python-kasa/kasa/aestransport.py

"""Implementation of the TP-Link AES transport.

Based on the work of https://github.com/petretiandrea/plugp100
under compatible GNU GPL3 license.
"""

import base64
import hashlib
import logging
import time
from typing import TYPE_CHECKING, AsyncGenerator, Dict, Optional, cast

from cryptography.hazmat.primitives import padding, serialization
from cryptography.hazmat.primitives.asymmetric import padding as asymmetric_padding
from cryptography.hazmat.primitives.asymmetric import rsa
from cryptography.hazmat.primitives.ciphers import Cipher, algorithms, modes

from .credentials import Credentials
from .deviceconfig import DeviceConfig
from .exceptions import (
    SMART_AUTHENTICATION_ERRORS,
    SMART_RETRYABLE_ERRORS,
    SMART_TIMEOUT_ERRORS,
    AuthenticationException,
    RetryableException,
    SmartDeviceException,
    SmartErrorCode,
    TimeoutException,
)
from .httpclient import HttpClient
from .json import dumps as json_dumps
from .json import loads as json_loads
from .protocol import DEFAULT_CREDENTIALS, BaseTransport, get_default_credentials

_LOGGER = logging.getLogger(__name__)


def _sha1(payload: bytes) -> str:
    sha1_algo = hashlib.sha1()  # noqa: S324
    sha1_algo.update(payload)
    return sha1_algo.hexdigest()


class AesTransport(BaseTransport):
    """Implementation of the AES encryption protocol.

    AES is the name used in device discovery for TP-Link's TAPO encryption
    protocol, sometimes used by newer firmware versions on kasa devices.
    """

    DEFAULT_PORT: int = 80
    SESSION_COOKIE_NAME = "TP_SESSIONID"
    COMMON_HEADERS = {
        "Content-Type": "application/json",
        "requestByApp": "true",
        "Accept": "application/json",
    }
    CONTENT_LENGTH = "Content-Length"
    KEY_PAIR_CONTENT_LENGTH = 314

    def __init__(
        self,
        *,
        config: DeviceConfig,
    ) -> None:
        super().__init__(config=config)

        self._login_version = config.connection_type.login_version
        if (
            not self._credentials or self._credentials.username is None
        ) and not self._credentials_hash:
            self._credentials = Credentials()
        if self._credentials:
            self._login_params = self._get_login_params(self._credentials)
        else:
            self._login_params = json_loads(
                base64.b64decode(self._credentials_hash.encode()).decode()  # type: ignore[union-attr]
            )
        self._default_credentials: Optional[Credentials] = None
        self._http_client: HttpClient = HttpClient(config)

        self._handshake_done = False

        self._encryption_session: Optional[AesEncyptionSession] = None
        self._session_expire_at: Optional[float] = None

        self._session_cookie: Optional[Dict[str, str]] = None

        self._login_token = None

        self._key_pair: Optional[KeyPair] = None

        _LOGGER.debug("Created AES transport for %s", self._host)

    @property
    def default_port(self):
        """Default port for the transport."""
        return self.DEFAULT_PORT

    @property
    def credentials_hash(self) -> str:
        """The hashed credentials used by the transport."""
        return base64.b64encode(json_dumps(self._login_params).encode()).decode()

    def _get_login_params(self, credentials):
        """Get the login parameters based on the login_version."""
        un, pw = self.hash_credentials(self._login_version == 2, credentials)
        password_field_name = "password2" if self._login_version == 2 else "password"
        return {password_field_name: pw, "username": un}

    @staticmethod
    def hash_credentials(login_v2, credentials):
        """Hash the credentials."""
        if login_v2:
            un = base64.b64encode(
                _sha1(credentials.username.encode()).encode()
            ).decode()
            pw = base64.b64encode(
                _sha1(credentials.password.encode()).encode()
            ).decode()
        else:
            un = base64.b64encode(
                _sha1(credentials.username.encode()).encode()
            ).decode()
            pw = base64.b64encode(credentials.password.encode()).decode()
        return un, pw

