end_to_end_keys.py

# -*- coding: utf-8 -*-
# Copyright 2015, 2016 OpenMarket Ltd
# Copyright 2019 New Vector Ltd
# Copyright 2019 The Matrix.org Foundation C.I.C.
#
# Licensed under the Apache License, Version 2.0 (the "License");
# you may not use this file except in compliance with the License.
# You may obtain a copy of the License at
#
#     http://www.apache.org/licenses/LICENSE-2.0
#
# Unless required by applicable law or agreed to in writing, software
# distributed under the License is distributed on an "AS IS" BASIS,
# WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
# See the License for the specific language governing permissions and
# limitations under the License.
import abc
from typing import TYPE_CHECKING, Dict, Iterable, List, Optional, Tuple

import attr
from canonicaljson import encode_canonical_json

from twisted.enterprise.adbapi import Connection

from synapse.logging.opentracing import log_kv, set_tag, trace
from synapse.storage._base import SQLBaseStore, db_to_json
from synapse.storage.database import make_in_list_sql_clause
from synapse.storage.types import Cursor
from synapse.types import JsonDict
from synapse.util import json_encoder
from synapse.util.caches.descriptors import cached, cachedList
from synapse.util.iterutils import batch_iter

if TYPE_CHECKING:
    from synapse.handlers.e2e_keys import SignatureListItem


@attr.s(slots=True)
class DeviceKeyLookupResult:
    """The type returned by get_e2e_device_keys_and_signatures"""

    display_name = attr.ib(type=Optional[str])

    # the key data from e2e_device_keys_json. Typically includes fields like
    # "algorithm", "keys" (including the curve25519 identity key and the ed25519 signing
    # key) and "signatures" (a map from (user id) to (key id/device_id) to signature.)
    keys = attr.ib(type=Optional[JsonDict])


class EndToEndKeyWorkerStore(SQLBaseStore):
    async def get_e2e_device_keys_for_federation_query(
        self, user_id: str
    ) -> Tuple[int, List[JsonDict]]:
        """Get all devices (with any device keys) for a user

        Returns:
            (stream_id, devices)
        """
        now_stream_id = self.get_device_stream_token()

        devices = await self.get_e2e_device_keys_and_signatures([(user_id, None)])

        if devices:
            user_devices = devices[user_id]
            results = []
            for device_id, device in user_devices.items():
                result = {"device_id": device_id}

                keys = device.keys
                if keys:
                    result["keys"] = keys

                device_display_name = device.display_name
                if device_display_name:
                    result["device_display_name"] = device_display_name

                results.append(result)

            return now_stream_id, results

        return now_stream_id, []

    @trace
    async def get_e2e_device_keys_for_cs_api(
        self, query_list: List[Tuple[str, Optional[str]]]
    ) -> Dict[str, Dict[str, JsonDict]]:
        """Fetch a list of device keys, formatted suitably for the C/S API.
        Args:
            query_list(list): List of pairs of user_ids and device_ids.
        Returns:
            Dict mapping from user-id to dict mapping from device_id to
            key data.  The key data will be a dict in the same format as the
            DeviceKeys type returned by POST /_matrix/client/r0/keys/query.
        """
        set_tag("query_list", query_list)
        if not query_list:
            return {}

        results = await self.get_e2e_device_keys_and_signatures(query_list)

        # Build the result structure, un-jsonify the results, and add the
        # "unsigned" section
        rv = {}
        for user_id, device_keys in results.items():
            rv[user_id] = {}
            for device_id, device_info in device_keys.items():
                r = device_info.keys
                r["unsigned"] = {}
                display_name = device_info.display_name
                if display_name is not None:
                    r["unsigned"]["device_display_name"] = display_name
                rv[user_id][device_id] = r

        return rv

    @trace
    async def get_e2e_device_keys_and_signatures(
        self,
        query_list: List[Tuple[str, Optional[str]]],
        include_all_devices: bool = False,
        include_deleted_devices: bool = False,
    ) -> Dict[str, Dict[str, Optional[DeviceKeyLookupResult]]]:
        """Fetch a list of device keys

        Any cross-signatures made on the keys by the owner of the device are also
        included.

