthereumVerifyMessage) -> Success:
     if not pubkey:
         raise DataError("Invalid signature")
 
-    pkh = sha3_256(pubkey[1:], keccak=True).digest()[-20:]
+    pkh = keccak256(pubkey[1:]).get_digest()[-20:]
 
     address_bytes = bytes_from_address(msg.address)
     if address_bytes != pkh:
diff --git a/core/tests/test_apps.ethereum.sign_typed_data.py b/core/tests/test_apps.ethereum.sign_typed_data.py
index f992028c..cde9763c 100644
--- a/core/tests/test_apps.ethereum.sign_typed_data.py
+++ b/core/tests/test_apps.ethereum.sign_typed_data.py
@@ -441,14 +441,14 @@ class TestEthereumSignTypedData(unittest.TestCase):
                 "EIP712Domain",
                 keccak256(
                     b"EIP712Domain(string name,string version,uint256 chainId,address verifyingContract)"
-                ),
+                ).get_digest(),
             ),
-            ("Person", keccak256(b"Person(string name,address wallet)")),
+            ("Person", keccak256(b"Person(string name,address wallet)").get_digest()),
             (
                 "Mail",
                 keccak256(
                     b"Mail(Person from,Person to,string contents)Person(string name,address wallet)"
-                ),
+                ).get_digest(),
             ),
         )
 
@@ -497,12 +497,12 @@ class TestEthereumSignTypedData(unittest.TestCase):
             (
                 EFT(data_type=EDT.STRING, size=None),
                 b"Ether Mail",
-                keccak256(b"Ether Mail"),
+                keccak256(b"Ether Mail").get_digest(),
             ),
             (
                 EFT(data_type=EDT.STRING, size=None),
                 b"1",
-                keccak256(b"1"),
+                keccak256(b"1").get_digest(),
             ),
             (
                 EFT(data_type=EDT.UINT, size=32),