diff --git a/core/src/apps/base.py b/core/src/apps/base.py
index 16b8ee966..e3b73efa3 100644
--- a/core/src/apps/base.py
+++ b/core/src/apps/base.py
@@ -145,6 +145,7 @@ async def handle_DoPreauthorized(
 
     req = await ctx.call_any(PreauthorizedRequest(), *wire_types)
 
+    assert req.MESSAGE_WIRE_TYPE is not None
     handler = workflow_handlers.find_registered_handler(
         ctx.iface, req.MESSAGE_WIRE_TYPE
     )
diff --git a/core/src/apps/common/authorization.py b/core/src/apps/common/authorization.py
index 4a5fc7502..156f821b2 100644
--- a/core/src/apps/common/authorization.py
+++ b/core/src/apps/common/authorization.py
@@ -1,7 +1,8 @@
 import protobuf
 import storage.cache
-from trezor import messages, utils
-from trezor.messages import MessageType
+from trezor import protobuf
+from trezor.enums import MessageType
+from trezor.utils import ensure
 
 if False:
     from typing import Iterable
@@ -16,9 +17,12 @@ def is_set() -> bool:
 
 
 def set(auth_message: protobuf.MessageType) -> None:
-    buffer = bytearray(protobuf.count_message(auth_message))
-    writer = utils.BufferWriter(buffer)
-    protobuf.dump_message(writer, auth_message)
+    buffer = protobuf.dump_message_buffer(auth_message)
+
+    # only wire-level messages can be stored as authorization
+    # (because only wire-level messages have wire_type, which we use as identifier)
+    ensure(auth_message.MESSAGE_WIRE_TYPE is not None)
+    assert auth_message.MESSAGE_WIRE_TYPE is not None  # so that mypy knows as well
     storage.cache.set(
         storage.cache.APP_COMMON_AUTHORIZATION_TYPE,
         auth_message.MESSAGE_WIRE_TYPE.to_bytes(2, "big"),
@@ -32,11 +36,8 @@ def get() -> protobuf.MessageType | None:
         return None
 
     msg_wire_type = int.from_bytes(stored_auth_type, "big")
-    msg_type = messages.get_type(msg_wire_type)
     buffer = storage.cache.get(storage.cache.APP_COMMON_AUTHORIZATION_DATA)
-    reader = utils.BufferReader(buffer)
-
-    return protobuf.load_message(reader, msg_type)
+    return protobuf.load_message_buffer(buffer, msg_wire_type)
 
 
 def get_wire_types() -> Iterable[int]:
diff --git a/core/src/apps/monero/get_tx_keys.py b/core/src/apps/monero/get_tx_keys.py
index 3c960fd2b..748fdebc4 100644
--- a/core/src/apps/monero/get_tx_keys.py
+++ b/core/src/apps/monero/get_tx_keys.py
@@ -50,7 +50,7 @@ async def get_tx_keys(ctx, msg: MoneroGetTxKeyRequest, keychain):
     # and then is used to store the derivations if applicable
     plain_buff = chacha_poly.decrypt_pack(tx_enc_key, msg.tx_enc_keys)
     utils.ensure(len(plain_buff) % 32 == 0, "Tx key buffer has invalid size")
-    del msg.tx_enc_keys
+    msg.tx_enc_keys = b""
 
     # If return only derivations do tx_priv * view_pub
     if do_deriv:
diff --git a/core/src/apps/monero/signing/offloading_keys.py b/core/src/apps/monero/signing/offloading_keys.py
index 9b7449844..8fee2a8a4 100644
--- a/core/src/apps/monero/signing/offloading_keys.py
+++ b/core/src/apps/monero/signing/offloading_keys.py
@@ -134,7 +134,7 @@ def gen_hmac_vini(
     used only once and hard to check. I.e., indices in step 2
     are uncheckable, decoy keys in step 9 are just random keys.
     """
-    import protobuf
+    from trezor import protobuf
     from apps.monero.xmr.keccak_hasher import get_keccak_writer
 
     kwriter = get_keccak_writer()
@@ -146,7 +146,7 @@ def gen_hmac_vini(
             src_entr.real_out_additional_tx_keys[src_entr.real_output_in_tx_index]
         ]
 
-    protobuf.dump_message(kwriter, src_entr)
+    kwriter.write(protobuf.dump_message_buffer(src_entr))
     src_entr.outputs = real_outputs
     src_entr.real_out_additional_tx_keys = real_additional
     kwriter.write(vini_bin)
@@ -162,11 +162,11 @@ def gen_hmac_vouti(
     """
     Generates HMAC for (TxDestinationEntry[i] || tx.vout[i])
     """
-    import protobuf
+    from trezor import protobuf
     from apps.monero.xmr.keccak_hasher import get_keccak_writer
 
     kwriter = get_keccak_writer()
-    protobuf.dump_message(kwriter, dst_entr)
+    kwriter.write(protobuf.dump_message_buffer(dst_entr))
     kwriter.write(tx_out_bin)
 
     hmac_key_vouti = hmac_key_txout(key, idx)
@@ -180,11 +180,11 @@ def gen_hmac_tsxdest(
     """
     Generates HMAC for TxDestinationEntry[i]
     """
-    import protobuf
+    from trezor import protobuf
     from apps.monero.xmr.keccak_hasher import get_keccak_writer
 
     kwriter = get_keccak_writer()
-    protobuf.dump_message(kwriter, dst_entr)
+    kwriter.write(protobuf.dump_message_buffer(dst_entr))
 
     hmac_key = hmac_key_txdst(key, idx)
     hmac_tsxdest = crypto.compute_hmac(hmac_key, kwriter.get_digest())
diff --git a/core/src/apps/monero/signing/step_01_init_transaction.py b/core/src/apps/monero/signing/step_01_init_transaction.py
index 4a621c48b..87d0a37c1 100644
--- a/core/src/apps/monero/signing/step_01_init_transaction.py
+++ b/core/src/apps/monero/signing/step_01_init_transaction.py
@@ -116,7 +116,7 @@ async def init_transaction(
     from trezor.messages.MoneroTransactionInitAck import MoneroTransactionInitAck
     from trezor.messages.MoneroTransactionRsigData import MoneroTransactionRsigData
 
