diff --git a/src/lib/protobuf/protobuf_streaming.py b/src/lib/protobuf/protobuf_streaming.py
new file mode 100644
index 000000000..95e12adc9
--- /dev/null
+++ b/src/lib/protobuf/protobuf_streaming.py
@@ -0,0 +1,266 @@
+'''Streaming protobuf codec.
+
+Handles asynchronous encoding and decoding of protobuf value streams.
+
+Value format: ((field_type, field_flags, field_name), field_value)
+    field_type: Either one of UVarintType, BoolType, BytesType, UnicodeType,
+                or an instance of EmbeddedMessage.
+    field_flags (int): Field bit flags `FLAG_REQUIRED`, `FLAG_REPEATED`.
+    field_name (str): Field name string.
+    field_value: Depends on field_type.  EmbeddedMessage has `field_value == None`.
+'''
+
+
+def build_protobuf_message(message_type, future):
+    message = message_type()
+    try:
+        while True:
+            field, field_value = yield
+            field_type, field_flags, field_name = field
+            if not _is_scalar_type(field_type):
+                field_value = yield from build_protobuf_message(field_type, future)
+            if field_flags & FLAG_REPEATED:
+                field_value = getattr(
+                    message, field_name, []).append(field_value)
+            setattr(message, field_name, field_value)
+    except EOFError:
+        future.resolve(message)
+
+
+def print_protobuf_message(message_type):
+    print('OPEN', message_type)
+    try:
+        while True:
+            field, field_value = yield
+            field_type, _, field_name = field
+            if not _is_scalar_type(field_type):
+                yield from print_protobuf_message(field_type)
+            else:
+                print('FIELD', field_name, field_type, field_value)
+    except EOFError:
+        print('CLOSE', message_type)
+
+
+class UVarintType:
+    WIRE_TYPE = 0
+
+    @staticmethod
+    def dump(target, value):
+        shifted_value = True
+        while shifted_value:
+            shifted_value = value >> 7
+            yield from target.write(chr((value & 0x7F) | (
+                0x80 if shifted_value != 0 else 0x00)))
+            value = shifted_value
+
+    @staticmethod
+    def load(source):
+        value, shift, quantum = 0, 0, 0x80
+        while (quantum & 0x80) == 0x80:
+            data = yield from source.read(1)
+            quantum = ord(data)
+            value, shift = value + ((quantum & 0x7F) << shift), shift + 7
+        return value
+
+
+class BoolType:
+    WIRE_TYPE = 0
+
+    @staticmethod
+    def dump(target, value):
+        yield from target.write('\x01' if value else '\x00')
+
+    @staticmethod
+    def load(source):
+        varint = yield from UVarintType.load(source)
+        return varint != 0
+
+
+class BytesType:
+    WIRE_TYPE = 2
+
+    @staticmethod
+    def dump(target, value):
+        yield from UVarintType.dump(target, len(value))
+        yield from target.write(value)
+
+    @staticmethod
+    def load(source):
+        size = yield from UVarintType.load(source)
+        data = yield from source.read(size)
+        return data
+
+
+class UnicodeType:
+    WIRE_TYPE = 2
+
+    @staticmethod
+    def dump(target, value):
+        yield from BytesType.dump(target, bytes(value, 'utf-8'))
+
+    @staticmethod
+    def load(source):
+        data = yield from BytesType.load(source)
+        return data.decode('utf-8', 'strict')
+
+
+class EmbeddedMessage:
+    WIRE_TYPE = 2
+
+    def __init__(self, message_type):
+        '''Initializes a new instance. The argument is an underlying message type.'''
+        self.message_type = message_type
+
+    def __call__(self):
+        '''Creates a message of the underlying message type.'''
+        return self.message_type()
+
+    def dump(self, target, value):
+        buf = self.message_type.dumps(value)
+        yield from BytesType.dump(target, buf)
+
+    def load(self, source, target):
+        emb_size = yield from UVarintType.load(source)
+        emb_source = source.limit(emb_size)
+        yield from self.message_type.load(emb_source, target)
+
+
+FLAG_SIMPLE = const(0)
+FLAG_REQUIRED = const(1)
+FLAG_REPEATED = const(2)
+
+
+# Packs a tag and a wire_type into single int according to the protobuf spec.
+_pack_key = lambda tag, wire_type: (tag << 3) | wire_type
+# Unpacks a key into a tag and a wire_type according to the protobuf spec.
+_unpack_key = lambda key: (key >> 3, key & 7)
+# Determines if a field type is a scalar or not.
+_is_scalar_type = lambda field_type: not isinstance(
+    field_type, EmbeddedMessage)
+
+
+class AsyncBytearrayWriter:
+
+    def __init__(self):
+        self.buf = bytearray()
+
+    async def write(self, b):
+        self.buf.extend(b)
+
+
+class MessageType:
+    '''Represents a message type.'''
