all: rework passphrase

The `on_device` field is being moved to PassphraseAck, State messages
are removed. Features newly contain `session_id`.

common/protob/messages-common.proto

@@ -110,31 +110,16 @@ message PinMatrixAck {
  * @next PassphraseAck
  */
 message PassphraseRequest {
-    optional bool on_device = 1;    // passphrase is being entered on the device
+    optional bool _deprecated_on_device = 1;  // moved to PassphraseAck but left for backwards compatibility
 }
 
 /**
  * Request: Send passphrase back
- * @next PassphraseStateRequest
+ * @auxend
  */
 message PassphraseAck {
     optional string passphrase = 1;
-    optional bytes state = 2;       // expected device state
-}
-
-/**
- * Response: Device awaits passphrase state
- * @next PassphraseStateAck
- */
-message PassphraseStateRequest {
-    optional bytes state = 1;       // actual device state
-}
-
-/**
- * Request: Send passphrase state back
- * @auxend
- */
-message PassphraseStateAck {
+    optional bool on_device = 2;    // user wants to enter passphrase on the device
 }
 
 /**

common/protob/messages-management.proto

@@ -20,8 +20,7 @@ enum BackupType {
  * @next Features
  */
 message Initialize {
-    optional bytes state = 1;           // assumed device state, clear session if set and different
-    optional bool skip_passphrase = 2;  // this session should always assume empty passphrase
+    optional bytes session_id = 1;           // assumed device session id; Trezor clears caches if it is different or empty
 }
 
 /**
@@ -88,6 +87,7 @@ message Features {
     optional bool sd_card_present = 32;         // is SD card present
     optional bool sd_protection = 33;           // is SD Protect enabled
     optional bool wipe_code_protection = 34;    // is wipe code protection enabled
+    optional bytes session_id = 35;
 }
 
 /**

common/protob/messages.proto

@@ -54,8 +54,8 @@ enum MessageType {
     MessageType_EntropyAck = 36 [(wire_in) = true];
     MessageType_PassphraseRequest = 41 [(wire_out) = true];
     MessageType_PassphraseAck = 42 [(wire_in) = true, (wire_tiny) = true, (wire_no_fsm) = true];
-    MessageType_PassphraseStateRequest = 77 [(wire_out) = true];
-    MessageType_PassphraseStateAck = 78 [(wire_in) = true, (wire_tiny) = true, (wire_no_fsm) = true];
+//    PassphraseStateRequest = 77  DEPRECATED
+//    PassphraseStateAck = 78  DEPRECATED
     MessageType_RecoveryDevice = 45 [(wire_in) = true];
     MessageType_WordRequest = 46 [(wire_out) = true];
     MessageType_WordAck = 47 [(wire_in) = true];

core/src/apps/cardano/seed.py

@@ -1,11 +1,15 @@
 import storage
-import storage.cache
 from trezor import wire
 from trezor.crypto import bip32
 
 from apps.cardano import CURVE, SEED_NAMESPACE
 from apps.common import mnemonic
-from apps.common.request_passphrase import protect_by_passphrase
+from apps.common.passphrase import get as get_passphrase
+
+if False:
+    from typing import Optional
+
+_cached_root = None  # type: Optional[bytes]
 
 
 class Keychain:
@@ -30,34 +34,26 @@ class Keychain:
         return node
 
 
-async def _get_passphrase(ctx: wire.Context) -> bytes:
-    passphrase = storage.cache.get_passphrase()
-    if passphrase is None:
-        passphrase = await protect_by_passphrase(ctx)
-        storage.cache.set_passphrase(passphrase)
-
-    return passphrase
-
-
 async def get_keychain(ctx: wire.Context) -> Keychain:
+    global _cached_root
+
     if not storage.is_initialized():
         raise wire.NotInitialized("Device is not initialized")
 
+    if _cached_root is None:
+        passphrase = await get_passphrase(ctx)
         if mnemonic.is_bip39():
             # derive the root node from mnemonic and passphrase
-        passphrase = await _get_passphrase(ctx)
-        root = bip32.from_mnemonic_cardano(mnemonic.get_secret().decode(), passphrase)
+            _cached_root = bip32.from_mnemonic_cardano(
+                mnemonic.get_secret().decode(), passphrase
+            )
         else:
-        seed = storage.cache.get_seed()
-        if seed is None:
-            passphrase = await _get_passphrase(ctx)
             seed = mnemonic.get_seed(passphrase)
-            storage.cache.set_seed(seed)
-        root = bip32.from_seed(seed, "ed25519 cardano seed")
+            _cached_root = bip32.from_seed(seed, "ed25519 cardano seed")
 
     # derive the namespaced root node
     for i in SEED_NAMESPACE:
-        root.derive_cardano(i)
+        _cached_root.derive_cardano(i)
 