        The cross-signatures are added to the `signatures` field within the `keys`
        object in the response.

        Args:
            query_list: List of pairs of user_ids and device_ids. Device id can be None
                to indicate "all devices for this user"

            include_all_devices: whether to return devices without device keys

            include_deleted_devices: whether to include null entries for
                devices which no longer exist (but were in the query_list).
                This option only takes effect if include_all_devices is true.

        Returns:
            Dict mapping from user-id to dict mapping from device_id to
            key data.
        """
        set_tag("include_all_devices", include_all_devices)
        set_tag("include_deleted_devices", include_deleted_devices)

        result = await self.db_pool.runInteraction(
            "get_e2e_device_keys",
            self._get_e2e_device_keys_txn,
            query_list,
            include_all_devices,
            include_deleted_devices,
        )

        # get the (user_id, device_id) tuples to look up cross-signatures for
        signature_query = (
            (user_id, device_id)
            for user_id, dev in result.items()
            for device_id, d in dev.items()
            if d is not None and d.keys is not None
        )

        for batch in batch_iter(signature_query, 50):
            cross_sigs_result = await self.db_pool.runInteraction(
                "get_e2e_cross_signing_signatures",
                self._get_e2e_cross_signing_signatures_for_devices_txn,
                batch,
            )

            # add each cross-signing signature to the correct device in the result dict.
            for (user_id, key_id, device_id, signature) in cross_sigs_result:
                target_device_result = result[user_id][device_id]
                target_device_signatures = target_device_result.keys.setdefault(
                    "signatures", {}
                )
                signing_user_signatures = target_device_signatures.setdefault(
                    user_id, {}
                )
                signing_user_signatures[key_id] = signature

        log_kv(result)
        return result

    def _get_e2e_device_keys_txn(
        self, txn, query_list, include_all_devices=False, include_deleted_devices=False
    ) -> Dict[str, Dict[str, Optional[DeviceKeyLookupResult]]]:
        """Get information on devices from the database

        The results include the device's keys and self-signatures, but *not* any
        cross-signing signatures which have been added subsequently (for which, see
        get_e2e_device_keys_and_signatures)
        """
        query_clauses = []
        query_params = []

        if include_all_devices is False:
            include_deleted_devices = False

        if include_deleted_devices:
            deleted_devices = set(query_list)

        for (user_id, device_id) in query_list:
            query_clause = "user_id = ?"
            query_params.append(user_id)

            if device_id is not None:
                query_clause += " AND device_id = ?"
                query_params.append(device_id)

            query_clauses.append(query_clause)

        sql = (
            "SELECT user_id, device_id, "
            "    d.display_name, "
            "    k.key_json"
            " FROM devices d"
            "    %s JOIN e2e_device_keys_json k USING (user_id, device_id)"
            " WHERE %s AND NOT d.hidden"
        ) % (
            "LEFT" if include_all_devices else "INNER",
            " OR ".join("(" + q + ")" for q in query_clauses),
        )

        txn.execute(sql, query_params)

        result = {}  # type: Dict[str, Dict[str, Optional[DeviceKeyLookupResult]]]
        for (user_id, device_id, display_name, key_json) in txn:
            if include_deleted_devices:
                deleted_devices.remove((user_id, device_id))
            result.setdefault(user_id, {})[device_id] = DeviceKeyLookupResult(
                display_name, db_to_json(key_json) if key_json else None
            )

        if include_deleted_devices:
            for user_id, device_id in deleted_devices:
                result.setdefault(user_id, {})[device_id] = None

        return result

    def _get_e2e_cross_signing_signatures_for_devices_txn(
        self, txn: Cursor, device_query: Iterable[Tuple[str, str]]
    ) -> List[Tuple[str, str, str, str]]:
        """Get cross-signing signatures for a given list of devices

        Returns signatures made by the owners of the devices.