-    rsig_data = MoneroTransactionRsigData(offload_type=state.rsig_offload)
+    rsig_data = MoneroTransactionRsigData(offload_type=int(state.rsig_offload))
 
     return MoneroTransactionInitAck(hmacs=hmacs, rsig_data=rsig_data)
 
@@ -273,11 +273,11 @@ def _compute_sec_keys(state: State, tsx_data: MoneroTransactionData):
     """
     Generate master key H( H(TsxData || tx_priv) || rand )
     """
-    import protobuf
+    from trezor import protobuf
     from apps.monero.xmr.keccak_hasher import get_keccak_writer
 
     writer = get_keccak_writer()
-    protobuf.dump_message(writer, tsx_data)
+    writer.write(protobuf.dump_message_buffer(tsx_data))
     writer.write(crypto.encodeint(state.tx_priv))
 
     master_key = crypto.keccak_2hash(
diff --git a/core/src/apps/monero/xmr/serialize/readwriter.py b/core/src/apps/monero/xmr/serialize/readwriter.py
index 54cd8ddaa..67eec2496 100644
--- a/core/src/apps/monero/xmr/serialize/readwriter.py
+++ b/core/src/apps/monero/xmr/serialize/readwriter.py
@@ -62,9 +62,6 @@ class MemoryReaderWriter:
 
         return nread
 
-    async def areadinto(self, buf):
-        return self.readinto(buf)
-
     def write(self, buf):
         nwritten = len(buf)
         nall = len(self.buffer)
@@ -98,9 +95,6 @@ class MemoryReaderWriter:
         self.ndata += nwritten
         return nwritten
 