-    keychain = Keychain(SEED_NAMESPACE, root)
+    keychain = Keychain(SEED_NAMESPACE, _cached_root)
     return keychain

core/src/apps/common/passphrase.py

@@ -0,0 +1,55 @@
+from micropython import const
+
+import storage.device
+from trezor import wire
+from trezor.messages.PassphraseAck import PassphraseAck
+from trezor.messages.PassphraseRequest import PassphraseRequest
+from trezor.ui.passphrase import CANCELLED, PassphraseKeyboard
+
+if __debug__:
+    from apps.debug import input_signal
+
+_MAX_PASSPHRASE_LEN = const(50)
+
+
+def is_enabled() -> bool:
+    return storage.device.is_passphrase_enabled()
+
+
+async def get(ctx: wire.Context) -> str:
+    if is_enabled():
+        return await request_from_user(ctx)
+    else:
+        return ""
+
+
+async def request_from_user(ctx: wire.Context) -> str:
+    request = PassphraseRequest()
+    ack = await ctx.call(request, PassphraseAck)
+    if ack.on_device:
+        if ack.passphrase is not None:
+            raise wire.ProcessError("Passphrase provided when it should not be")
+        passphrase = await request_from_user_on_device(ctx)
+    else:
+        if ack.passphrase is None:
+            raise wire.ProcessError("Passphrase not provided")
+        passphrase = ack.passphrase
+
+    if len(passphrase) > _MAX_PASSPHRASE_LEN:
+        raise wire.DataError("Maximum passphrase length is %d" % _MAX_PASSPHRASE_LEN)
+
+    return passphrase
+
+
+async def request_from_user_on_device(ctx: wire.Context) -> str:
+    keyboard = PassphraseKeyboard("Enter passphrase", _MAX_PASSPHRASE_LEN)
+    if __debug__:
+        passphrase = await ctx.wait(keyboard, input_signal())
+    else:
+        passphrase = await ctx.wait(keyboard)
+    if passphrase is CANCELLED:
+        raise wire.ActionCancelled("Passphrase entry cancelled")
+
+    assert isinstance(passphrase, str)
+
+    return passphrase

core/src/apps/common/request_passphrase.py

@@ -1,86 +0,0 @@
-from micropython import const
-
-import storage.device
-from storage import cache
-from trezor import ui, wire
-from trezor.messages import ButtonRequestType, PassphraseSourceType
-from trezor.messages.ButtonAck import ButtonAck
-from trezor.messages.ButtonRequest import ButtonRequest
-from trezor.messages.PassphraseAck import PassphraseAck
-from trezor.messages.PassphraseRequest import PassphraseRequest
-from trezor.messages.PassphraseStateAck import PassphraseStateAck
-from trezor.messages.PassphraseStateRequest import PassphraseStateRequest
-from trezor.ui.passphrase import CANCELLED, PassphraseKeyboard, PassphraseSource
-from trezor.ui.popup import Popup
-from trezor.ui.text import Text
-
-if __debug__:
-    from apps.debug import input_signal
-
-_MAX_PASSPHRASE_LEN = const(50)
-
-
-async def protect_by_passphrase(ctx: wire.Context) -> str:
-    if storage.device.has_passphrase():
-        return await request_passphrase(ctx)
-    else:
-        return ""
-
-
-async def request_passphrase(ctx: wire.Context) -> str:
-    source = storage.device.get_passphrase_source()
-    if source == PassphraseSourceType.ASK:
-        source = await request_passphrase_source(ctx)
-    passphrase = await request_passphrase_ack(
-        ctx, source == PassphraseSourceType.DEVICE
-    )
-    if len(passphrase) > _MAX_PASSPHRASE_LEN:
-        raise wire.DataError("Maximum passphrase length is %d" % _MAX_PASSPHRASE_LEN)
-    return passphrase
-
-
-async def request_passphrase_source(ctx: wire.Context) -> int:
-    req = ButtonRequest(code=ButtonRequestType.PassphraseType)
-    await ctx.call(req, ButtonAck)
-
-    text = Text("Enter passphrase", ui.ICON_CONFIG)
-    text.normal("Where do you want to", "enter your passphrase?")
-    source = PassphraseSource(text)
-
-    response = await ctx.wait(source)
-    assert isinstance(response, int)
-    return response
-
-
-async def request_passphrase_ack(ctx: wire.Context, on_device: bool) -> str:
-    if not on_device:
-        text = Text("Passphrase entry", ui.ICON_CONFIG)
-        text.normal("Please type your", "passphrase on the", "connected host.")
-        await Popup(text)
-
-    passphrase_request = PassphraseRequest(on_device=on_device)
-    ack = await ctx.call(passphrase_request, PassphraseAck)
-
-    if on_device:
-        if ack.passphrase is not None:
-            raise wire.ProcessError("Passphrase provided when it should not be")
-
-        keyboard = PassphraseKeyboard("Enter passphrase", _MAX_PASSPHRASE_LEN)
-        if __debug__:
-            passphrase = await ctx.wait(keyboard, input_signal())
-        else:
-            passphrase = await ctx.wait(keyboard)
-        if passphrase is CANCELLED:
-            raise wire.ActionCancelled("Passphrase cancelled")
-    else:
-        if ack.passphrase is None:
-            raise wire.ProcessError("Passphrase not provided")
-        passphrase = ack.passphrase
-
-    assert isinstance(passphrase, str)
-
-    state = cache.get_state(prev_state=ack.state, passphrase=passphrase)
-    state_request = PassphraseStateRequest(state=state)
-    await ctx.call(state_request, PassphraseStateAck)
-
-    return passphrase

core/src/apps/common/seed.py

@@ -5,7 +5,7 @@ from trezor.crypto import bip32, hashlib, hmac
 from trezor.crypto.curve import secp256k1
 
 from apps.common import HARDENED, mnemonic
-from apps.common.request_passphrase import protect_by_passphrase
+from apps.common.passphrase import get as get_passphrase
 
 if False:
     from typing import List, Union
@@ -114,10 +114,7 @@ async def get_keychain(ctx: wire.Context, namespaces: list) -> Keychain:
         raise wire.NotInitialized("Device is not initialized")
     seed = storage.cache.get_seed()
     if seed is None:
-        passphrase = storage.cache.get_passphrase()
-        if passphrase is None:
-            passphrase = await protect_by_passphrase(ctx)
-            storage.cache.set_passphrase(passphrase)
+        passphrase = await get_passphrase(ctx)
         seed = mnemonic.get_seed(passphrase)
         storage.cache.set_seed(seed)
     keychain = Keychain(seed, namespaces)