        Returns: a list of results; each entry in the list is a tuple of
            (user_id, key_id, target_device_id, signature).
        """
        signature_query_clauses = []
        signature_query_params = []

        for (user_id, device_id) in device_query:
            signature_query_clauses.append(
                "target_user_id = ? AND target_device_id = ? AND user_id = ?"
            )
            signature_query_params.extend([user_id, device_id, user_id])

        signature_sql = """
            SELECT user_id, key_id, target_device_id, signature
            FROM e2e_cross_signing_signatures WHERE %s
            """ % (
            " OR ".join("(" + q + ")" for q in signature_query_clauses)
        )

        txn.execute(signature_sql, signature_query_params)
        return txn.fetchall()

    async def get_e2e_one_time_keys(
        self, user_id: str, device_id: str, key_ids: List[str]
    ) -> Dict[Tuple[str, str], str]:
        """Retrieve a number of one-time keys for a user

        Args:
            user_id(str): id of user to get keys for
            device_id(str): id of device to get keys for
            key_ids(list[str]): list of key ids (excluding algorithm) to
                retrieve

        Returns:
            A map from (algorithm, key_id) to json string for key
        """

        rows = await self.db_pool.simple_select_many_batch(
            table="e2e_one_time_keys_json",
            column="key_id",
            iterable=key_ids,
            retcols=("algorithm", "key_id", "key_json"),
            keyvalues={"user_id": user_id, "device_id": device_id},
            desc="add_e2e_one_time_keys_check",
        )
        result = {(row["algorithm"], row["key_id"]): row["key_json"] for row in rows}
        log_kv({"message": "Fetched one time keys for user", "one_time_keys": result})
        return result

    async def add_e2e_one_time_keys(
        self,
        user_id: str,
        device_id: str,
        time_now: int,
        new_keys: Iterable[Tuple[str, str, str]],
    ) -> None:
        """Insert some new one time keys for a device. Errors if any of the
        keys already exist.

        Args:
            user_id: id of user to get keys for
            device_id: id of device to get keys for
            time_now: insertion time to record (ms since epoch)
            new_keys: keys to add - each a tuple of (algorithm, key_id, key json)
        """

        def _add_e2e_one_time_keys(txn):
            set_tag("user_id", user_id)
            set_tag("device_id", device_id)
            set_tag("new_keys", new_keys)
            # We are protected from race between lookup and insertion due to
            # a unique constraint. If there is a race of two calls to
            # `add_e2e_one_time_keys` then they'll conflict and we will only
            # insert one set.
            self.db_pool.simple_insert_many_txn(
                txn,
                table="e2e_one_time_keys_json",
                values=[
                    {
                        "user_id": user_id,
                        "device_id": device_id,
                        "algorithm": algorithm,
                        "key_id": key_id,
                        "ts_added_ms": time_now,
                        "key_json": json_bytes,
                    }
                    for algorithm, key_id, json_bytes in new_keys
                ],
            )
            self._invalidate_cache_and_stream(
                txn, self.count_e2e_one_time_keys, (user_id, device_id)
            )

        await self.db_pool.runInteraction(
            "add_e2e_one_time_keys_insert", _add_e2e_one_time_keys
        )

    @cached(max_entries=10000)
    async def count_e2e_one_time_keys(
        self, user_id: str, device_id: str
    ) -> Dict[str, int]:
        """ Count the number of one time keys the server has for a device
        Returns:
            A mapping from algorithm to number of keys for that algorithm.
        """

        def _count_e2e_one_time_keys(txn):
            sql = (
                "SELECT algorithm, COUNT(key_id) FROM e2e_one_time_keys_json"
                " WHERE user_id = ? AND device_id = ?"
                " GROUP BY algorithm"
            )
            txn.execute(sql, (user_id, device_id))
            result = {}
            for algorithm, key_count in txn:
                result[algorithm] = key_count
            return result

        return await self.db_pool.runInteraction(
            "count_e2e_one_time_keys", _count_e2e_one_time_keys
        )

    async def get_e2e_cross_signing_key(
        self, user_id: str, key_type: str, from_user_id: Optional[str] = None
    ) -> Optional[dict]:
        """Returns a user's cross-signing key.

