Merge pull request #4493 from matrix-org/erikj/refactor_event_signing

Refactor event signing to work on dicts
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Erik Johnston 2019-01-29 09:52:54 +00:00 committed by GitHub
commit 17709f8f9c
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3 changed files with 104 additions and 41 deletions

1
changelog.d/4493.misc Normal file
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@ -0,0 +1 @@
Add infrastructure to support different event formats

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@ -23,14 +23,14 @@ from signedjson.sign import sign_json
from unpaddedbase64 import decode_base64, encode_base64
from synapse.api.errors import Codes, SynapseError
from synapse.events.utils import prune_event
from synapse.events.utils import prune_event, prune_event_dict
logger = logging.getLogger(__name__)
def check_event_content_hash(event, hash_algorithm=hashlib.sha256):
"""Check whether the hash for this PDU matches the contents"""
name, expected_hash = compute_content_hash(event, hash_algorithm)
name, expected_hash = compute_content_hash(event.get_pdu_json(), hash_algorithm)
logger.debug("Expecting hash: %s", encode_base64(expected_hash))
# some malformed events lack a 'hashes'. Protect against it being missing
@ -59,35 +59,70 @@ def check_event_content_hash(event, hash_algorithm=hashlib.sha256):
return message_hash_bytes == expected_hash
def compute_content_hash(event, hash_algorithm):
event_json = event.get_pdu_json()
event_json.pop("age_ts", None)
event_json.pop("unsigned", None)
event_json.pop("signatures", None)
event_json.pop("hashes", None)
event_json.pop("outlier", None)
event_json.pop("destinations", None)
def compute_content_hash(event_dict, hash_algorithm):
"""Compute the content hash of an event, which is the hash of the
unredacted event.
event_json_bytes = encode_canonical_json(event_json)
Args:
event_dict (dict): The unredacted event as a dict
hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
to hash the event
Returns:
tuple[str, bytes]: 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=hashlib.sha256):
"""Computes the event reference hash. This is the hash of the redacted
event.
Args:
event (FrozenEvent)
hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
to hash the event
Returns:
tuple[str, bytes]: A tuple of the name of hash and the hash as raw
bytes.
"""
tmp_event = prune_event(event)
event_json = tmp_event.get_pdu_json()
event_json.pop("signatures", None)
event_json.pop("age_ts", None)
event_json.pop("unsigned", None)
event_json_bytes = encode_canonical_json(event_json)
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(event, signature_name, signing_key):
tmp_event = prune_event(event)
redact_json = tmp_event.get_pdu_json()
def compute_event_signature(event_dict, signature_name, signing_key):
"""Compute the signature of the event for the given name and key.
Args:
event_dict (dict): The event as a dict
signature_name (str): The name of the entity signing the event
(typically the server's hostname).
signing_key (syutil.crypto.SigningKey): The key to sign with
Returns:
dict[str, dict[str, str]]: Returns a dictionary in the same format of
an event's signatures field.
"""
redact_json = prune_event_dict(event_dict)
redact_json.pop("age_ts", None)
redact_json.pop("unsigned", None)
logger.debug("Signing event: %s", encode_canonical_json(redact_json))
@ -98,23 +133,27 @@ def compute_event_signature(event, signature_name, signing_key):
def add_hashes_and_signatures(event, signature_name, signing_key,
hash_algorithm=hashlib.sha256):
# if hasattr(event, "old_state_events"):
# state_json_bytes = encode_canonical_json(
# [e.event_id for e in event.old_state_events.values()]
# )
# hashed = hash_algorithm(state_json_bytes)
# event.state_hash = {
# hashed.name: encode_base64(hashed.digest())
# }
"""Add content hash and sign the event
name, digest = compute_content_hash(event, hash_algorithm=hash_algorithm)
Args:
event_dict (EventBuilder): The event to add hashes to and sign
signature_name (str): The name of the entity signing the event
(typically the server's hostname).
signing_key (syutil.crypto.SigningKey): The key to sign with
hash_algorithm: A hasher from `hashlib`, e.g. hashlib.sha256, to use
to hash the event
"""
name, digest = compute_content_hash(
event.get_pdu_json(), hash_algorithm=hash_algorithm,
)
if not hasattr(event, "hashes"):
event.hashes = {}
event.hashes[name] = encode_base64(digest)
event.signatures = compute_event_signature(
event,
event.get_pdu_json(),
signature_name=signature_name,
signing_key=signing_key,
)

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@ -38,8 +38,31 @@ def prune_event(event):
This is used when we "redact" an event. We want to remove all fields that
the user has specified, but we do want to keep necessary information like
type, state_key etc.
Args:
event (FrozenEvent)
Returns:
FrozenEvent
"""
pruned_event_dict = prune_event_dict(event.get_dict())
from . import event_type_from_format_version
return event_type_from_format_version(event.format_version)(
pruned_event_dict, event.internal_metadata.get_dict()
)
def prune_event_dict(event_dict):
"""Redacts the event_dict in the same way as `prune_event`, except it
operates on dicts rather than event objects
Args:
event_dict (dict)
Returns:
dict: A copy of the pruned event dict
"""
event_type = event.type
allowed_keys = [
"event_id",
@ -59,13 +82,13 @@ def prune_event(event):
"membership",
]
event_dict = event.get_dict()
event_type = event_dict["type"]
new_content = {}
def add_fields(*fields):
for field in fields:
if field in event.content:
if field in event_dict["content"]:
new_content[field] = event_dict["content"][field]
if event_type == EventTypes.Member:
@ -98,17 +121,17 @@ def prune_event(event):
allowed_fields["content"] = new_content
allowed_fields["unsigned"] = {}
unsigned = {}
allowed_fields["unsigned"] = unsigned
if "age_ts" in event.unsigned:
allowed_fields["unsigned"]["age_ts"] = event.unsigned["age_ts"]
if "replaces_state" in event.unsigned:
allowed_fields["unsigned"]["replaces_state"] = event.unsigned["replaces_state"]
event_unsigned = event_dict.get("unsigned", {})
return type(event)(
allowed_fields,
internal_metadata_dict=event.internal_metadata.get_dict()
)
if "age_ts" in event_unsigned:
unsigned["age_ts"] = event_unsigned["age_ts"]
if "replaces_state" in event_unsigned:
unsigned["replaces_state"] = event_unsigned["replaces_state"]
return allowed_fields
def _copy_field(src, dst, field):