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- #
- # Copyright 2014-2016 OpenMarket Ltd
- # Copyright 2020 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 collections.abc
- import hashlib
- import logging
- from typing import Any, Callable, Dict, Tuple
- from canonicaljson import encode_canonical_json
- from signedjson.sign import sign_json
- from signedjson.types import SigningKey
- from unpaddedbase64 import decode_base64, encode_base64
- from synapse.api.errors import Codes, SynapseError
- from synapse.api.room_versions import RoomVersion
- from synapse.events import EventBase
- from synapse.events.utils import prune_event, prune_event_dict
- from synapse.types import JsonDict
- logger = logging.getLogger(__name__)
- Hasher = Callable[[bytes], "hashlib._Hash"]
- def check_event_content_hash(
- event: EventBase, hash_algorithm: Hasher = hashlib.sha256
- ) -> bool:
- """Check whether the hash for this PDU matches the contents"""
- name, expected_hash = compute_content_hash(event.get_pdu_json(), hash_algorithm)
- logger.debug(
- "Verifying content hash on %s (expecting: %s)",
- event.event_id,
- encode_base64(expected_hash),
- )
- # some malformed events lack a 'hashes'. Protect against it being missing
- # or a weird type by basically treating it the same as an unhashed event.
- hashes = event.get("hashes")
- # nb it might be a frozendict or a dict
- if not isinstance(hashes, collections.abc.Mapping):
- raise SynapseError(
- 400, "Malformed 'hashes': %s" % (type(hashes),), Codes.UNAUTHORIZED
- )
- if name not in hashes:
- raise SynapseError(
- 400,
- "Algorithm %s not in hashes %s" % (name, list(hashes)),
- Codes.UNAUTHORIZED,
- )
- message_hash_base64 = hashes[name]
- try:
- message_hash_bytes = decode_base64(message_hash_base64)
- except Exception:
- raise SynapseError(
- 400, "Invalid base64: %s" % (message_hash_base64,), Codes.UNAUTHORIZED
- )
- return message_hash_bytes == expected_hash
- def compute_content_hash(
- event_dict: Dict[str, Any], hash_algorithm: Hasher
- ) -> Tuple[str, bytes]:
- """Compute the content hash of an event, which is the hash of the
- unredacted event.
- Args:
- event_dict: The unredacted event as a dict
- hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
- to hash the event
- Returns:
- A tuple of the name of hash and the hash as raw bytes.
- """
- event_dict = dict(event_dict)
- event_dict.pop("age_ts", None)
- event_dict.pop("unsigned", None)
- event_dict.pop("signatures", None)
- event_dict.pop("hashes", None)
- event_dict.pop("outlier", None)
- event_dict.pop("destinations", None)
- event_json_bytes = encode_canonical_json(event_dict)
- hashed = hash_algorithm(event_json_bytes)
- return hashed.name, hashed.digest()
- def compute_event_reference_hash(
- event, hash_algorithm: Hasher = hashlib.sha256
- ) -> Tuple[str, bytes]:
- """Computes the event reference hash. This is the hash of the redacted
- event.
- Args:
- event
- hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
- to hash the event
- Returns:
- A tuple of the name of hash and the hash as raw bytes.
- """
- tmp_event = prune_event(event)
- event_dict = tmp_event.get_pdu_json()
- event_dict.pop("signatures", None)
- event_dict.pop("age_ts", None)
- event_dict.pop("unsigned", None)
- event_json_bytes = encode_canonical_json(event_dict)
- hashed = hash_algorithm(event_json_bytes)
- return hashed.name, hashed.digest()
- def compute_event_signature(
- room_version: RoomVersion,
- event_dict: JsonDict,
- signature_name: str,
- signing_key: SigningKey,
- ) -> Dict[str, Dict[str, str]]:
- """Compute the signature of the event for the given name and key.
- Args:
- room_version: the version of the room that this event is in.
- (the room version determines the redaction algorithm and hence the
- json to be signed)
- event_dict: The event as a dict
- signature_name: The name of the entity signing the event
- (typically the server's hostname).
- signing_key: The key to sign with
- Returns:
- a dictionary in the same format of an event's signatures field.
- """
- redact_json = prune_event_dict(room_version, event_dict)
- redact_json.pop("age_ts", None)
- redact_json.pop("unsigned", None)
- if logger.isEnabledFor(logging.DEBUG):
- logger.debug("Signing event: %s", encode_canonical_json(redact_json))
- redact_json = sign_json(redact_json, signature_name, signing_key)
- if logger.isEnabledFor(logging.DEBUG):
- logger.debug("Signed event: %s", encode_canonical_json(redact_json))
- return redact_json["signatures"]
- def add_hashes_and_signatures(
- room_version: RoomVersion,
- event_dict: JsonDict,
- signature_name: str,
- signing_key: SigningKey,
- ) -> None:
- """Add content hash and sign the event
- Args:
- room_version: the version of the room this event is in
- event_dict: The event to add hashes to and sign
- signature_name: The name of the entity signing the event
- (typically the server's hostname).
- signing_key: The key to sign with
- """
- name, digest = compute_content_hash(event_dict, hash_algorithm=hashlib.sha256)
- event_dict.setdefault("hashes", {})[name] = encode_base64(digest)
- event_dict["signatures"] = compute_event_signature(
- room_version, event_dict, signature_name=signature_name, signing_key=signing_key
- )
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