    def _handle_response_error_code(self, resp_dict: dict, msg: str):
        error_code = SmartErrorCode(resp_dict.get("error_code"))  # type: ignore[arg-type]
        if error_code == SmartErrorCode.SUCCESS:
            return
        msg = f"{msg}: {self._host}: {error_code.name}({error_code.value})"
        if error_code in SMART_TIMEOUT_ERRORS:
            raise TimeoutException(msg, error_code=error_code)
        if error_code in SMART_RETRYABLE_ERRORS:
            raise RetryableException(msg, error_code=error_code)
        if error_code in SMART_AUTHENTICATION_ERRORS:
            self._handshake_done = False
            self._login_token = None
            raise AuthenticationException(msg, error_code=error_code)
        raise SmartDeviceException(msg, error_code=error_code)

    async def send_secure_passthrough(self, request: str):
        """Send encrypted message as passthrough."""
        url = f"http://{self._host}/app"
        if self._login_token:
            url += f"?token={self._login_token}"

        encrypted_payload = self._encryption_session.encrypt(request.encode())  # type: ignore
        passthrough_request = {
            "method": "securePassthrough",
            "params": {"request": encrypted_payload.decode()},
        }
        status_code, resp_dict = await self._http_client.post(
            url,
            json=passthrough_request,
            headers=self.COMMON_HEADERS,
            cookies_dict=self._session_cookie,
        )
        # _LOGGER.debug(f"secure_passthrough response is {status_code}: {resp_dict}")

        if status_code != 200:
            raise SmartDeviceException(
                f"{self._host} responded with an unexpected "
                + f"status code {status_code} to passthrough"
            )

        resp_dict = cast(Dict, resp_dict)
        self._handle_response_error_code(
            resp_dict, "Error sending secure_passthrough message"
        )

        response = self._encryption_session.decrypt(  # type: ignore
            resp_dict["result"]["response"].encode()
        )
        resp_dict = json_loads(response)
        return resp_dict

    async def perform_login(self):
        """Login to the device."""
        try:
            await self.try_login(self._login_params)
        except AuthenticationException as ex:
            if ex.error_code != SmartErrorCode.LOGIN_ERROR:
                raise ex
            if self._default_credentials is None:
                self._default_credentials = get_default_credentials(
                    DEFAULT_CREDENTIALS["TAPO"]
                )
            await self.perform_handshake()
            await self.try_login(self._get_login_params(self._default_credentials))
            _LOGGER.debug(
                "%s: logged in with default credentials",
                self._host,
            )

    async def try_login(self, login_params):
        """Try to login with supplied login_params."""
        self._login_token = None
        login_request = {
            "method": "login_device",
            "params": login_params,
            "request_time_milis": round(time.time() * 1000),
        }
        request = json_dumps(login_request)

        resp_dict = await self.send_secure_passthrough(request)
        self._handle_response_error_code(resp_dict, "Error logging in")
        self._login_token = resp_dict["result"]["token"]

    async def _generate_key_pair_payload(self) -> AsyncGenerator:
        """Generate the request body and return an ascyn_generator.

        This prevents the key pair being generated unless a connection
        can be made to the device.
        """
        _LOGGER.debug("Generating keypair")
        self._key_pair = KeyPair.create_key_pair()
        pub_key = (
            "-----BEGIN PUBLIC KEY-----\n"
            + self._key_pair.get_public_key()  # type: ignore[union-attr]
            + "\n-----END PUBLIC KEY-----\n"
        )
        handshake_params = {"key": pub_key}
        _LOGGER.debug(f"Handshake params: {handshake_params}")
        request_body = {"method": "handshake", "params": handshake_params}
        _LOGGER.debug(f"Request {request_body}")
        yield json_dumps(request_body).encode()

    async def perform_handshake(self):
        """Perform the handshake."""
        _LOGGER.debug("Will perform handshaking...")

        self._key_pair = None
        self._handshake_done = False
        self._session_expire_at = None
        self._session_cookie = None

        url = f"http://{self._host}/app"
        # Device needs the content length or it will response with 500
        headers = {
            **self.COMMON_HEADERS,
            self.CONTENT_LENGTH: str(self.KEY_PAIR_CONTENT_LENGTH),
        }
        status_code, resp_dict = await self._http_client.post(
            url,
            json=self._generate_key_pair_payload(),
            headers=headers,
            cookies_dict=self._session_cookie,
        )