-    async def awrite(self, buf):
-        return self.write(buf)
-
     def get_buffer(self):
         mv = memoryview(self.buffer)
         return mv[self.offset : self.woffset]
diff --git a/core/src/protobuf.py b/core/src/protobuf.py
deleted file mode 100644
index 5e879b329..000000000
--- a/core/src/protobuf.py
+++ /dev/null
@@ -1,456 +0,0 @@
-"""
-Extremely minimal streaming codec for a subset of protobuf.  Supports uint32,
-bytes, string, embedded message and repeated fields.
-"""
-
-if False:
-    from typing import (
-        Any,
-        Callable,
-        Iterable,
-        TypeVar,
-        Union,
-    )
-    from typing_extensions import Protocol
-
-    class Reader(Protocol):
-        def readinto(self, buf: bytearray) -> int:
-            """
-            Reads `len(buf)` bytes into `buf`, or raises `EOFError`.
-            """
-
-    class Writer(Protocol):
-        def write(self, buf: bytes) -> int:
-            """
-            Writes all bytes from `buf`, or raises `EOFError`.
-            """
-
-    WriteMethod = Callable[[bytes], Any]
-
-
-_UVARINT_BUFFER = bytearray(1)
-
-
-def load_uvarint(reader: Reader) -> int:
-    buffer = _UVARINT_BUFFER
-    result = 0
-    shift = 0
-    byte = 0x80
-    while byte & 0x80:
-        reader.readinto(buffer)
-        byte = buffer[0]
-        result += (byte & 0x7F) << shift
-        shift += 7
-    return result
-
-
-def dump_uvarint(write: WriteMethod, n: int) -> None:
-    if n < 0:
-        raise ValueError("Cannot dump signed value, convert it to unsigned first.")
-    buffer = _UVARINT_BUFFER
-    shifted = 1
-    while shifted:
-        shifted = n >> 7
-        buffer[0] = (n & 0x7F) | (0x80 if shifted else 0x00)
-        write(buffer)
-        n = shifted
-
-
-def count_uvarint(n: int) -> int:
-    if n < 0:
-        raise ValueError("Cannot dump signed value, convert it to unsigned first.")
-    if n <= 0x7F:
-        return 1
-    if n <= 0x3FFF:
-        return 2
-    if n <= 0x1F_FFFF:
-        return 3
-    if n <= 0xFFF_FFFF:
-        return 4
-    if n <= 0x7_FFFF_FFFF:
-        return 5
-    if n <= 0x3FF_FFFF_FFFF:
-        return 6
-    if n <= 0x1_FFFF_FFFF_FFFF:
-        return 7
-    if n <= 0xFF_FFFF_FFFF_FFFF:
-        return 8
-    if n <= 0x7FFF_FFFF_FFFF_FFFF:
-        return 9
-    raise ValueError
-
-
-# protobuf interleaved signed encoding:
-# https://developers.google.com/protocol-buffers/docs/encoding#structure
-# the idea is to save the sign in LSbit instead of twos-complement.
-# so counting up, you go: 0, -1, 1, -2, 2, ... (as the first bit changes, sign flips)
-#
-# To achieve this with a twos-complement number:
-# 1. shift left by 1, leaving LSbit free
-# 2. if the number is negative, do bitwise negation.
-#    This keeps positive number the same, and converts negative from twos-complement
-#    to the appropriate value, while setting the sign bit.
-#
-# The original algorithm makes use of the fact that arithmetic (signed) shift
-# keeps the sign bits, so for a n-bit number, (x >> n) gets us "all sign bits".
-# Then you can take "number XOR all-sign-bits", which is XOR 0 (identity) for positive
-# and XOR 1 (bitwise negation) for negative. Cute and efficient.
-#
-# But this is harder in Python because we don't natively know the bit size of the number.
-# So we have to branch on whether the number is negative.
-
-
-def sint_to_uint(sint: int) -> int:
-    res = sint << 1
-    if sint < 0:
-        res = ~res
-    return res
-
-
-def uint_to_sint(uint: int) -> int:
-    sign = uint & 1
-    res = uint >> 1
-    if sign:
-        res = ~res
-    return res
-
-
-class UVarintType:
-    WIRE_TYPE = 0
-
-
-class SVarintType:
-    WIRE_TYPE = 0
-
-
-class BoolType:
-    WIRE_TYPE = 0
-
-
-class EnumType:
-    WIRE_TYPE = 0
-
-    def __init__(self, name: str, enum_values: Iterable[int]) -> None:
-        self.enum_values = enum_values
-
-    def validate(self, fvalue: int) -> int:
-        if fvalue in self.enum_values:
-            return fvalue
-        else:
-            raise TypeError("Invalid enum value")
-
-
-class BytesType:
-    WIRE_TYPE = 2
-
-
-class UnicodeType:
-    WIRE_TYPE = 2
-
-
-if False:
-    MessageTypeDef = Union[
-        type[UVarintType],
-        type[SVarintType],
-        type[BoolType],
-        EnumType,
-        type[BytesType],
-        type[UnicodeType],
-        type["MessageType"],
-    ]
-    FieldDef = tuple[str, MessageTypeDef, Any]
-    FieldDict = dict[int, FieldDef]
-
-    FieldCache = dict[type["MessageType"], FieldDict]
-
-    LoadedMessageType = TypeVar("LoadedMessageType", bound="MessageType")
-
-
-class MessageType:
-    WIRE_TYPE = 2
-    UNSTABLE = False
-
-    # Type id for the wire codec.
-    # Technically, not every protobuf message has this.
-    MESSAGE_WIRE_TYPE = -1
-
-    @classmethod
-    def get_fields(cls) -> FieldDict:
-        return {}
-
-    @classmethod
-    def cache_subordinate_types(cls, field_cache: FieldCache) -> None:
-        if cls in field_cache:
-            fields = field_cache[cls]
-        else:
-            fields = cls.get_fields()
-            field_cache[cls] = fields
-
-        for _, field_type, _ in fields.values():
-            if isinstance(field_type, MessageType):
-                field_type.cache_subordinate_types(field_cache)
-
-    def __eq__(self, rhs: Any) -> bool:
-        return self.__class__ is rhs.__class__ and self.__dict__ == rhs.__dict__
-
-    def __repr__(self) -> str:
-        return "<%s>" % self.__class__.__name__
-
-
-class LimitedReader:
-    def __init__(self, reader: Reader, limit: int) -> None:
-        self.reader = reader
-        self.limit = limit
-
-    def readinto(self, buf: bytearray) -> int:
-        if self.limit < len(buf):
-            raise EOFError
-        else:
-            nread = self.reader.readinto(buf)
-            self.limit -= nread
-            return nread
-
-
-FLAG_REPEATED = object()
-FLAG_REQUIRED = object()
-FLAG_EXPERIMENTAL = object()
-
-
-def load_message(
-    reader: Reader,
-    msg_type: type[LoadedMessageType],
-    field_cache: FieldCache | None = None,
-    experimental_enabled: bool = True,
-) -> LoadedMessageType:
-    if field_cache is None:
-        field_cache = {}
-    fields = field_cache.get(msg_type)
-    if fields is None:
-        fields = msg_type.get_fields()
-        field_cache[msg_type] = fields
-
-    if msg_type.UNSTABLE and not experimental_enabled:
-        raise ValueError  # experimental messages not enabled
-
-    # we need to avoid calling __init__, which enforces required arguments
-    msg: LoadedMessageType = object.__new__(msg_type)
-    # pre-seed the object with defaults
-    for fname, _, fdefault in fields.values():
-        if fdefault is FLAG_REPEATED:
-            fdefault = []
-        elif fdefault is FLAG_EXPERIMENTAL:
-            fdefault = None
-        setattr(msg, fname, fdefault)
-
-    if False:
-        SingularValue = Union[int, bool, bytearray, str, MessageType]
-        Value = Union[SingularValue, list[SingularValue]]
-        fvalue: Value = 0
-
-    while True:
-        try:
-            fkey = load_uvarint(reader)
-        except EOFError:
-            break  # no more fields to load
-
-        ftag = fkey >> 3
-        wtype = fkey & 7
-
-        field = fields.get(ftag, None)
-
-        if field is None:  # unknown field, skip it
-            if wtype == 0:
-                load_uvarint(reader)
-            elif wtype == 2:
-                ivalue = load_uvarint(reader)
-                reader.readinto(bytearray(ivalue))
-            else:
-                raise ValueError
-            continue
-
-        fname, ftype, fdefault = field
-        if wtype != ftype.WIRE_TYPE:
-            raise TypeError  # parsed wire type differs from the schema
-
-        if fdefault is FLAG_EXPERIMENTAL and not experimental_enabled:
-            raise ValueError  # experimental fields not enabled
-
-        ivalue = load_uvarint(reader)
-
-        if ftype is UVarintType:
-            fvalue = ivalue
-        elif ftype is SVarintType:
-            fvalue = uint_to_sint(ivalue)
-        elif ftype is BoolType:
-            fvalue = bool(ivalue)
-        elif isinstance(ftype, EnumType):
-            fvalue = ftype.validate(ivalue)
-        elif ftype is BytesType:
-            fvalue = bytearray(ivalue)
-            reader.readinto(fvalue)
-        elif ftype is UnicodeType:
-            fvalue = bytearray(ivalue)
-            reader.readinto(fvalue)
-            fvalue = bytes(fvalue).decode()
-        elif issubclass(ftype, MessageType):
-            fvalue = load_message(
-                LimitedReader(reader, ivalue), ftype, field_cache, experimental_enabled
-            )
-        else:
-            raise TypeError  # field type is unknown
-
-        if fdefault is FLAG_REPEATED:
-            getattr(msg, fname).append(fvalue)
-        else:
-            setattr(msg, fname, fvalue)
-
-    for fname, _, _ in fields.values():
-        if getattr(msg, fname) is FLAG_REQUIRED:
-            # The message is intended to be user-facing when decoding from wire,
-            # but not when used internally.
-            raise ValueError("Required field '{}' was not received".format(fname))
-
-    return msg
-
-
-def dump_message(
-    writer: Writer, msg: MessageType, field_cache: FieldCache | None = None
-) -> None:
-    repvalue = [0]
-
-    if field_cache is None:
-        field_cache = {}
-    fields = field_cache.get(type(msg))
-    if fields is None:
-        fields = msg.get_fields()
-        field_cache[type(msg)] = fields
-
-    for ftag in fields:
-        fname, ftype, fdefault = fields[ftag]
-
-        fvalue = getattr(msg, fname, None)
-        if fvalue is None:
-            continue
-
-        fkey = (ftag << 3) | ftype.WIRE_TYPE
-
-        if fdefault is not FLAG_REPEATED:
-            repvalue[0] = fvalue
-            fvalue = repvalue
-
-        for svalue in fvalue:
-            dump_uvarint(writer.write, fkey)
-
-            if ftype is UVarintType:
-                dump_uvarint(writer.write, svalue)
-
-            elif ftype is SVarintType:
-                dump_uvarint(writer.write, sint_to_uint(svalue))
-
-            elif ftype is BoolType:
-                dump_uvarint(writer.write, int(svalue))
-
-            elif isinstance(ftype, EnumType):
-                dump_uvarint(writer.write, svalue)
-
-            elif ftype is BytesType:
-                if isinstance(svalue, list):
-                    dump_uvarint(writer.write, _count_bytes_list(svalue))
-                    for sub_svalue in svalue:
-                        writer.write(sub_svalue)
-                else:
-                    dump_uvarint(writer.write, len(svalue))
-                    writer.write(svalue)
-
-            elif ftype is UnicodeType:
-                svalue = svalue.encode()
-                dump_uvarint(writer.write, len(svalue))
-                writer.write(svalue)
-
-            elif issubclass(ftype, MessageType):
-                ffields = field_cache.get(ftype)
-                if ffields is None:
-                    ffields = ftype.get_fields()
-                    field_cache[ftype] = ffields
-                dump_uvarint(writer.write, count_message(svalue, field_cache))
-                dump_message(writer, svalue, field_cache)
-
-            else:
-                raise TypeError
-
-
-def count_message(msg: MessageType, field_cache: FieldCache | None = None) -> int:
-    nbytes = 0
-    repvalue = [0]
-
-    if field_cache is None:
-        field_cache = {}
-    fields = field_cache.get(type(msg))
-    if fields is None:
-        fields = msg.get_fields()
-        field_cache[type(msg)] = fields
-
-    for ftag in fields:
-        fname, ftype, fdefault = fields[ftag]
-
-        fvalue = getattr(msg, fname, None)
-        if fvalue is None:
-            continue
-
-        fkey = (ftag << 3) | ftype.WIRE_TYPE
-
-        if fdefault is not FLAG_REPEATED:
-            repvalue[0] = fvalue
-            fvalue = repvalue
-
-        # length of all the field keys
-        nbytes += count_uvarint(fkey) * len(fvalue)
-
-        if ftype is UVarintType:
-            for svalue in fvalue:
-                nbytes += count_uvarint(svalue)
-
-        elif ftype is SVarintType:
-            for svalue in fvalue:
-                nbytes += count_uvarint(sint_to_uint(svalue))
-
-        elif ftype is BoolType:
-            for svalue in fvalue:
-                nbytes += count_uvarint(int(svalue))
-
-        elif isinstance(ftype, EnumType):
-            for svalue in fvalue:
-                nbytes += count_uvarint(svalue)
-
-        elif ftype is BytesType:
-            for svalue in fvalue:
-                if isinstance(svalue, list):
-                    svalue = _count_bytes_list(svalue)
-                else:
-                    svalue = len(svalue)
-                nbytes += count_uvarint(svalue)
-                nbytes += svalue
-
-        elif ftype is UnicodeType:
-            for svalue in fvalue:
-                svalue = len(svalue.encode())
-                nbytes += count_uvarint(svalue)
-                nbytes += svalue
-
-        elif issubclass(ftype, MessageType):
-            for svalue in fvalue:
-                fsize = count_message(svalue, field_cache)
-                nbytes += count_uvarint(fsize)
-                nbytes += fsize
-
-        else:
-            raise TypeError
-
-    return nbytes
-
-
-def _count_bytes_list(svalue: list[bytes]) -> int:
-    res = 0
-    for x in svalue:
-        res += len(x)
-    return res
diff --git a/core/src/trezor/protobuf.py b/core/src/trezor/protobuf.py
new file mode 100644
index 000000000..6fc9b82b9
--- /dev/null
+++ b/core/src/trezor/protobuf.py
@@ -0,0 +1,42 @@
+import trezorproto
+
+decode = trezorproto.decode
+encode = trezorproto.encode
+encoded_length = trezorproto.encoded_length
+type_for_name = trezorproto.type_for_name
+type_for_wire = trezorproto.type_for_wire
+
+# XXX
+# Note that MessageType "subclasses" are not true subclasses, but instead instances
+# of the built-in metaclass MsgDef. MessageType instances are in fact instances of
+# the built-in type Msg. That is why isinstance checks do not work, and instead the
+# MessageTypeSubclass.is_type_of() method must be used.
+if False:
+    from typing import Type, TypeGuard, TypeVar
+
+    T = TypeVar("T", bound="MessageType")
+
+    class MsgDef(type):
+        @classmethod
+        def is_type_of(cls: Type[Type[T]], msg: "MessageType") -> TypeGuard[T]:
+            """Identify if the provided message belongs to this type."""
+            raise NotImplementedError
+
+    class MessageType(metaclass=MsgDef):
+        MESSAGE_NAME: str = "MessageType"
+        MESSAGE_WIRE_TYPE: int | None = None
+
+
+def load_message_buffer(
+    buffer: bytes,
+    msg_wire_type: int,
+    experimental_enabled: bool = True,
+) -> MessageType:
+    msg_type = type_for_wire(msg_wire_type)
+    return decode(buffer, msg_type, experimental_enabled)
+
+
+def dump_message_buffer(msg: MessageType) -> bytearray:
+    buffer = bytearray(encoded_length(msg))
+    encode(buffer, msg)
+    return buffer
diff --git a/core/src/trezor/utils.py b/core/src/trezor/utils.py
index 26039f6ba..2f2852359 100644
--- a/core/src/trezor/utils.py
+++ b/core/src/trezor/utils.py
@@ -145,10 +145,6 @@ class HashWriter:
     def write(self, buf: bytes) -> None:  # alias for extend()
         self.ctx.update(buf)
 