        Args:
            user_id: the user whose key is being requested
            key_type: the type of key that is being requested: either 'master'
                for a master key, 'self_signing' for a self-signing key, or
                'user_signing' for a user-signing key
            from_user_id: if specified, signatures made by this user on
                the self-signing key will be included in the result

        Returns:
            dict of the key data or None if not found
        """
        res = await self.get_e2e_cross_signing_keys_bulk([user_id], from_user_id)
        user_keys = res.get(user_id)
        if not user_keys:
            return None
        return user_keys.get(key_type)

    @cached(num_args=1)
    def _get_bare_e2e_cross_signing_keys(self, user_id):
        """Dummy function.  Only used to make a cache for
        _get_bare_e2e_cross_signing_keys_bulk.
        """
        raise NotImplementedError()

    @cachedList(
        cached_method_name="_get_bare_e2e_cross_signing_keys",
        list_name="user_ids",
        num_args=1,
    )
    async def _get_bare_e2e_cross_signing_keys_bulk(
        self, user_ids: List[str]
    ) -> Dict[str, Dict[str, dict]]:
        """Returns the cross-signing keys for a set of users.  The output of this
        function should be passed to _get_e2e_cross_signing_signatures_txn if
        the signatures for the calling user need to be fetched.

        Args:
            user_ids: the users whose keys are being requested

        Returns:
            A mapping from user ID to key type to key data. If a user's cross-signing
            keys were not found, either their user ID will not be in the dict, or
            their user ID will map to None.

        """
        return await self.db_pool.runInteraction(
            "get_bare_e2e_cross_signing_keys_bulk",
            self._get_bare_e2e_cross_signing_keys_bulk_txn,
            user_ids,
        )

    def _get_bare_e2e_cross_signing_keys_bulk_txn(
        self, txn: Connection, user_ids: List[str],
    ) -> Dict[str, Dict[str, dict]]:
        """Returns the cross-signing keys for a set of users.  The output of this
        function should be passed to _get_e2e_cross_signing_signatures_txn if
        the signatures for the calling user need to be fetched.

        Args:
            txn (twisted.enterprise.adbapi.Connection): db connection
            user_ids (list[str]): the users whose keys are being requested

        Returns:
            dict[str, dict[str, dict]]: mapping from user ID to key type to key
                data.  If a user's cross-signing keys were not found, their user
                ID will not be in the dict.

        """
        result = {}

        for user_chunk in batch_iter(user_ids, 100):
            clause, params = make_in_list_sql_clause(
                txn.database_engine, "k.user_id", user_chunk
            )
            sql = (
                """
                SELECT k.user_id, k.keytype, k.keydata, k.stream_id
                  FROM e2e_cross_signing_keys k
                  INNER JOIN (SELECT user_id, keytype, MAX(stream_id) AS stream_id
                                FROM e2e_cross_signing_keys
                               GROUP BY user_id, keytype) s
                 USING (user_id, stream_id, keytype)
                 WHERE
            """
                + clause
            )

            txn.execute(sql, params)
            rows = self.db_pool.cursor_to_dict(txn)

            for row in rows:
                user_id = row["user_id"]
                key_type = row["keytype"]
                key = db_to_json(row["keydata"])
                user_info = result.setdefault(user_id, {})
                user_info[key_type] = key

        return result

    def _get_e2e_cross_signing_signatures_txn(
        self, txn: Connection, keys: Dict[str, Dict[str, dict]], from_user_id: str,
    ) -> Dict[str, Dict[str, dict]]:
        """Returns the cross-signing signatures made by a user on a set of keys.

