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Merge pull request #4493 from matrix-org/erikj/refactor_event_signing
Refactor event signing to work on dicts
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changelog.d/4493.misc
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changelog.d/4493.misc
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Add infrastructure to support different event formats
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@ -23,14 +23,14 @@ from signedjson.sign import sign_json
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from unpaddedbase64 import decode_base64, encode_base64
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from synapse.api.errors import Codes, SynapseError
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from synapse.events.utils import prune_event
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from synapse.events.utils import prune_event, prune_event_dict
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logger = logging.getLogger(__name__)
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def check_event_content_hash(event, hash_algorithm=hashlib.sha256):
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"""Check whether the hash for this PDU matches the contents"""
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name, expected_hash = compute_content_hash(event, hash_algorithm)
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name, expected_hash = compute_content_hash(event.get_pdu_json(), hash_algorithm)
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logger.debug("Expecting hash: %s", encode_base64(expected_hash))
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# some malformed events lack a 'hashes'. Protect against it being missing
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@ -59,35 +59,70 @@ def check_event_content_hash(event, hash_algorithm=hashlib.sha256):
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return message_hash_bytes == expected_hash
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def compute_content_hash(event, hash_algorithm):
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event_json = event.get_pdu_json()
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event_json.pop("age_ts", None)
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event_json.pop("unsigned", None)
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event_json.pop("signatures", None)
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event_json.pop("hashes", None)
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event_json.pop("outlier", None)
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event_json.pop("destinations", None)
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def compute_content_hash(event_dict, hash_algorithm):
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"""Compute the content hash of an event, which is the hash of the
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unredacted event.
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event_json_bytes = encode_canonical_json(event_json)
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Args:
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event_dict (dict): The unredacted event as a dict
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hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
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to hash the event
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Returns:
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tuple[str, bytes]: A tuple of the name of hash and the hash as raw
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bytes.
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"""
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event_dict = dict(event_dict)
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event_dict.pop("age_ts", None)
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event_dict.pop("unsigned", None)
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event_dict.pop("signatures", None)
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event_dict.pop("hashes", None)
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event_dict.pop("outlier", None)
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event_dict.pop("destinations", None)
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event_json_bytes = encode_canonical_json(event_dict)
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hashed = hash_algorithm(event_json_bytes)
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return (hashed.name, hashed.digest())
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def compute_event_reference_hash(event, hash_algorithm=hashlib.sha256):
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"""Computes the event reference hash. This is the hash of the redacted
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event.
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Args:
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event (FrozenEvent)
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hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
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to hash the event
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Returns:
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tuple[str, bytes]: A tuple of the name of hash and the hash as raw
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bytes.
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"""
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tmp_event = prune_event(event)
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event_json = tmp_event.get_pdu_json()
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event_json.pop("signatures", None)
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event_json.pop("age_ts", None)
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event_json.pop("unsigned", None)
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event_json_bytes = encode_canonical_json(event_json)
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event_dict = tmp_event.get_pdu_json()
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event_dict.pop("signatures", None)
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event_dict.pop("age_ts", None)
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event_dict.pop("unsigned", None)
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event_json_bytes = encode_canonical_json(event_dict)
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hashed = hash_algorithm(event_json_bytes)
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return (hashed.name, hashed.digest())
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def compute_event_signature(event, signature_name, signing_key):
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tmp_event = prune_event(event)
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redact_json = tmp_event.get_pdu_json()
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def compute_event_signature(event_dict, signature_name, signing_key):
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"""Compute the signature of the event for the given name and key.
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Args:
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event_dict (dict): The event as a dict
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signature_name (str): The name of the entity signing the event
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(typically the server's hostname).
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signing_key (syutil.crypto.SigningKey): The key to sign with
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Returns:
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dict[str, dict[str, str]]: Returns a dictionary in the same format of
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an event's signatures field.
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"""
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redact_json = prune_event_dict(event_dict)
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redact_json.pop("age_ts", None)
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redact_json.pop("unsigned", None)
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logger.debug("Signing event: %s", encode_canonical_json(redact_json))
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@ -98,23 +133,27 @@ def compute_event_signature(event, signature_name, signing_key):
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def add_hashes_and_signatures(event, signature_name, signing_key,
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hash_algorithm=hashlib.sha256):
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# if hasattr(event, "old_state_events"):
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# state_json_bytes = encode_canonical_json(
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# [e.event_id for e in event.old_state_events.values()]
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# )
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# hashed = hash_algorithm(state_json_bytes)
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# event.state_hash = {
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# hashed.name: encode_base64(hashed.digest())
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# }
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"""Add content hash and sign the event
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name, digest = compute_content_hash(event, hash_algorithm=hash_algorithm)
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Args:
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event_dict (EventBuilder): The event to add hashes to and sign
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signature_name (str): The name of the entity signing the event
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(typically the server's hostname).
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signing_key (syutil.crypto.SigningKey): The key to sign with
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hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
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to hash the event
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"""
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name, digest = compute_content_hash(
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event.get_pdu_json(), hash_algorithm=hash_algorithm,
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)
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if not hasattr(event, "hashes"):
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event.hashes = {}
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event.hashes[name] = encode_base64(digest)
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event.signatures = compute_event_signature(
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event,
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event.get_pdu_json(),
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signature_name=signature_name,
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signing_key=signing_key,
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)
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@ -38,8 +38,31 @@ def prune_event(event):
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This is used when we "redact" an event. We want to remove all fields that
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the user has specified, but we do want to keep necessary information like
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type, state_key etc.
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Args:
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event (FrozenEvent)
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Returns:
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FrozenEvent
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"""
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pruned_event_dict = prune_event_dict(event.get_dict())
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from . import event_type_from_format_version
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return event_type_from_format_version(event.format_version)(
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pruned_event_dict, event.internal_metadata.get_dict()
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)
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def prune_event_dict(event_dict):
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"""Redacts the event_dict in the same way as `prune_event`, except it
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operates on dicts rather than event objects
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Args:
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event_dict (dict)
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Returns:
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dict: A copy of the pruned event dict
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"""
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event_type = event.type
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allowed_keys = [
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"event_id",
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@ -59,13 +82,13 @@ def prune_event(event):
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"membership",
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]
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event_dict = event.get_dict()
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event_type = event_dict["type"]
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new_content = {}
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def add_fields(*fields):
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for field in fields:
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if field in event.content:
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if field in event_dict["content"]:
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new_content[field] = event_dict["content"][field]
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if event_type == EventTypes.Member:
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@ -98,17 +121,17 @@ def prune_event(event):
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allowed_fields["content"] = new_content
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allowed_fields["unsigned"] = {}
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unsigned = {}
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allowed_fields["unsigned"] = unsigned
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if "age_ts" in event.unsigned:
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allowed_fields["unsigned"]["age_ts"] = event.unsigned["age_ts"]
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if "replaces_state" in event.unsigned:
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allowed_fields["unsigned"]["replaces_state"] = event.unsigned["replaces_state"]
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event_unsigned = event_dict.get("unsigned", {})
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return type(event)(
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allowed_fields,
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internal_metadata_dict=event.internal_metadata.get_dict()
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)
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if "age_ts" in event_unsigned:
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unsigned["age_ts"] = event_unsigned["age_ts"]
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if "replaces_state" in event_unsigned:
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unsigned["replaces_state"] = event_unsigned["replaces_state"]
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return allowed_fields
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def _copy_field(src, dst, field):
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