core/src/apps/debug/__init__.py

@@ -97,13 +97,12 @@ if __debug__:
         ctx: wire.Context, msg: DebugLinkGetState
     ) -> DebugLinkState:
         from trezor.messages.DebugLinkState import DebugLinkState
-        from storage.device import has_passphrase
-        from apps.common import mnemonic
+        from apps.common import mnemonic, passphrase
 
         m = DebugLinkState()
         m.mnemonic_secret = mnemonic.get_secret()
         m.mnemonic_type = mnemonic.get_type()
-        m.passphrase_protection = has_passphrase()
+        m.passphrase_protection = passphrase.is_enabled()
         m.reset_entropy = reset_internal_entropy
 
         if msg.wait_layout or current_content is None:

core/src/apps/homescreen/__init__.py

@@ -34,8 +34,8 @@ def get_features() -> Features:
     f.initialized = storage.is_initialized()
     f.pin_protection = config.has_pin()
     f.pin_cached = config.has_pin()
-    f.passphrase_protection = storage.device.has_passphrase()
-    f.passphrase_cached = cache.has_passphrase()
+    f.passphrase_protection = storage.device.is_passphrase_enabled()
+    # f.passphrase_cached = cache.has_passphrase()  # TODO
     f.needs_backup = storage.device.needs_backup()
     f.unfinished_backup = storage.device.unfinished_backup()
     f.no_backup = storage.device.no_backup()
@@ -71,14 +71,13 @@ def get_features() -> Features:
     f.sd_card_present = io.SDCard().present()
     f.sd_protection = storage.sd_salt.is_enabled()
     f.wipe_code_protection = config.has_wipe_code()
+    f.session_id = cache.get_session_id()
     return f
 
 
 async def handle_Initialize(ctx: wire.Context, msg: Initialize) -> Features:
-    if msg.state is None or msg.state != cache.get_state(prev_state=bytes(msg.state)):
+    if msg.session_id is None or msg.session_id != cache.get_session_id():
         cache.clear()
-        if msg.skip_passphrase:
-            cache.set_passphrase("")
     return get_features()
 
 
@@ -91,7 +90,7 @@ async def handle_Cancel(ctx: wire.Context, msg: Cancel) -> NoReturn:
 
 
 async def handle_ClearSession(ctx: wire.Context, msg: ClearSession) -> Success:
-    cache.clear(keep_passphrase=True)
+    cache.clear()
     return Success(message="Session cleared")
 
 
@@ -102,10 +101,10 @@ async def handle_Ping(ctx: wire.Context, msg: Ping) -> Success:
         from trezor.ui.text import Text
 
         await require_confirm(ctx, Text("Confirm"), ProtectCall)
-    if msg.passphrase_protection:
-        from apps.common.request_passphrase import protect_by_passphrase
+    if msg.passphrase_protection:  # TODO
+        from apps.common import passphrase
 
-        await protect_by_passphrase(ctx)
+        await passphrase.get(ctx)
     return Success(message=msg.message)
 
 

core/src/storage/cache.py

@@ -1,55 +1,18 @@
-from storage.device import get_device_id
-from trezor.crypto import hashlib, hmac, random
+from trezor.crypto import random
 
 if False:
     from typing import Optional
 
 _cached_seed = None  # type: Optional[bytes]
-_cached_seed_without_passphrase = None  # type: Optional[bytes]
-_cached_passphrase = None  # type: Optional[str]
-_cached_passphrase_fprint = b"\x00\x00\x00\x00"  # type: bytes
+_cached_seed_without_passphrase = None  # type: Optional[bytes]  # Needed for SLIP-21
+_cached_session_id = None  # type: Optional[bytes]
 
 
-def get_state(prev_state: bytes = None, passphrase: str = None) -> Optional[bytes]:
-    if prev_state is None:
-        salt = random.bytes(32)  # generate a random salt if no state provided
-    else:
-        salt = prev_state[:32]  # use salt from provided state
-        if len(salt) != 32:
-            return None  # invalid state
-    if passphrase is None:
-        if _cached_passphrase is None:
-            return None  # we don't have any passphrase to compute the state
-        else:
-            passphrase = _cached_passphrase  # use cached passphrase
-    return _compute_state(salt, passphrase)
-
-
-def _compute_state(salt: bytes, passphrase: str) -> bytes:
-    # state = HMAC(passphrase, salt || device_id)
-    message = salt + get_device_id().encode()
-    state = hmac.new(passphrase.encode(), message, hashlib.sha256).digest()
-    return salt + state
-
-
-def get_seed() -> Optional[bytes]:
-    return _cached_seed
-
-
-def get_seed_without_passphrase() -> Optional[bytes]:
-    return _cached_seed_without_passphrase
-
-
-def get_passphrase() -> Optional[str]:
-    return _cached_passphrase
-
-
-def get_passphrase_fprint() -> bytes:
-    return _cached_passphrase_fprint
-
-
-def has_passphrase() -> bool:
-    return _cached_passphrase is not None
+def get_session_id() -> Optional[bytes]:
+    global _cached_session_id
+    if not _cached_session_id:
+        _cached_session_id = random.bytes(32)
+    return _cached_session_id
 
 
 def set_seed(seed: Optional[bytes]) -> None:
@@ -57,19 +20,22 @@ def set_seed(seed: Optional[bytes]) -> None:
     _cached_seed = seed
 