        Args:
            txn (twisted.enterprise.adbapi.Connection): db connection
            keys (dict[str, dict[str, dict]]): a map of user ID to key type to
                key data.  This dict will be modified to add signatures.
            from_user_id (str): fetch the signatures made by this user

        Returns:
            dict[str, dict[str, dict]]: mapping from user ID to key type to key
                data.  The return value will be the same as the keys argument,
                with the modifications included.
        """

        # find out what cross-signing keys (a.k.a. devices) we need to get
        # signatures for.  This is a map of (user_id, device_id) to key type
        # (device_id is the key's public part).
        devices = {}

        for user_id, user_info in keys.items():
            if user_info is None:
                continue
            for key_type, key in user_info.items():
                device_id = None
                for k in key["keys"].values():
                    device_id = k
                devices[(user_id, device_id)] = key_type

        for batch in batch_iter(devices.keys(), size=100):
            sql = """
                SELECT target_user_id, target_device_id, key_id, signature
                  FROM e2e_cross_signing_signatures
                 WHERE user_id = ?
                   AND (%s)
            """ % (
                " OR ".join(
                    "(target_user_id = ? AND target_device_id = ?)" for _ in batch
                )
            )
            query_params = [from_user_id]
            for item in batch:
                # item is a (user_id, device_id) tuple
                query_params.extend(item)

            txn.execute(sql, query_params)
            rows = self.db_pool.cursor_to_dict(txn)

            # and add the signatures to the appropriate keys
            for row in rows:
                key_id = row["key_id"]
                target_user_id = row["target_user_id"]
                target_device_id = row["target_device_id"]
                key_type = devices[(target_user_id, target_device_id)]
                # We need to copy everything, because the result may have come
                # from the cache.  dict.copy only does a shallow copy, so we
                # need to recursively copy the dicts that will be modified.
                user_info = keys[target_user_id] = keys[target_user_id].copy()
                target_user_key = user_info[key_type] = user_info[key_type].copy()
                if "signatures" in target_user_key:
                    signatures = target_user_key["signatures"] = target_user_key[
                        "signatures"
                    ].copy()
                    if from_user_id in signatures:
                        user_sigs = signatures[from_user_id] = signatures[from_user_id]
                        user_sigs[key_id] = row["signature"]
                    else:
                        signatures[from_user_id] = {key_id: row["signature"]}
                else:
                    target_user_key["signatures"] = {
                        from_user_id: {key_id: row["signature"]}
                    }

        return keys

    async def get_e2e_cross_signing_keys_bulk(
        self, user_ids: List[str], from_user_id: Optional[str] = None
    ) -> Dict[str, Dict[str, dict]]:
        """Returns the cross-signing keys for a set of users.

        Args:
            user_ids: the users whose keys are being requested
            from_user_id: if specified, signatures made by this user on
                the self-signing keys will be included in the result

        Returns:
            A map of user ID to key type to key data.  If a user's cross-signing
            keys were not found, either their user ID will not be in the dict,
            or their user ID will map to None.
        """

        result = await self._get_bare_e2e_cross_signing_keys_bulk(user_ids)

        if from_user_id:
            result = await self.db_pool.runInteraction(
                "get_e2e_cross_signing_signatures",
                self._get_e2e_cross_signing_signatures_txn,
                result,
                from_user_id,
            )

        return result

    async def get_all_user_signature_changes_for_remotes(
        self, instance_name: str, last_id: int, current_id: int, limit: int
    ) -> Tuple[List[Tuple[int, tuple]], int, bool]:
        """Get updates for groups replication stream.

        Note that the user signature stream represents when a user signs their
        device with their user-signing key, which is not published to other
        users or servers, so no `destination` is needed in the returned
        list. However, this is needed to poke workers.

        Args:
            instance_name: The writer we want to fetch updates from. Unused
                here since there is only ever one writer.
            last_id: The token to fetch updates from. Exclusive.
            current_id: The token to fetch updates up to. Inclusive.
            limit: The requested limit for the number of rows to return. The
                function may return more or fewer rows.

        Returns:
            A tuple consisting of: the updates, a token to use to fetch
            subsequent updates, and whether we returned fewer rows than exists
            between the requested tokens due to the limit.

            The token returned can be used in a subsequent call to this
            function to get further updatees.

