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synapse/synapse/config/key.py

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# Copyright 2015, 2016 OpenMarket 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 hashlib
import logging
import os
import attr
import jsonschema
from signedjson.key import (
NACL_ED25519,
decode_signing_key_base64,
decode_verify_key_bytes,
generate_signing_key,
is_signing_algorithm_supported,
read_signing_keys,
write_signing_keys,
)
from unpaddedbase64 import decode_base64
from synapse.util.stringutils import random_string, random_string_with_symbols
from ._base import Config, ConfigError
INSECURE_NOTARY_ERROR = """\
Your server is configured to accept key server responses without signature
validation or TLS certificate validation. This is likely to be very insecure. If
you are *sure* you want to do this, set 'accept_keys_insecurely' on the
keyserver configuration."""
RELYING_ON_MATRIX_KEY_ERROR = """\
Your server is configured to accept key server responses without TLS certificate
validation, and which are only signed by the old (possibly compromised)
matrix.org signing key 'ed25519:auto'. This likely isn't what you want to do,
and you should enable 'federation_verify_certificates' in your configuration.
If you are *sure* you want to do this, set 'accept_keys_insecurely' on the
trusted_key_server configuration."""
TRUSTED_KEY_SERVER_NOT_CONFIGURED_WARN = """\
Synapse requires that a list of trusted key servers are specified in order to
provide signing keys for other servers in the federation.
This homeserver does not have a trusted key server configured in
homeserver.yaml and will fall back to the default of 'matrix.org'.
Trusted key servers should be long-lived and stable which makes matrix.org a
good choice for many admins, but some admins may wish to choose another. To
suppress this warning, the admin should set 'trusted_key_servers' in
homeserver.yaml to their desired key server and 'suppress_key_server_warning'
to 'true'.
In a future release the software-defined default will be removed entirely and
the trusted key server will be defined exclusively by the value of
'trusted_key_servers'.
--------------------------------------------------------------------------------"""
TRUSTED_KEY_SERVER_CONFIGURED_AS_M_ORG_WARN = """\
This server is configured to use 'matrix.org' as its trusted key server via the
'trusted_key_servers' config option. 'matrix.org' is a good choice for a key
server since it is long-lived, stable and trusted. However, some admins may
wish to use another server for this purpose.
To suppress this warning and continue using 'matrix.org', admins should set
'suppress_key_server_warning' to 'true' in homeserver.yaml.
--------------------------------------------------------------------------------"""
logger = logging.getLogger(__name__)
@attr.s
class TrustedKeyServer:
# string: name of the server.
server_name = attr.ib()
# dict[str,VerifyKey]|None: map from key id to key object, or None to disable
# signature verification.
verify_keys = attr.ib(default=None)
class KeyConfig(Config):
section = "key"
def read_config(self, config, config_dir_path, **kwargs):
# the signing key can be specified inline or in a separate file
if "signing_key" in config:
self.signing_key = read_signing_keys([config["signing_key"]])
else:
signing_key_path = config.get("signing_key_path")
if signing_key_path is None:
signing_key_path = os.path.join(
config_dir_path, config["server_name"] + ".signing.key"
)
self.signing_key = self.read_signing_keys(signing_key_path, "signing_key")
self.old_signing_keys = self.read_old_signing_keys(
config.get("old_signing_keys")
)
self.key_refresh_interval = self.parse_duration(
config.get("key_refresh_interval", "1d")
)
suppress_key_server_warning = config.get("suppress_key_server_warning", False)
key_server_signing_keys_path = config.get("key_server_signing_keys_path")
if key_server_signing_keys_path:
self.key_server_signing_keys = self.read_signing_keys(
key_server_signing_keys_path, "key_server_signing_keys_path"
)
else:
self.key_server_signing_keys = list(self.signing_key)