 
+def get_seed() -> Optional[bytes]:
+    return _cached_seed
+
+
 def set_seed_without_passphrase(seed: Optional[bytes]) -> None:
     global _cached_seed_without_passphrase
     _cached_seed_without_passphrase = seed
 
 
-def set_passphrase(passphrase: Optional[str]) -> None:
-    global _cached_passphrase, _cached_passphrase_fprint
-    _cached_passphrase = passphrase
-    _cached_passphrase_fprint = _compute_state(b"FPRINT", passphrase or "")[:4]
+def get_seed_without_passphrase() -> Optional[bytes]:
+    return _cached_seed_without_passphrase
 
 
-def clear(keep_passphrase: bool = False) -> None:
+def clear() -> None:
+    global _cached_session_id
+    _cached_session_id = None
+
     set_seed(None)
     set_seed_without_passphrase(None)
-    if not keep_passphrase:
-        set_passphrase(None)

core/src/storage/device.py

@@ -101,7 +101,7 @@ def get_backup_type() -> EnumTypeBackupType:
     return backup_type  # type: ignore
 
 
-def has_passphrase() -> bool:
+def is_passphrase_enabled() -> bool:
     return common.get_bool(_NAMESPACE, _USE_PASSPHRASE)
 
 

core/src/trezor/messages/Features.py

@@ -50,6 +50,7 @@ class Features(p.MessageType):
         sd_card_present: bool = None,
         sd_protection: bool = None,
         wipe_code_protection: bool = None,
+        session_id: bytes = None,
     ) -> None:
         self.vendor = vendor
         self.major_version = major_version
@@ -84,6 +85,7 @@ class Features(p.MessageType):
         self.sd_card_present = sd_card_present
         self.sd_protection = sd_protection
         self.wipe_code_protection = wipe_code_protection
+        self.session_id = session_id
 
     @classmethod
     def get_fields(cls) -> Dict:
@@ -121,4 +123,5 @@ class Features(p.MessageType):
             32: ('sd_card_present', p.BoolType, 0),
             33: ('sd_protection', p.BoolType, 0),
             34: ('wipe_code_protection', p.BoolType, 0),
+            35: ('session_id', p.BytesType, 0),
         }

core/src/trezor/messages/Initialize.py

@@ -15,15 +15,12 @@ class Initialize(p.MessageType):
 
     def __init__(
         self,
-        state: bytes = None,
-        skip_passphrase: bool = None,
+        session_id: bytes = None,
     ) -> None:
-        self.state = state
-        self.skip_passphrase = skip_passphrase
+        self.session_id = session_id
 
     @classmethod
     def get_fields(cls) -> Dict:
         return {
-            1: ('state', p.BytesType, 0),
-            2: ('skip_passphrase', p.BoolType, 0),
+            1: ('session_id', p.BytesType, 0),
         }

core/src/trezor/messages/MessageType.py

@@ -29,8 +29,6 @@ EntropyRequest = 35  # type: Literal[35]
 EntropyAck = 36  # type: Literal[36]
 PassphraseRequest = 41  # type: Literal[41]
 PassphraseAck = 42  # type: Literal[42]
-PassphraseStateRequest = 77  # type: Literal[77]
-PassphraseStateAck = 78  # type: Literal[78]
 RecoveryDevice = 45  # type: Literal[45]
 WordRequest = 46  # type: Literal[46]
 WordAck = 47  # type: Literal[47]

core/src/trezor/messages/PassphraseAck.py

@@ -16,14 +16,14 @@ class PassphraseAck(p.MessageType):
     def __init__(
         self,
         passphrase: str = None,
-        state: bytes = None,
+        on_device: bool = None,
     ) -> None:
         self.passphrase = passphrase
-        self.state = state
+        self.on_device = on_device
 
     @classmethod
     def get_fields(cls) -> Dict:
         return {
             1: ('passphrase', p.UnicodeType, 0),
-            2: ('state', p.BytesType, 0),
+            2: ('on_device', p.BoolType, 0),
         }

core/src/trezor/messages/PassphraseRequest.py

@@ -15,12 +15,12 @@ class PassphraseRequest(p.MessageType):
 
     def __init__(
         self,
-        on_device: bool = None,
+        _deprecated_on_device: bool = None,
     ) -> None:
-        self.on_device = on_device
+        self._deprecated_on_device = _deprecated_on_device
 
     @classmethod
     def get_fields(cls) -> Dict:
         return {
-            1: ('on_device', p.BoolType, 0),
+            1: ('_deprecated_on_device', p.BoolType, 0),
         }

core/src/trezor/messages/PassphraseStateAck.py

@@ -1,14 +0,0 @@
-# Automatically generated by pb2py
-# fmt: off
-import protobuf as p
-
-if __debug__:
-    try:
-        from typing import Dict, List  # noqa: F401
-        from typing_extensions import Literal  # noqa: F401
-    except ImportError:
-        pass
-
-
-class PassphraseStateAck(p.MessageType):
-    MESSAGE_WIRE_TYPE = 78

core/src/trezor/messages/PassphraseStateRequest.py

@@ -1,26 +0,0 @@
-# Automatically generated by pb2py
-# fmt: off
-import protobuf as p
-
-if __debug__:
-    try:
-        from typing import Dict, List  # noqa: F401
-        from typing_extensions import Literal  # noqa: F401
-    except ImportError:
-        pass
-
-
-class PassphraseStateRequest(p.MessageType):
-    MESSAGE_WIRE_TYPE = 77
-
-    def __init__(
-        self,
-        state: bytes = None,
-    ) -> None:
-        self.state = state
-
-    @classmethod
-    def get_fields(cls) -> Dict:
-        return {
-            1: ('state', p.BytesType, 0),
-        }