            The updates are a list of 2-tuples of stream ID and the row data
        """

        if last_id == current_id:
            return [], current_id, False

        def _get_all_user_signature_changes_for_remotes_txn(txn):
            sql = """
                SELECT stream_id, from_user_id AS user_id
                FROM user_signature_stream
                WHERE ? < stream_id AND stream_id <= ?
                ORDER BY stream_id ASC
                LIMIT ?
            """
            txn.execute(sql, (last_id, current_id, limit))

            updates = [(row[0], (row[1:])) for row in txn]

            limited = False
            upto_token = current_id
            if len(updates) >= limit:
                upto_token = updates[-1][0]
                limited = True

            return updates, upto_token, limited

        return await self.db_pool.runInteraction(
            "get_all_user_signature_changes_for_remotes",
            _get_all_user_signature_changes_for_remotes_txn,
        )

    @abc.abstractmethod
    def get_device_stream_token(self) -> int:
        """Get the current stream id from the _device_list_id_gen"""
        ...


class EndToEndKeyStore(EndToEndKeyWorkerStore, SQLBaseStore):
    async def set_e2e_device_keys(
        self, user_id: str, device_id: str, time_now: int, device_keys: JsonDict
    ) -> bool:
        """Stores device keys for a device. Returns whether there was a change
        or the keys were already in the database.
        """

        def _set_e2e_device_keys_txn(txn):
            set_tag("user_id", user_id)
            set_tag("device_id", device_id)
            set_tag("time_now", time_now)
            set_tag("device_keys", device_keys)

            old_key_json = self.db_pool.simple_select_one_onecol_txn(
                txn,
                table="e2e_device_keys_json",
                keyvalues={"user_id": user_id, "device_id": device_id},
                retcol="key_json",
                allow_none=True,
            )

            # In py3 we need old_key_json to match new_key_json type. The DB
            # returns unicode while encode_canonical_json returns bytes.
            new_key_json = encode_canonical_json(device_keys).decode("utf-8")

            if old_key_json == new_key_json:
                log_kv({"Message": "Device key already stored."})
                return False

            self.db_pool.simple_upsert_txn(
                txn,
                table="e2e_device_keys_json",
                keyvalues={"user_id": user_id, "device_id": device_id},
                values={"ts_added_ms": time_now, "key_json": new_key_json},
            )
            log_kv({"message": "Device keys stored."})
            return True

        return await self.db_pool.runInteraction(
            "set_e2e_device_keys", _set_e2e_device_keys_txn
        )

    async def claim_e2e_one_time_keys(
        self, query_list: Iterable[Tuple[str, str, str]]
    ) -> Dict[str, Dict[str, Dict[str, bytes]]]:
        """Take a list of one time keys out of the database.

        Args:
            query_list: An iterable of tuples of (user ID, device ID, algorithm).

        Returns:
            A map of user ID -> a map device ID -> a map of key ID -> JSON bytes.
        """

        @trace
        def _claim_e2e_one_time_keys(txn):
            sql = (
                "SELECT key_id, key_json FROM e2e_one_time_keys_json"
                " WHERE user_id = ? AND device_id = ? AND algorithm = ?"
                " LIMIT 1"
            )
            result = {}
            delete = []
            for user_id, device_id, algorithm in query_list:
                user_result = result.setdefault(user_id, {})
                device_result = user_result.setdefault(device_id, {})
                txn.execute(sql, (user_id, device_id, algorithm))
                for key_id, key_json in txn:
                    device_result[algorithm + ":" + key_id] = key_json
                    delete.append((user_id, device_id, algorithm, key_id))
            sql = (
                "DELETE FROM e2e_one_time_keys_json"
                " WHERE user_id = ? AND device_id = ? AND algorithm = ?"
                " AND key_id = ?"
            )
            for user_id, device_id, algorithm, key_id in delete:
                log_kv(
                    {
                        "message": "Executing claim e2e_one_time_keys transaction on database."
                    }
                )
                txn.execute(sql, (user_id, device_id, algorithm, key_id))
                log_kv({"message": "finished executing and invalidating cache"})
                self._invalidate_cache_and_stream(
                    txn, self.count_e2e_one_time_keys, (user_id, device_id)
                )
            return result

        return await self.db_pool.runInteraction(
            "claim_e2e_one_time_keys", _claim_e2e_one_time_keys
        )

