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#
# This file is licensed under the Affero General Public License (AGPL) version 3.
#
# Copyright (C) 2023 New Vector, Ltd
#
# This program is free software: you can redistribute it and/or modify
# it under the terms of the GNU Affero General Public License as
# published by the Free Software Foundation, either version 3 of the
# License, or (at your option) any later version.
#
# See the GNU Affero General Public License for more details:
# <https://www.gnu.org/licenses/agpl-3.0.html>.
#
# Originally licensed under the Apache License, Version 2.0:
# <http://www.apache.org/licenses/LICENSE-2.0>.
#
# [This file includes modifications made by New Vector Limited]
#
#
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.logging.opentracing import trace
from synapse.types import JsonDict
logger = logging.getLogger(__name__)
Hasher = Callable[[bytes], "hashlib._Hash"]
@trace
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 immutabledict 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: EventBase, 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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