docs/communication/index.md

@@ -0,0 +1,9 @@
+# Communication
+
+_Note: In this section we describe the internal functioning of the communication protocol. If you wish to implement Trezor support you should use [Connect](https://github.com/trezor/connect/) or [python-trezor](https://pypi.org/project/trezor/), which will do all this hard work for you._
+
+We use [Protobuf v2](https://developers.google.com/protocol-buffers/) for host-device communication. The communication cycle is very simple, Trezor receives a message (request), acts on it and responds with another one (response). Trezor on its own is incapable of initiating the communication.
+
+## Definitions
+
+Protobuf messages are defined in the [Common](https://github.com/trezor/trezor-firmware/tree/master/common) project, which is part of this monorepo. This repository is also exported to [trezor/trezor-common](https://github.com/trezor/trezor-common) to be used by third parties, which prefer not to include the whole monorepo. That copy is read-only mirror and all changes are happening in this monorepo.

docs/communication/passphrase.md

@@ -0,0 +1,64 @@
+# Passphrase 
+
+As of \[versions TBD\] we have changed how [passphrase](https://wiki.trezor.io/Passphrase) is communicated between the Host and the Device.
+ 
+Passphrase is very tightly coupled with _sessions_. The reader is encouraged to read on that topic first in the [sessions.md](sessions.md) section.
+
+## Scheme
+
+As soon as Trezor needs the passphrase to do BIP-39/SLIP-39 derivations it prompts the user for passphrase.
+
+```
+GetAddress(...) 
+--------->          PassphraseRequest()
+                       <---------
+PassphraseAck
+(str passphrase, bool on_device)  
+--------->          Address(...)
+                       <---------
+```
+
+In the default Trezor setting, the passphrase is obtained from the Host. Trezor sends a PassphraseRequest message and awaits PassphraseAck as a response. This message contains field `passphrase` to transmit it or it has `on_device` boolean flag to indicate that the user wishes to enter the passphrase on Trezor instead. Setting both `passphrase` and `on_device` to true is forbidden.
+
+Note that this has changed as of TBD. In previous firmware versions the `on_device` flag was in the PassphraseRequest message, since this decision has been made on Trezor. We also had two additional messages PassphraseStateRequest and PassphraseStateAck which were removed.
+
+## Example
+
+On an initialized device with passphrase enabled a common communication starts like this:
+
+```
+Initialize()
+--------->          Features(..., session_id)
+                       <---------
+GetAddress(...) 
+--------->          PassphraseRequest()
+                       <---------
+PassphraseAck(...)
+--------->          Address(...)
+                       <---------
+```
+
+The device requested the passphrase since the BIP-39/SLIP-39 seed is not yet cached. After this workflow the seed is cached and the passphrase will therefore never be requested again unless the session is cleared*. 
+
+Since we do not have sessions, the Host can not be sure that someone else has not used the device and applied another session id (e.g. changed the Passphrase). To work around this we send the session id again on every subsequent message. See more on that in [session.md]().
+
+```
+Initialize(session_id)
+--------->          Features(..., session_id)
+                       <---------
+GetPublicKey(...) 
+--------->          PublicKey(...)
+                       <---------
+```
+
+As long as the session_id in `Initialize` is the same as the one Trezor stores internally, Trezor guarantees the same passphrase is being used.
+
+----
+
+\* There is one exception and that is Cardano. Because Cardano has a different BIP-39/SLIP-39 derivation scheme for passphrase we can not use the cached seed. As a workaround we prompt for the passphrase again in such case and cache the cardano seed in the cardano app directly.
+
+## Passphrase always on device
+
+User might want to enforce the passphrase entry on the device every time without the hassle of instructing the Host to do so.
+
+For such cases the user may apply the *Passphrase always on device* setting TODO: Name. As the name suggests, with this setting the passphrase is prompted on the device right away and no PassphraseRequest/PassphraseAck messages are exchanged.

docs/communication/sessions.md

@@ -0,0 +1,36 @@
+# Sessions (the lack of them)
+
+Currently the communication protocol lacks sessions, which are planned to be introduced in the near future (see [#79](https://github.com/trezor/trezor-firmware/issues/79)).
+
+To ensure the device is in the expected state we use something called _session_id_. Session id is a 32 bytes long random blob which identifies the internal device state (mainly its caches). This is primarily useful for passphrase to make sure the same passphrase is cached in the device as the one the user entered a few minutes ago. See [passphrase.md](passphrase.md) for more on that.
+
+On first initialization the Host does not have a session id and starts the communication with an empty Initialize:
+
+```
+Initialize()
+--------->          Features(..., session_id)
+                       <---------
+```
+
+After the first Features message is received the Host might store the session_id. To ensure the device state Host must send the Initialize message again including that particular session_id:
+
+```
+Initialize(session_id) 
+--------->          Features(..., session_id)
+                       <---------
+Request
+--------->          Response
+                       <---------
+```
+
+So to make sure the device state has not changed, the Host must send the Initialize message with the correctly stored session_id before each request. Yes, this is stupid.
+
+As mentioned, sessions will be introduced soon™ and fix that. We will probably take the first few bytes of the session_id, declare it a session id, and the rest will remain, without the annoying requirement of sending Initialize before every message.
+
+----
+
+The session is terminated and therefore the caches are cleared if:
+- Initialize.session_id is empty.
+- Initialize.session_id is different then the one cached in Trezor.
+- Trezor is replugged (session is not persistent).
+- ClearSession is received.