-    async def awrite(self, buf: bytes) -> int:  # AsyncWriter interface
-        self.ctx.update(buf)
-        return len(buf)
-
     def get_digest(self) -> bytes:
         return self.ctx.digest()
 
diff --git a/core/src/trezor/wire/__init__.py b/core/src/trezor/wire/__init__.py
index 040ff5095..ca67810cd 100644
--- a/core/src/trezor/wire/__init__.py
+++ b/core/src/trezor/wire/__init__.py
@@ -35,11 +35,10 @@ reads the message's header. When the message type is known the first handler is
 
 """
 
-import protobuf
 from storage.cache import InvalidSessionError
-from trezor import log, loop, messages, utils, workflow
-from trezor.messages import FailureType
-from trezor.messages.Failure import Failure
+from trezor.enums import FailureType
+from trezor.messages import Failure
+from trezor import log, loop, protobuf, utils, workflow
 from trezor.wire import codec_v1
 from trezor.wire.errors import ActionCancelled, DataError, Error
 
@@ -74,17 +73,19 @@ def setup(iface: WireInterface, is_debug_session: bool = False) -> None:
 
 
 if False:
-    from typing import Protocol
+    from typing import Protocol, TypeVar
+
+    LoadedMessageType = TypeVar("LoadedMessageType", bound=protobuf.MessageType)
 
     class GenericContext(Protocol):
         async def call(
             self,
             msg: protobuf.MessageType,
-            expected_type: type[protobuf.LoadedMessageType],
+            expected_type: type[protobuf.MessageType],
         ) -> Any:
             ...
 
-        async def read(self, expected_type: type[protobuf.LoadedMessageType]) -> Any:
+        async def read(self, expected_type: type[protobuf.MessageType]) -> Any:
             ...
 
         async def write(self, msg: protobuf.MessageType) -> None:
@@ -96,15 +97,14 @@ if False:
 
 
 def _wrap_protobuf_load(
-    reader: protobuf.Reader,
-    expected_type: type[protobuf.LoadedMessageType],
-    field_cache: protobuf.FieldCache | None = None,
-) -> protobuf.LoadedMessageType:
+    buffer: bytes,
+    expected_type: type[LoadedMessageType],
+) -> LoadedMessageType:
     try:
-        return protobuf.load_message(
-            reader, expected_type, field_cache, experimental_enabled
-        )
+        return protobuf.decode(buffer, expected_type, experimental_enabled)
     except Exception as e:
+        if __debug__:
+            log.exception(__name__, e)
         if e.args:
             raise DataError("Failed to decode message: {}".format(e.args[0]))
         else:
@@ -139,19 +139,15 @@ class Context:
         self.iface = iface
         self.sid = sid
         self.buffer = buffer
-        self.buffer_writer = utils.BufferWriter(self.buffer)
-
-        self._field_cache: protobuf.FieldCache = {}
 
     async def call(
         self,
         msg: protobuf.MessageType,
-        expected_type: type[protobuf.LoadedMessageType],
-        field_cache: protobuf.FieldCache | None = None,
-    ) -> protobuf.LoadedMessageType:
-        await self.write(msg, field_cache)
+        expected_type: type[LoadedMessageType],
+    ) -> LoadedMessageType:
+        await self.write(msg)
         del msg
-        return await self.read(expected_type, field_cache)
+        return await self.read(expected_type)
 
     async def call_any(
         self, msg: protobuf.MessageType, *expected_wire_types: int
@@ -160,21 +156,17 @@ class Context:
         del msg
         return await self.read_any(expected_wire_types)
 
-    async def read_from_wire(self) -> codec_v1.Message:
-        return await codec_v1.read_message(self.iface, self.buffer)
+    def read_from_wire(self) -> Awaitable[codec_v1.Message]:
+        return codec_v1.read_message(self.iface, self.buffer)
 
-    async def read(
-        self,
-        expected_type: type[protobuf.LoadedMessageType],
-        field_cache: protobuf.FieldCache | None = None,
-    ) -> protobuf.LoadedMessageType:
+    async def read(self, expected_type: type[LoadedMessageType]) -> LoadedMessageType:
         if __debug__:
             log.debug(
                 __name__,
                 "%s:%x expect: %s",
                 self.iface.iface_num(),
                 self.sid,
-                expected_type,
+                expected_type.MESSAGE_NAME,
             )
 