        _LOGGER.debug(f"Device responded with: {resp_dict}")

        if status_code != 200:
            raise SmartDeviceException(
                f"{self._host} responded with an unexpected "
                + f"status code {status_code} to handshake"
            )

        self._handle_response_error_code(resp_dict, "Unable to complete handshake")

        handshake_key = resp_dict["result"]["key"]

        if (
            cookie := self._http_client.get_cookie(  # type: ignore
                self.SESSION_COOKIE_NAME
            )
        ) or (
            cookie := self._http_client.get_cookie(  # type: ignore
                "SESSIONID"
            )
        ):
            self._session_cookie = {self.SESSION_COOKIE_NAME: cookie}

        self._session_expire_at = time.time() + 86400
        if TYPE_CHECKING:
            assert self._key_pair is not None  # pragma: no cover
        self._encryption_session = AesEncyptionSession.create_from_keypair(
            handshake_key, self._key_pair
        )

        self._handshake_done = True

        _LOGGER.debug("Handshake with %s complete", self._host)

    def _handshake_session_expired(self):
        """Return true if session has expired."""
        return (
            self._session_expire_at is None
            or self._session_expire_at - time.time() <= 0
        )

    async def send(self, request: str):
        """Send the request."""
        if not self._handshake_done or self._handshake_session_expired():
            await self.perform_handshake()
        if not self._login_token:
            try:
                await self.perform_login()
            # After a login failure handshake needs to
            # be redone or a 9999 error is received.
            except AuthenticationException as ex:
                self._handshake_done = False
                raise ex

        return await self.send_secure_passthrough(request)

    async def close(self) -> None:
        """Mark the handshake and login as not done.

        Since we likely lost the connection.
        """
        self._handshake_done = False
        self._login_token = None


class AesEncyptionSession:
    """Class for an AES encryption session."""

    @staticmethod
    def create_from_keypair(handshake_key: str, keypair):
        """Create the encryption session."""
        handshake_key_bytes: bytes = base64.b64decode(handshake_key.encode("UTF-8"))
        private_key_data = base64.b64decode(keypair.get_private_key().encode("UTF-8"))

        private_key = serialization.load_der_private_key(private_key_data, None, None)
        key_and_iv = private_key.decrypt(
            handshake_key_bytes, asymmetric_padding.PKCS1v15()
        )
        if key_and_iv is None:
            raise ValueError("Decryption failed!")

        return AesEncyptionSession(key_and_iv[:16], key_and_iv[16:])

    def __init__(self, key, iv):
        self.cipher = Cipher(algorithms.AES(key), modes.CBC(iv))
        self.padding_strategy = padding.PKCS7(algorithms.AES.block_size)

    def encrypt(self, data) -> bytes:
        """Encrypt the message."""
        encryptor = self.cipher.encryptor()
        padder = self.padding_strategy.padder()
        padded_data = padder.update(data) + padder.finalize()
        encrypted = encryptor.update(padded_data) + encryptor.finalize()
        return base64.b64encode(encrypted)

    def decrypt(self, data) -> str:
        """Decrypt the message."""
        decryptor = self.cipher.decryptor()
        unpadder = self.padding_strategy.unpadder()
        decrypted = decryptor.update(base64.b64decode(data)) + decryptor.finalize()
        unpadded_data = unpadder.update(decrypted) + unpadder.finalize()
        return unpadded_data.decode()


class KeyPair:
    """Class for generating key pairs."""

    @staticmethod
    def create_key_pair(key_size: int = 1024):
        """Create a key pair."""
        private_key = rsa.generate_private_key(public_exponent=65537, key_size=key_size)
        public_key = private_key.public_key()

        private_key_bytes = private_key.private_bytes(
            encoding=serialization.Encoding.DER,
            format=serialization.PrivateFormat.PKCS8,
            encryption_algorithm=serialization.NoEncryption(),
        )
        public_key_bytes = public_key.public_bytes(
            encoding=serialization.Encoding.DER,
            format=serialization.PublicFormat.SubjectPublicKeyInfo,
        )

        return KeyPair(
            private_key=base64.b64encode(private_key_bytes).decode("UTF-8"),
            public_key=base64.b64encode(public_key_bytes).decode("UTF-8"),
        )

    def __init__(self, private_key: str, public_key: str):
        self.private_key = private_key
        self.public_key = public_key

    def get_private_key(self) -> str:
        """Get the private key."""
        return self.private_key

    def get_public_key(self) -> str:
        """Get the public key."""
        return self.public_key