python/src/trezorlib/cli/trezorctl.py

@@ -141,9 +141,16 @@ def configure_logging(verbose: int):
 @click.option(
     "-j", "--json", "is_json", is_flag=True, help="Print result as JSON object"
 )
+@click.option(
+    "-P",
+    "--passphrase-on-host",
+    "passphrase_on_host",
+    is_flag=True,
+    help="Enter passphrase on host.",
+)
 @click.version_option()
 @click.pass_context
-def cli(ctx, path, verbose, is_json):
+def cli(ctx, path, verbose, is_json, passphrase_on_host):
     configure_logging(verbose)
 
     def get_device():
@@ -157,13 +164,15 @@ def cli(ctx, path, verbose, is_json):
                 if path is not None:
                     click.echo("Using path: {}".format(path))
                 sys.exit(1)
-        return TrezorClient(transport=device, ui=ui.ClickUI())
+        return TrezorClient(
+            transport=device, ui=ui.ClickUI(), passphrase_on_host=passphrase_on_host
+        )
 
     ctx.obj = get_device
 
 
 @cli.resultcallback()
-def print_result(res, path, verbose, is_json):
+def print_result(res, path, verbose, is_json, passphrase_on_host):
     if is_json:
         if isinstance(res, protobuf.MessageType):
             click.echo(json.dumps({res.__class__.__name__: res.__dict__}))

python/src/trezorlib/client.py

@@ -107,15 +107,21 @@ class TrezorClient:
     - passphrase request (ask the user to enter a passphrase)
     See `trezorlib.ui` for details.
 
-    You can supply a `state` you saved in the previous session. If you do,
-    the user might not need to enter their passphrase again.
+    You can supply a `session_id` you might have saved in the previous session.
+    If you do, the user might not need to enter their passphrase again.
+
+    Set `passphrase_on_host` to True if you want to enter passphrase on host directly
+    instead of on Trezor.
     """
 
-    def __init__(self, transport, ui=_NO_UI_OBJECT, state=None):
+    def __init__(
+        self, transport, ui=_NO_UI_OBJECT, session_id=None, passphrase_on_host=False
+    ):
         LOG.info("creating client instance for device: {}".format(transport.get_path()))
         self.transport = transport
         self.ui = ui
-        self.state = state
+        self.session_id = session_id
+        self.passphrase_on_host = passphrase_on_host
 
         # XXX remove when old Electrum has been cycled out.
         # explanation: We changed the API in 0.11 and this broke older versions
@@ -177,10 +183,9 @@ class TrezorClient:
         else:
             return resp
 
-    def _callback_passphrase(self, msg):
-        if msg.on_device:
-            passphrase = None
-        else:
+    def _callback_passphrase(self, msg: messages.PassphraseRequest):
+        if self.passphrase_on_host:
+            on_device = False
             try:
                 passphrase = self.ui.get_passphrase()
             except exceptions.Cancelled:
@@ -191,16 +196,13 @@ class TrezorClient:
             if len(passphrase) > MAX_PASSPHRASE_LENGTH:
                 self.call_raw(messages.Cancel())
                 raise ValueError("Passphrase too long")
-
-        resp = self.call_raw(
-            messages.PassphraseAck(passphrase=passphrase, state=self.state)
-        )
-        if isinstance(resp, messages.PassphraseStateRequest):
-            # TODO report to the user that the passphrase has changed?
-            self.state = resp.state
-            return self.call_raw(messages.PassphraseStateAck())
         else:
-            return resp
+            on_device = True
+            passphrase = None
+
+        return self.call_raw(
+            messages.PassphraseAck(passphrase=passphrase, on_device=on_device)
+        )
 
     def _callback_button(self, msg):
         __tracebackhide__ = True  # for pytest # pylint: disable=W0612
@@ -229,7 +231,7 @@ class TrezorClient:
 
     @tools.session
     def init_device(self):
-        resp = self.call_raw(messages.Initialize(state=self.state))
+        resp = self.call_raw(messages.Initialize(session_id=self.session_id))
         if not isinstance(resp, messages.Features):
             raise exceptions.TrezorException("Unexpected initial response")
         else:
@@ -245,6 +247,8 @@ class TrezorClient:
             self.features.patch_version,
         )
         self.check_firmware_version(warn_only=True)
+        if self.version >= (2, 1, 9):
+            self.session_id = self.features.session_id
 
     def is_outdated(self):
         if self.features.bootloader_mode:
@@ -295,7 +299,7 @@ class TrezorClient:
     def clear_session(self):
         resp = self.call_raw(messages.ClearSession())
         if isinstance(resp, messages.Success):
-            self.state = None
+            self.session_id = None
             self.init_device()
             return resp.message
         else:

python/src/trezorlib/messages/Features.py

@@ -50,6 +50,7 @@ class Features(p.MessageType):
         sd_card_present: bool = None,
         sd_protection: bool = None,
         wipe_code_protection: bool = None,
+        session_id: bytes = None,
     ) -> None:
         self.vendor = vendor
         self.major_version = major_version
@@ -84,6 +85,7 @@ class Features(p.MessageType):
         self.sd_card_present = sd_card_present
         self.sd_protection = sd_protection
         self.wipe_code_protection = wipe_code_protection
+        self.session_id = session_id
 