+
+    def __init__(self, name=None):
+        self.__name = name
+        self.__fields = {}  # tag -> tuple of field_type, field_flags, field_name
+        self.__defaults = {}  # tag -> default_value
+
+    def add_field(self, tag, name, field_type, flags=FLAG_SIMPLE, default=None):
+        '''Adds a field to the message type.'''
+        if tag in self.__fields:
+            raise ValueError('The tag %s is already used.' % tag)
+        if default is not None:
+            self.__defaults[tag] = default
+        self.__fields[tag] = (field_type, flags, name)
+
+    def __call__(self, **fields):
+        '''Creates an instance of this message type.'''
+        return Message(self, **fields)
+
+    def dumps(self, value):
+        target = AsyncBytearrayWriter()
+        yield from self.dump(target, value)
+        return target.buf
+
+    def dump(self, target, value):
+        if self is not value.message_type:
+            raise TypeError('Incompatible type')
+        for tag, field in self.__fields.items():
+            field_type, field_flags, field_name = field
+            if field_name not in value.__dict__:
+                if field_flags & FLAG_REQUIRED:
+                    raise ValueError(
+                        'The field with the tag %s is required but a value is missing.' % tag)
+                else:
+                    continue
+            if field_flags & FLAG_REPEATED:
+                # repeated value
+                key = _pack_key(tag, field_type.WIRE_TYPE)
+                # send the values sequentially
+                for single_value in getattr(value, field_name):
+                    yield from UVarintType.dump(target, key)
+                    yield from field_type.dump(target, single_value)
+            else:
+                # single value
+                yield from UVarintType.dump(target, _pack_key(tag, field_type.WIRE_TYPE))
+                yield from field_type.dump(target, getattr(value, field_name))
+
+    def load(self, source, target):
+        found_tags = set()
+
+        try:
+            while True:
+                key = yield from UVarintType.load(source)
+                tag, wire_type = _unpack_key(key)
+                found_tags.add(tag)
+
+                if tag in self.__fields:
+                    # retrieve the field descriptor by tag
+                    field = self.__fields[tag]
+                    field_type, _, _ = field
+                    if wire_type != field_type.WIRE_TYPE:
+                        raise TypeError(
+                            'Value of tag %s has incorrect wiretype %s, %s expected.' %
+                            (tag, wire_type, field_type.WIRE_TYPE))
+                else:
+                    # unknown field, skip it
+                    field_type = {0: UVarintType, 2: BytesType}[wire_type]
+                    yield from field_type.load(source)
+                    continue
+
+                if _is_scalar_type(field_type):
+                    field_value = yield from field_type.load(source)
+                    target.send((field, field_value))
+                else:
+                    yield from field_type.load(source, target)
+
+        except EOFError:
+            for tag, field in self.__fields.items():
+                # send the default value
+                if tag not in found_tags and tag in self.__defaults:
+                    target.send((field, self.__defaults[tag]))
+                    found_tags.add(tag)
+
+                # check if all required fields are present
+                _, field_flags, field_name = field
+                if field_flags & FLAG_REQUIRED and tag not in found_tags:
+                    if field_flags & FLAG_REPEATED:
+                        # no values were in input stream, but required field.
+                        # send empty list
+                        target.send((field, []))
+                    else:
+                        raise ValueError(
+                            'The field %s (\'%s\') is required but missing.' % (tag, field_name))
+            target.throw(EOFError)
+
+    def __repr__(self):
+        return '<MessageType: %s>' % self.__name
+
+
+class Message:
+    '''Represents a message instance.'''
+
+    def __init__(self, message_type, **fields):
+        '''Initializes a new instance of the specified message type.'''