         # Load the full message into a buffer, parse out type and data payload
@@ -191,13 +183,13 @@ class Context:
                 "%s:%x read: %s",
                 self.iface.iface_num(),
                 self.sid,
-                expected_type,
+                expected_type.MESSAGE_NAME,
             )
 
         workflow.idle_timer.touch()
 
         # look up the protobuf class and parse the message
-        return _wrap_protobuf_load(msg.data, expected_type, field_cache)
+        return _wrap_protobuf_load(msg.data, expected_type)
 
     async def read_any(
         self, expected_wire_types: Iterable[int]
@@ -220,11 +212,15 @@ class Context:
             raise UnexpectedMessageError(msg)
 
         # find the protobuf type
-        exptype = messages.get_type(msg.type)
+        exptype = protobuf.type_for_wire(msg.type)
 
         if __debug__:
             log.debug(
-                __name__, "%s:%x read: %s", self.iface.iface_num(), self.sid, exptype
+                __name__,
+                "%s:%x read: %s",
+                self.iface.iface_num(),
+                self.sid,
+                exptype.MESSAGE_NAME,
             )
 
         workflow.idle_timer.touch()
@@ -232,41 +228,36 @@ class Context:
         # parse the message and return it
         return _wrap_protobuf_load(msg.data, exptype)
 
-    async def write(
-        self,
-        msg: protobuf.MessageType,
-        field_cache: protobuf.FieldCache | None = None,
-    ) -> None:
+    async def write(self, msg: protobuf.MessageType) -> None:
         if __debug__:
             log.debug(
-                __name__, "%s:%x write: %s", self.iface.iface_num(), self.sid, msg
+                __name__,
+                "%s:%x write: %s",
+                self.iface.iface_num(),
+                self.sid,
+                msg.MESSAGE_NAME,
             )
 
-        if field_cache is None:
-            field_cache = self._field_cache
+        # cannot write message without wire type
+        assert msg.MESSAGE_WIRE_TYPE is not None
 
-        # write the message
-        msg_size = protobuf.count_message(msg, field_cache)
+        msg_size = protobuf.encoded_length(msg)
 
-        # prepare buffer
-        if msg_size <= len(self.buffer_writer.buffer):
+        if msg_size <= len(self.buffer):
             # reuse preallocated
-            buffer_writer = self.buffer_writer
+            buffer = self.buffer
         else:
             # message is too big, we need to allocate a new buffer
-            buffer_writer = utils.BufferWriter(bytearray(msg_size))
+            buffer = bytearray(msg_size)
+
+        msg_size = protobuf.encode(buffer, msg)
 
-        buffer_writer.seek(0)
-        protobuf.dump_message(buffer_writer, msg, field_cache)
         await codec_v1.write_message(
             self.iface,
             msg.MESSAGE_WIRE_TYPE,
-            memoryview(buffer_writer.buffer)[:msg_size],
+            memoryview(buffer)[:msg_size],
         )
 
-        # make sure we don't keep around fields of all protobuf types ever
-        self._field_cache.clear()
-
     def wait(self, *tasks: Awaitable) -> Any:
         """
         Wait until one of the passed tasks finishes, and return the result,
@@ -301,8 +292,8 @@ async def _handle_single_message(
     """
     if __debug__:
         try:
-            msg_type = messages.get_type(msg.type).__name__
-        except KeyError:
+            msg_type = protobuf.type_for_wire(msg.type).MESSAGE_NAME
+        except Exception:
             msg_type = "%d - unknown message type" % msg.type
         log.debug(
             __name__,
@@ -328,7 +319,7 @@ async def _handle_single_message(
     try:
         # Find a protobuf.MessageType subclass that describes this
         # message.  Raises if the type is not found.
-        req_type = messages.get_type(msg.type)
+        req_type = protobuf.type_for_wire(msg.type)
 
         # Try to decode the message according to schema from
         # `req_type`. Raises if the message is malformed.
@@ -424,6 +415,11 @@ async def handle_session(
                 next_msg = await _handle_single_message(
                     ctx, msg, use_workflow=not is_debug_session
                 )
+            except Exception as exc:
+                # Log and ignore. The session handler can only exit explicitly in the
+                # following finally block.
+                if __debug__:
+                    log.exception(__name__, exc)
             finally:
                 if not __debug__ or not is_debug_session:
                     # Unload modules imported by the workflow.  Should not raise.
diff --git a/core/src/trezor/wire/codec_v1.py b/core/src/trezor/wire/codec_v1.py
index 67c89c070..153704aa2 100644
--- a/core/src/trezor/wire/codec_v1.py
+++ b/core/src/trezor/wire/codec_v1.py
@@ -23,7 +23,7 @@ class CodecError(Exception):
 
 
 class Message:
-    def __init__(self, mtype: int, mdata: utils.BufferReader) -> None:
+    def __init__(self, mtype: int, mdata: bytes) -> None:
         self.type = mtype
         self.data = mdata
 
@@ -70,7 +70,7 @@ async def read_message(iface: WireInterface, buffer: utils.BufferType) -> Messag
     if read_and_throw_away:
         raise CodecError("Message too large")
 