     @classmethod
     def get_fields(cls) -> Dict:
@@ -121,4 +123,5 @@ class Features(p.MessageType):
             32: ('sd_card_present', p.BoolType, 0),
             33: ('sd_protection', p.BoolType, 0),
             34: ('wipe_code_protection', p.BoolType, 0),
+            35: ('session_id', p.BytesType, 0),
         }

python/src/trezorlib/messages/Initialize.py

@@ -15,15 +15,12 @@ class Initialize(p.MessageType):
 
     def __init__(
         self,
-        state: bytes = None,
-        skip_passphrase: bool = None,
+        session_id: bytes = None,
     ) -> None:
-        self.state = state
-        self.skip_passphrase = skip_passphrase
+        self.session_id = session_id
 
     @classmethod
     def get_fields(cls) -> Dict:
         return {
-            1: ('state', p.BytesType, 0),
-            2: ('skip_passphrase', p.BoolType, 0),
+            1: ('session_id', p.BytesType, 0),
         }

python/src/trezorlib/messages/MessageType.py

@@ -27,8 +27,6 @@ EntropyRequest = 35  # type: Literal[35]
 EntropyAck = 36  # type: Literal[36]
 PassphraseRequest = 41  # type: Literal[41]
 PassphraseAck = 42  # type: Literal[42]
-PassphraseStateRequest = 77  # type: Literal[77]
-PassphraseStateAck = 78  # type: Literal[78]
 RecoveryDevice = 45  # type: Literal[45]
 WordRequest = 46  # type: Literal[46]
 WordAck = 47  # type: Literal[47]

python/src/trezorlib/messages/PassphraseAck.py

@@ -16,14 +16,14 @@ class PassphraseAck(p.MessageType):
     def __init__(
         self,
         passphrase: str = None,
-        state: bytes = None,
+        on_device: bool = None,
     ) -> None:
         self.passphrase = passphrase
-        self.state = state
+        self.on_device = on_device
 
     @classmethod
     def get_fields(cls) -> Dict:
         return {
             1: ('passphrase', p.UnicodeType, 0),
-            2: ('state', p.BytesType, 0),
+            2: ('on_device', p.BoolType, 0),
         }

python/src/trezorlib/messages/PassphraseRequest.py

@@ -15,12 +15,12 @@ class PassphraseRequest(p.MessageType):
 
     def __init__(
         self,
-        on_device: bool = None,
+        _deprecated_on_device: bool = None,
     ) -> None:
-        self.on_device = on_device
+        self._deprecated_on_device = _deprecated_on_device
 
     @classmethod
     def get_fields(cls) -> Dict:
         return {
-            1: ('on_device', p.BoolType, 0),
+            1: ('_deprecated_on_device', p.BoolType, 0),
         }

python/src/trezorlib/messages/PassphraseStateAck.py

@@ -1,14 +0,0 @@
-# Automatically generated by pb2py
-# fmt: off
-from .. import protobuf as p
-
-if __debug__:
-    try:
-        from typing import Dict, List  # noqa: F401
-        from typing_extensions import Literal  # noqa: F401
-    except ImportError:
-        pass
-
-
-class PassphraseStateAck(p.MessageType):
-    MESSAGE_WIRE_TYPE = 78

python/src/trezorlib/messages/PassphraseStateRequest.py

@@ -1,26 +0,0 @@
-# Automatically generated by pb2py
-# fmt: off
-from .. import protobuf as p
-
-if __debug__:
-    try:
-        from typing import Dict, List  # noqa: F401
-        from typing_extensions import Literal  # noqa: F401
-    except ImportError:
-        pass
-
-
-class PassphraseStateRequest(p.MessageType):
-    MESSAGE_WIRE_TYPE = 77
-
-    def __init__(
-        self,
-        state: bytes = None,
-    ) -> None:
-        self.state = state
-
-    @classmethod
-    def get_fields(cls) -> Dict:
-        return {
-            1: ('state', p.BytesType, 0),
-        }

python/src/trezorlib/messages/__init__.py

@@ -194,8 +194,6 @@ from .NEMTransfer import NEMTransfer
 from .NextU2FCounter import NextU2FCounter
 from .PassphraseAck import PassphraseAck
 from .PassphraseRequest import PassphraseRequest
-from .PassphraseStateAck import PassphraseStateAck
-from .PassphraseStateRequest import PassphraseStateRequest
 from .PinMatrixAck import PinMatrixAck
 from .PinMatrixRequest import PinMatrixRequest
 from .Ping import Ping

tests/device_tests/test_basic.py

@@ -20,7 +20,7 @@ from trezorlib import device, messages
 class TestBasic:
     def test_features(self, client):
         f0 = client.features
-        f1 = client.call(messages.Initialize())
+        f1 = client.call(messages.Initialize(f0.session_id))
         assert f0 == f1
 
     def test_ping(self, client):

tests/device_tests/test_msg_cardano_sign_tx_slip39_basic.py

@@ -119,10 +119,7 @@ def test_cardano_sign_tx(
     inputs = [cardano.create_input(i) for i in inputs]
     outputs = [cardano.create_output(o) for o in outputs]
 
-    expected_responses = [
-        messages.PassphraseRequest(),
-        messages.PassphraseStateRequest(),
-    ]
+    expected_responses = [messages.PassphraseRequest()]
     expected_responses += [
         messages.CardanoTxRequest(tx_index=i) for i in range(len(transactions))
     ]