    async def delete_e2e_keys_by_device(self, user_id: str, device_id: str) -> None:
        def delete_e2e_keys_by_device_txn(txn):
            log_kv(
                {
                    "message": "Deleting keys for device",
                    "device_id": device_id,
                    "user_id": user_id,
                }
            )
            self.db_pool.simple_delete_txn(
                txn,
                table="e2e_device_keys_json",
                keyvalues={"user_id": user_id, "device_id": device_id},
            )
            self.db_pool.simple_delete_txn(
                txn,
                table="e2e_one_time_keys_json",
                keyvalues={"user_id": user_id, "device_id": device_id},
            )
            self._invalidate_cache_and_stream(
                txn, self.count_e2e_one_time_keys, (user_id, device_id)
            )

        await self.db_pool.runInteraction(
            "delete_e2e_keys_by_device", delete_e2e_keys_by_device_txn
        )

    def _set_e2e_cross_signing_key_txn(self, txn, user_id, key_type, key, stream_id):
        """Set a user's cross-signing key.

        Args:
            txn (twisted.enterprise.adbapi.Connection): db connection
            user_id (str): the user to set the signing key for
            key_type (str): the type of key that is being set: either 'master'
                for a master key, 'self_signing' for a self-signing key, or
                'user_signing' for a user-signing key
            key (dict): the key data
            stream_id (int)
        """
        # the 'key' dict will look something like:
        # {
        #   "user_id": "@alice:example.com",
        #   "usage": ["self_signing"],
        #   "keys": {
        #     "ed25519:base64+self+signing+public+key": "base64+self+signing+public+key",
        #   },
        #   "signatures": {
        #     "@alice:example.com": {
        #       "ed25519:base64+master+public+key": "base64+signature"
        #     }
        #   }
        # }
        # The "keys" property must only have one entry, which will be the public
        # key, so we just grab the first value in there
        pubkey = next(iter(key["keys"].values()))

        # The cross-signing keys need to occupy the same namespace as devices,
        # since signatures are identified by device ID.  So add an entry to the
        # device table to make sure that we don't have a collision with device
        # IDs.
        # We only need to do this for local users, since remote servers should be
        # responsible for checking this for their own users.
        if self.hs.is_mine_id(user_id):
            self.db_pool.simple_insert_txn(
                txn,
                "devices",
                values={
                    "user_id": user_id,
                    "device_id": pubkey,
                    "display_name": key_type + " signing key",
                    "hidden": True,
                },
            )

        # and finally, store the key itself
        self.db_pool.simple_insert_txn(
            txn,
            "e2e_cross_signing_keys",
            values={
                "user_id": user_id,
                "keytype": key_type,
                "keydata": json_encoder.encode(key),
                "stream_id": stream_id,
            },
        )

        self._invalidate_cache_and_stream(
            txn, self._get_bare_e2e_cross_signing_keys, (user_id,)
        )

    async def set_e2e_cross_signing_key(self, user_id, key_type, key):
        """Set a user's cross-signing key.

        Args:
            user_id (str): the user to set the user-signing key for
            key_type (str): the type of cross-signing key to set
            key (dict): the key data
        """

        with await self._cross_signing_id_gen.get_next() as stream_id:
            return await self.db_pool.runInteraction(
                "add_e2e_cross_signing_key",
                self._set_e2e_cross_signing_key_txn,
                user_id,
                key_type,
                key,
                stream_id,
            )

    async def store_e2e_cross_signing_signatures(
        self, user_id: str, signatures: "Iterable[SignatureListItem]"
    ) -> None:
        """Stores cross-signing signatures.

        Args:
            user_id: the user who made the signatures
            signatures: signatures to add
        """
        await self.db_pool.simple_insert_many(
            "e2e_cross_signing_signatures",
            [
                {
                    "user_id": user_id,
                    "key_id": item.signing_key_id,
                    "target_user_id": item.target_user_id,
                    "target_device_id": item.target_device_id,
                    "signature": item.signature,
                }
                for item in signatures
            ],
            "add_e2e_signing_key",
        )