-    return Message(mtype, utils.BufferReader(mdata))
+    return Message(mtype, mdata)
 
 
 async def write_message(iface: WireInterface, mtype: int, mdata: bytes) -> None:
diff --git a/core/tests/test_protobuf.py b/core/tests/test_protobuf.py
deleted file mode 100644
index 31b69c881..000000000
--- a/core/tests/test_protobuf.py
+++ /dev/null
@@ -1,129 +0,0 @@
-from common import *
-
-import protobuf
-from trezor.utils import BufferReader, BufferWriter
-
-
-class Message(protobuf.MessageType):
-    def __init__(self, sint_field: int = 0, enum_field: int = 0) -> None:
-        self.sint_field = sint_field
-        self.enum_field = enum_field
-
-    @classmethod
-    def get_fields(cls):
-        return {
-            1: ("sint_field", protobuf.SVarintType, 0),
-            2: ("enum_field", protobuf.EnumType("t", (0, 5, 25)), 0),
-        }
-
-
-class MessageWithRequiredAndDefault(protobuf.MessageType):
-    def __init__(self, required_field, default_field) -> None:
-        self.required_field = required_field
-        self.default_field = default_field
-
-    @classmethod
-    def get_fields(cls):
-        return {
-            1: ("required_field", protobuf.UVarintType, protobuf.FLAG_REQUIRED),
-            2: ("default_field", protobuf.SVarintType, -1),
-        }
-
-
-def load_uvarint(data: bytes) -> int:
-    reader = BufferReader(data)
-    return protobuf.load_uvarint(reader)
-
-
-def dump_uvarint(value: int) -> bytearray:
-    w = bytearray()
-    protobuf.dump_uvarint(w.extend, value)
-    return w
-
-
-def dump_message(msg: protobuf.MessageType) -> bytearray:
-    length = protobuf.count_message(msg)
-    buffer = bytearray(length)
-    protobuf.dump_message(BufferWriter(buffer), msg)
-    return buffer
-
-
-def load_message(msg_type, buffer: bytearray) -> protobuf.MessageType:
-    return protobuf.load_message(BufferReader(buffer), msg_type)
-
-
-class TestProtobuf(unittest.TestCase):
-    def test_dump_uvarint(self):
-        self.assertEqual(dump_uvarint(0), b"\x00")
-        self.assertEqual(dump_uvarint(1), b"\x01")
-        self.assertEqual(dump_uvarint(0xFF), b"\xff\x01")
-        self.assertEqual(dump_uvarint(123456), b"\xc0\xc4\x07")
-        with self.assertRaises(ValueError):
-            dump_uvarint(-1)
-
-    def test_load_uvarint(self):
-        self.assertEqual(load_uvarint(b"\x00"), 0)
-        self.assertEqual(load_uvarint(b"\x01"), 1)
-        self.assertEqual(load_uvarint(b"\xff\x01"), 0xFF)
-        self.assertEqual(load_uvarint(b"\xc0\xc4\x07"), 123456)
-
-    def test_sint_uint(self):
-        self.assertEqual(protobuf.uint_to_sint(0), 0)
-        self.assertEqual(protobuf.sint_to_uint(0), 0)
-
-        self.assertEqual(protobuf.sint_to_uint(-1), 1)
-        self.assertEqual(protobuf.sint_to_uint(1), 2)
-
-        self.assertEqual(protobuf.uint_to_sint(1), -1)
-        self.assertEqual(protobuf.uint_to_sint(2), 1)
-
-        # roundtrip:
-        self.assertEqual(
-            protobuf.uint_to_sint(protobuf.sint_to_uint(1234567891011)), 1234567891011
-        )
-        self.assertEqual(
-            protobuf.uint_to_sint(protobuf.sint_to_uint(-(2 ** 32))), -(2 ** 32)
-        )
-
-    def test_validate_enum(self):
-        # ok message:
-        msg = Message(-42, 5)
-        msg_encoded = dump_message(msg)
-        nmsg = load_message(Message, msg_encoded)
-
-        self.assertEqual(msg.sint_field, nmsg.sint_field)
-        self.assertEqual(msg.enum_field, nmsg.enum_field)
-
-        # bad enum value:
-        msg = Message(-42, 42)
-        msg_encoded = dump_message(msg)
-        with self.assertRaises(TypeError):
-            load_message(Message, msg_encoded)
-
-    def test_required(self):
-        msg = MessageWithRequiredAndDefault(required_field=1, default_field=2)
-        msg_encoded = dump_message(msg)
-        nmsg = load_message(MessageWithRequiredAndDefault, msg_encoded)
-
-        self.assertEqual(nmsg.required_field, 1)
-        self.assertEqual(nmsg.default_field, 2)
-
-        # try a message without the required_field
-        msg = MessageWithRequiredAndDefault(required_field=None, default_field=2)
-        # encoding always succeeds
-        msg_encoded = dump_message(msg)
-        with self.assertRaises(ValueError):
-            load_message(MessageWithRequiredAndDefault, msg_encoded)
-
-        # try a message without the default field
-        msg = MessageWithRequiredAndDefault(required_field=1, default_field=None)
-        msg_encoded = dump_message(msg)
-        nmsg = load_message(MessageWithRequiredAndDefault, msg_encoded)
-
-        self.assertEqual(nmsg.required_field, 1)
-        self.assertEqual(nmsg.default_field, -1)
-
-
-
-if __name__ == "__main__":
-    unittest.main()
diff --git a/core/tests/test_trezor.protobuf.py b/core/tests/test_trezor.protobuf.py
new file mode 100644
index 000000000..4576c5ac5
--- /dev/null
+++ b/core/tests/test_trezor.protobuf.py
@@ -0,0 +1,115 @@
+from common import *
+
+from trezor import protobuf
+from trezor.messages import WebAuthnCredential, EosAsset, Failure, SignMessage
+
+
+def load_uvarint32(data: bytes) -> int:
+    # use known uint32 field in an all-optional message
+    buffer = bytearray(len(data) + 1)
+    buffer[1:] = data
+    buffer[0] = (1 << 3) | 0  # field number 1, wire type 0
+    msg = protobuf.decode(buffer, WebAuthnCredential, False)
+    return msg.index
+
+
+def load_uvarint64(data: bytes) -> int:
+    # use known uint64 field in an all-optional message
+    buffer = bytearray(len(data) + 1)
+    buffer[1:] = data
+    buffer[0] = (2 << 3) | 0  # field number 1, wire type 0
+    msg = protobuf.decode(buffer, EosAsset, False)
+    return msg.symbol
+
+
+def dump_uvarint32(value: int) -> bytearray:
+    # use known uint32 field in an all-optional message
+    msg = WebAuthnCredential(index=value)
+    length = protobuf.encoded_length(msg)
+    buffer = bytearray(length)
+    protobuf.encode(buffer, msg)
+    assert buffer[0] == (1 << 3) | 0  # field number 1, wire type 0
+    return buffer[1:]
+
+
+def dump_uvarint64(value: int) -> bytearray:
+    # use known uint64 field in an all-optional message
+    msg = EosAsset(symbol=value)
+    length = protobuf.encoded_length(msg)
+    buffer = bytearray(length)
+    protobuf.encode(buffer, msg)
+    assert buffer[0] == (2 << 3) | 0  # field number 2, wire type 0
+    return buffer[1:]
+
+
+def dump_message(msg: protobuf.MessageType) -> bytearray:
+    length = protobuf.encoded_length(msg)
+    buffer = bytearray(length)
+    protobuf.encode(buffer, msg)
+    return buffer
+
+
+def load_message(msg_type: Type[protobuf.MessageType], buffer: bytes) -> protobuf.MessageType:
+    return protobuf.decode(buffer, msg_type, False)
+
+
+class TestProtobuf(unittest.TestCase):
+    def test_dump_uvarint(self):
+        for dump_uvarint in (dump_uvarint32, dump_uvarint64):
+            self.assertEqual(dump_uvarint(0), b"\x00")
+            self.assertEqual(dump_uvarint(1), b"\x01")
+            self.assertEqual(dump_uvarint(0xFF), b"\xff\x01")
+            self.assertEqual(dump_uvarint(123456), b"\xc0\xc4\x07")
+            with self.assertRaises(ValueError):
+                dump_uvarint(-1)
+
+    def test_load_uvarint(self):
+        for load_uvarint in (load_uvarint32, load_uvarint64):
+            self.assertEqual(load_uvarint(b"\x00"), 0)
+            self.assertEqual(load_uvarint(b"\x01"), 1)
+            self.assertEqual(load_uvarint(b"\xff\x01"), 0xFF)
+            self.assertEqual(load_uvarint(b"\xc0\xc4\x07"), 123456)
+
+    def test_validate_enum(self):
+        # ok message:
+        msg = Failure(code=7)
+        msg_encoded = dump_message(msg)
+        nmsg = load_message(Failure, msg_encoded)
+
+        self.assertEqual(msg.code, nmsg.code)
+
+        # bad enum value:
+        msg = Failure(code=1000)
+        msg_encoded = dump_message(msg)
+        with self.assertRaises(ValueError):
+            load_message(Failure, msg_encoded)
+
+    def test_required(self):
+        msg = SignMessage(message=b"hello", coin_name="foo", script_type=1)
+        msg_encoded = dump_message(msg)
+        nmsg = load_message(SignMessage, msg_encoded)
+
+        self.assertEqual(nmsg.message, b"hello")
+        self.assertEqual(nmsg.coin_name, "foo")
+        self.assertEqual(nmsg.script_type, 1)
+
+        # try a message without the required_field
+        msg = SignMessage(message=None)
+        # encoding always succeeds
+        msg_encoded = dump_message(msg)
+        with self.assertRaises(ValueError):
+            load_message(SignMessage, msg_encoded)
+
+        # try a message without the default field
+        msg = SignMessage(message=b"hello")
+        msg.coin_name = None
+        msg_encoded = dump_message(msg)
+        nmsg = load_message(SignMessage, msg_encoded)
+
+        self.assertEqual(nmsg.message, b"hello")
+        self.assertEqual(nmsg.coin_name, "Bitcoin")
+
+
+
+if __name__ == "__main__":
+    unittest.main()
diff --git a/core/tests/test_trezor.wire.codec_v1.py b/core/tests/test_trezor.wire.codec_v1.py
index 3e8cab290..1e2939a4b 100644
--- a/core/tests/test_trezor.wire.codec_v1.py
+++ b/core/tests/test_trezor.wire.codec_v1.py
@@ -53,7 +53,7 @@ class TestWireCodecV1(unittest.TestCase):
         # e.value is StopIteration. e.value.value is the return value of the call
         result = e.value.value
         self.assertEqual(result.type, MESSAGE_TYPE)
-        self.assertEqual(result.data.buffer, b"")
+        self.assertEqual(result.data, b"")
 