tests/device_tests/test_session_id.py

@@ -0,0 +1,123 @@
+# This file is part of the Trezor project.
+#
+# Copyright (C) 2012-2019 SatoshiLabs and contributors
+#
+# This library is free software: you can redistribute it and/or modify
+# it under the terms of the GNU Lesser General Public License version 3
+# as published by the Free Software Foundation.
+#
+# This library is distributed in the hope that it will be useful,
+# but WITHOUT ANY WARRANTY; without even the implied warranty of
+# MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+# GNU Lesser General Public License for more details.
+#
+# You should have received a copy of the License along with this library.
+# If not, see <https://www.gnu.org/licenses/lgpl-3.0.html>.
+
+import pytest
+
+from trezorlib import messages
+from trezorlib.tools import parse_path
+
+
+def _get_xpub(client, passphrase):
+    response = client.call_raw(
+        messages.GetPublicKey(address_n=parse_path("44'/0'/0'"), coin_name="Bitcoin")
+    )
+    if passphrase is not None:
+        assert isinstance(response, messages.PassphraseRequest)
+        response = client.call_raw(messages.PassphraseAck(passphrase=passphrase))
+    assert isinstance(response, messages.PublicKey)
+    return response.xpub
+
+
+@pytest.mark.skip_t1  # TODO
+@pytest.mark.setup_client(passphrase=True)
+def test_session_with_passphrase(client):
+    # Let's start the communication by calling Initialize.
+    response = client.call_raw(messages.Initialize())
+    assert isinstance(response, messages.Features)
+    session_id = response.session_id
+    assert len(session_id) == 32
+
+    # GetPublicKey requires passphrase and since it is not cached,
+    # Trezor will prompt for it.
+    xpub = _get_xpub(client, passphrase="A")
+    assert (
+        xpub
+        == "xpub6CekxGcnqnJ6osfY4Rrq7W5ogFtR54KUvz4H16XzaQuukMFZCGebEpVznfq4yFcKEmYyShwj2UKjL7CazuNSuhdkofF4mHabHkLxCMVvsqG"
+    )
+
+    # Call Initialize again, this time with the received session id and then call
+    # GetPublicKey. The passphrase should be cached now so Trezor must
+    # not ask for it again, whilst returning the same xpub.
+    response = client.call_raw(messages.Initialize(session_id=session_id))
+    assert isinstance(response, messages.Features)
+    xpub = _get_xpub(client, passphrase=None)
+    assert (
+        xpub
+        == "xpub6CekxGcnqnJ6osfY4Rrq7W5ogFtR54KUvz4H16XzaQuukMFZCGebEpVznfq4yFcKEmYyShwj2UKjL7CazuNSuhdkofF4mHabHkLxCMVvsqG"
+    )
+
+    # If we set session id in Initialize to None, the cache will be cleared
+    # and Trezor will ask for the passphrase again.
+    response = client.call_raw(messages.Initialize(session_id=None))
+    assert isinstance(response, messages.Features)
+    xpub = _get_xpub(client, passphrase="A")
+    assert (
+        xpub
+        == "xpub6CekxGcnqnJ6osfY4Rrq7W5ogFtR54KUvz4H16XzaQuukMFZCGebEpVznfq4yFcKEmYyShwj2UKjL7CazuNSuhdkofF4mHabHkLxCMVvsqG"
+    )
+
+    # Unknown session id is the same as setting it to None.
+    response = client.call_raw(messages.Initialize(session_id=b"X" * 32))
+    assert isinstance(response, messages.Features)
+    xpub = _get_xpub(client, passphrase="A")
+    assert (
+        xpub
+        == "xpub6CekxGcnqnJ6osfY4Rrq7W5ogFtR54KUvz4H16XzaQuukMFZCGebEpVznfq4yFcKEmYyShwj2UKjL7CazuNSuhdkofF4mHabHkLxCMVvsqG"
+    )
+
+
+@pytest.mark.skip_t1  # TODO
+@pytest.mark.setup_client()
+def test_session_enable_passphrase(client):
+    # Let's start the communication by calling Initialize.
+    response = client.call_raw(messages.Initialize())
+    assert isinstance(response, messages.Features)
+    session_id = response.session_id
+    assert len(session_id) == 32
+
+    # Trezor will not prompt for passphrase because it is turned off.
+    xpub = _get_xpub(client, passphrase=None)
+    assert (
+        xpub
+        == "xpub6BiVtCpG9fQPxnPmHXG8PhtzQdWC2Su4qWu6XW9tpWFYhxydCLJGrWBJZ5H6qTAHdPQ7pQhtpjiYZVZARo14qHiay2fvrX996oEP42u8wZy"
+    )
+
+    # Turn on passphrase.
+    response = client.call_raw(messages.ApplySettings(use_passphrase=True))
+    assert isinstance(response, messages.ButtonRequest)  # confirm dialog
+    client.debug.press_yes()
+    response = client.call_raw(messages.ButtonAck())
+    assert isinstance(response, messages.Success)
+
+    # The session id is unchanged, therefore we do not prompt for the passphrase.
+    response = client.call_raw(messages.Initialize(session_id=session_id))
+    xpub = _get_xpub(client, passphrase=None)
+    assert isinstance(response, messages.Features)
+    assert session_id == response.session_id
+    assert (
+        xpub
+        == "xpub6BiVtCpG9fQPxnPmHXG8PhtzQdWC2Su4qWu6XW9tpWFYhxydCLJGrWBJZ5H6qTAHdPQ7pQhtpjiYZVZARo14qHiay2fvrX996oEP42u8wZy"
+    )
+
+    # We clear the session id now, so the passphrase should be asked.
+    response = client.call_raw(messages.Initialize())
+    xpub = _get_xpub(client, passphrase="A")
+    assert isinstance(response, messages.Features)
+    assert session_id != response.session_id
+    assert (
+        xpub
+        == "xpub6CekxGcnqnJ6osfY4Rrq7W5ogFtR54KUvz4H16XzaQuukMFZCGebEpVznfq4yFcKEmYyShwj2UKjL7CazuNSuhdkofF4mHabHkLxCMVvsqG"
+    )