+        self.message_type = message_type
+        for key in fields:
+            setattr(self, key, fields[key])
+
+    def dump(self, target):
+        yield from self.message_type.dump(target, self)
+
+    def __repr__(self):
+        values = self.__dict__
+        values = {k: values[k] for k in values if k != 'message_type'}
+        return '<%s: %s>' % (self.message_type.__name, values)
diff --git a/src/trezor/wire_streaming.py b/src/trezor/wire_streaming.py
new file mode 100644
index 000000000..fd65e12ca
--- /dev/null
+++ b/src/trezor/wire_streaming.py
@@ -0,0 +1,166 @@
+import ustruct
+import ubinascii
+
+from . import msg
+from . import loop
+from .crypto import random
+
+
+MESSAGE_IFACE = const(0)
+EMPTY_SESSION = const(0)
+
+sessions = {}
+
+
+def generate_session_id():
+    return random.uniform(0xffffffff) + 1
+
+
+async def dispatch_reports():
+    while True:
+        report = await _read_report()
+        session_id, report_data = _parse_report(report)
+        sessions[session_id].send(report_data)
+
+
+async def read_session_message(session_id, types):
+    future = loop.Future()
+    pbuf_decoder = _decode_protobuf_message(types, future)
+    wire_decoder = _decode_wire_message(pbuf_decoder)
+    assert session_id not in sessions
+    sessions[session_id] = wire_decoder
+    try:
+        result = await future
+    finally:
+        del sessions[session_id]
+    return result
+
+
+def lookup_protobuf_type(msg_type, pbuf_types):
+    for pt in pbuf_types:
+        if pt.wire_type == msg_type:
+            return pt
+    return None
+
+
+def _decode_protobuf_message(types, future):
+    msg_type, _ = yield
+    pbuf_type = lookup_protobuf_type(msg_type, types)
+    target = build_protobuf_message(pbuf_type, future)
+    yield from pbuf_type.load(AsyncBytearrayReader(), target)
+
+
+class AsyncBytearrayReader:
+
+    def __init__(self, buf=None, n=None):
+        self.buf = buf if buf is not None else bytearray()
+        self.n = n
+
+    def read(self, n):
+        if self.n is not None:
+            self.n -= n
+            if self.n <= 0:
+                raise EOFError()
+        buf = self.buf
+        while len(buf) < n:
+            buf.extend((yield))  # buffer next data chunk
+        result, buf[:] = buf[:n], buf[n:]
+        return result
+
+    def limit(self, n):
+        return AsyncBytearrayReader(self.buf, n)
+
+
+async def _read_report():
+    report, = await loop.Select(MESSAGE_IFACE)
+    return memoryview(report)  # make slicing cheap
+
+
+async def _write_report(report):
+    return msg.send(MESSAGE_IFACE, report)
+
+
+# TREZOR wire protocol v2:
+#
+# HID report (64B):
+# - report magic (1B)
+# - session (4B, BE)
+# - payload (59B)
+#
+# message:
+# - streamed as payloads of HID reports:
+# - message type (4B, BE)
+# - data length (4B, BE)
+# - data (var-length)
+# - data checksum (4B, BE)
+
+
+REP_HEADER = '>BL'  # marker, session id
+MSG_HEADER = '>LL'  # msg type, data length
+MSG_FOOTER = '>L'  # data checksum
+
+REP_HEADER_LEN = ustruct.calcsize(REP_HEADER)
+MSG_HEADER_LEN = ustruct.calcsize(MSG_HEADER)
+MSG_FOOTER_LEN = ustruct.calcsize(MSG_FOOTER)
+
+
+class MessageChecksumError(Exception):
+    pass
+
+
+def _parse_report(data):
+    marker, session_id = ustruct.parse(REP_HEADER, data)
+    return session_id, data[REP_HEADER_LEN:]
+
+
+def _parse_message(data):
+    msg_type, data_len = ustruct.parse(MSG_HEADER, data)
+    return msg_type, data_len, data[MSG_HEADER_LEN:]
+
+
+def _parse_footer(data):
+    data_checksum, = ustruct.parse(MSG_FOOTER, data)
+    return data_checksum,
+
+
+def _decode_wire_message(target):
+    '''Decode a wire message from the report data and stream it to target.
+
+Receives report payloads.
+Sends (msg_type, data_len) to target, followed by data chunks.
+Throws EOFError after last data chunk, in case of valid checksum.
+Throws MessageChecksumError to target if data doesn't match the checksum.
+'''
+    message = (yield)  # read first report
+    msg_type, data_len, data_tail = _parse_message(message)
+    target.send((msg_type, data_len))
+
+    checksum = 0  # crc32
+    nreports = 1
+
+    while data_len > 0:
+        if nreports > 1:
+            data_tail = (yield)  # read next report
+        nreports += 1
+
+        data_chunk = data_tail[:data_len]  # slice off the garbage at the end
+        data_tail = data_tail[len(data_chunk):]  # slice off what we have read
+        data_len -= len(data_chunk)
+        target.send(data_chunk)
+
+        checksum = ubinascii.crc32(checksum, data_chunk)
+
+    data_footer = data_tail[:MSG_FOOTER_LEN]
+    if len(data_footer) < MSG_FOOTER_LEN:
+        data_tail = (yield)  # read report with the rest of checksum
+        data_footer += data_tail[:MSG_FOOTER_LEN - len(data_footer)]
+
+    data_checksum, = _parse_footer(data_footer)
+    if data_checksum != checksum:
+        target.throw(MessageChecksumError, 'Message checksum mismatch')
+    else:
+        target.throw(EOFError)
+
+
+def _encode_message(target):
+    pass