         # message should have been read into the buffer
         self.assertEqual(buffer, b"\x00" * 64)
@@ -83,7 +83,7 @@ class TestWireCodecV1(unittest.TestCase):
         # e.value is StopIteration. e.value.value is the return value of the call
         result = e.value.value
         self.assertEqual(result.type, MESSAGE_TYPE)
-        self.assertEqual(result.data.buffer, message)
+        self.assertEqual(result.data, message)
 
         # message should have been read into the buffer
         self.assertEqual(buffer, message)
@@ -108,7 +108,7 @@ class TestWireCodecV1(unittest.TestCase):
         # e.value is StopIteration. e.value.value is the return value of the call
         result = e.value.value
         self.assertEqual(result.type, MESSAGE_TYPE)
-        self.assertEqual(result.data.buffer, message)
+        self.assertEqual(result.data, message)
 
         # read should have allocated its own buffer and not touch ours
         self.assertEqual(buffer, b"\x00")
@@ -176,7 +176,7 @@ class TestWireCodecV1(unittest.TestCase):
 
         result = e.value.value
         self.assertEqual(result.type, MESSAGE_TYPE)
-        self.assertEqual(result.data.buffer, message)
+        self.assertEqual(result.data, message)
 
     def test_read_huge_packet(self):
         PACKET_COUNT = 100_000