# if neither trusted_key_servers nor perspectives are given, use the default.
if "perspectives" not in config and "trusted_key_servers" not in config:
logger.warning(TRUSTED_KEY_SERVER_NOT_CONFIGURED_WARN)
key_servers = [{"server_name": "matrix.org"}]
else:
key_servers = config.get("trusted_key_servers", [])
if not isinstance(key_servers, list):
raise ConfigError(
"trusted_key_servers, if given, must be a list, not a %s"
% (type(key_servers).__name__,)
)
# merge the 'perspectives' config into the 'trusted_key_servers' config.
key_servers.extend(_perspectives_to_key_servers(config))
if not suppress_key_server_warning and "matrix.org" in (
s["server_name"] for s in key_servers
):
logger.warning(TRUSTED_KEY_SERVER_CONFIGURED_AS_M_ORG_WARN)
# list of TrustedKeyServer objects
self.key_servers = list(
_parse_key_servers(key_servers, self.federation_verify_certificates)
)
self.macaroon_secret_key = config.get(
"macaroon_secret_key", self.registration_shared_secret
)
if not self.macaroon_secret_key:
# Unfortunately, there are people out there that don't have this
# set. Lets just be "nice" and derive one from their secret key.
logger.warning("Config is missing macaroon_secret_key")
seed = bytes(self.signing_key[0])
self.macaroon_secret_key = hashlib.sha256(seed).digest()
# a secret which is used to calculate HMACs for form values, to stop
# falsification of values
self.form_secret = config.get("form_secret", None)
def generate_config_section(
self, config_dir_path, server_name, generate_secrets=False, **kwargs
):
base_key_name = os.path.join(config_dir_path, server_name)
if generate_secrets:
macaroon_secret_key = 'macaroon_secret_key: "%s"' % (
random_string_with_symbols(50),
)
form_secret = 'form_secret: "%s"' % random_string_with_symbols(50)
else:
macaroon_secret_key = "#macaroon_secret_key: <PRIVATE STRING>"
form_secret = "#form_secret: <PRIVATE STRING>"
return (
"""\
# a secret which is used to sign access tokens. If none is specified,
# the registration_shared_secret is used, if one is given; otherwise,
# a secret key is derived from the signing key.
#
%(macaroon_secret_key)s
# a secret which is used to calculate HMACs for form values, to stop
# falsification of values. Must be specified for the User Consent
# forms to work.
#
%(form_secret)s
## Signing Keys ##
# Path to the signing key to sign messages with
#
signing_key_path: "%(base_key_name)s.signing.key"
# The keys that the server used to sign messages with but won't use
# to sign new messages.
#
old_signing_keys:
# For each key, `key` should be the base64-encoded public key, and
# `expired_ts`should be the time (in milliseconds since the unix epoch) that
# it was last used.
#
# It is possible to build an entry from an old signing.key file using the
# `export_signing_key` script which is provided with synapse.
#
# For example:
#
#"ed25519:id": { key: "base64string", expired_ts: 123456789123 }
# How long key response published by this server is valid for.
# Used to set the valid_until_ts in /key/v2 APIs.
# Determines how quickly servers will query to check which keys
# are still valid.
#
#key_refresh_interval: 1d
# The trusted servers to download signing keys from.
#
# When we need to fetch a signing key, each server is tried in parallel.
#
# Normally, the connection to the key server is validated via TLS certificates.
# Additional security can be provided by configuring a `verify key`, which
# will make synapse check that the response is signed by that key.
#
# This setting supercedes an older setting named `perspectives`. The old format
# is still supported for backwards-compatibility, but it is deprecated.
#
# 'trusted_key_servers' defaults to matrix.org, but using it will generate a
# warning on start-up. To suppress this warning, set
# 'suppress_key_server_warning' to true.
#
# Options for each entry in the list include:
#
# server_name: the name of the server. required.
#
# verify_keys: an optional map from key id to base64-encoded public key.
# If specified, we will check that the response is signed by at least
# one of the given keys.
#
# accept_keys_insecurely: a boolean. Normally, if `verify_keys` is unset,
# and federation_verify_certificates is not `true`, synapse will refuse
# to start, because this would allow anyone who can spoof DNS responses
# to masquerade as the trusted key server. If you know what you are doing
# and are sure that your network environment provides a secure connection
# to the key server, you can set this to `true` to override this
# behaviour.
#
# An example configuration might look like:
#
#trusted_key_servers:
# - server_name: "my_trusted_server.example.com"
# verify_keys:
# "ed25519:auto": "abcdefghijklmnopqrstuvwxyzabcdefghijklmopqr"
# - server_name: "my_other_trusted_server.example.com"
#
trusted_key_servers:
- server_name: "matrix.org"
# Uncomment the following to disable the warning that is emitted when the
# trusted_key_servers include 'matrix.org'. See above.
#
#suppress_key_server_warning: true
# The signing keys to use when acting as a trusted key server. If not specified
# defaults to the server signing key.
#
# Can contain multiple keys, one per line.
#
#key_server_signing_keys_path: "key_server_signing_keys.key"
"""
% locals()
)
def read_signing_keys(self, signing_key_path, name):
"""Read the signing keys in the given path.
Args:
signing_key_path (str)
name (str): Associated config key name
Returns:
list[SigningKey]
"""
signing_keys = self.read_file(signing_key_path, name)
try:
return read_signing_keys(signing_keys.splitlines(True))
except Exception as e:
raise ConfigError("Error reading %s: %s" % (name, str(e)))
def read_old_signing_keys(self, old_signing_keys):
if old_signing_keys is None:
return {}
keys = {}
for key_id, key_data in old_signing_keys.items():
if is_signing_algorithm_supported(key_id):
key_base64 = key_data["key"]
key_bytes = decode_base64(key_base64)
verify_key = decode_verify_key_bytes(key_id, key_bytes)
verify_key.expired_ts = key_data["expired_ts"]
keys[key_id] = verify_key
else:
raise ConfigError(
"Unsupported signing algorithm for old key: %r" % (key_id,)
)
return keys
def generate_files(self, config, config_dir_path):
if "signing_key" in config:
return
signing_key_path = config.get("signing_key_path")
if signing_key_path is None:
signing_key_path = os.path.join(
config_dir_path, config["server_name"] + ".signing.key"
)
if not self.path_exists(signing_key_path):
print("Generating signing key file %s" % (signing_key_path,))
with open(signing_key_path, "w") as signing_key_file:
key_id = "a_" + random_string(4)
write_signing_keys(signing_key_file, (generate_signing_key(key_id),))
else:
signing_keys = self.read_file(signing_key_path, "signing_key")
if len(signing_keys.split("\n")[0].split()) == 1:
# handle keys in the old format.
key_id = "a_" + random_string(4)
key = decode_signing_key_base64(
NACL_ED25519, key_id, signing_keys.split("\n")[0]
)
with open(signing_key_path, "w") as signing_key_file:
write_signing_keys(signing_key_file, (key,))
def _perspectives_to_key_servers(config):
"""Convert old-style 'perspectives' configs into new-style 'trusted_key_servers'
Returns an iterable of entries to add to trusted_key_servers.
"""
# 'perspectives' looks like:
#
# {
# "servers": {
# "matrix.org": {
# "verify_keys": {
# "ed25519:auto": {
# "key": "Noi6WqcDj0QmPxCNQqgezwTlBKrfqehY1u2FyWP9uYw"
# }
# }
# }
# }
# }
#
# 'trusted_keys' looks like:
#
# [
# {
# "server_name": "matrix.org",
# "verify_keys": {
# "ed25519:auto": "Noi6WqcDj0QmPxCNQqgezwTlBKrfqehY1u2FyWP9uYw",
# }
# }
# ]
perspectives_servers = config.get("perspectives", {}).get("servers", {})
for server_name, server_opts in perspectives_servers.items():
trusted_key_server_entry = {"server_name": server_name}
verify_keys = server_opts.get("verify_keys")
if verify_keys is not None:
trusted_key_server_entry["verify_keys"] = {
key_id: key_data["key"] for key_id, key_data in verify_keys.items()
}
yield trusted_key_server_entry
TRUSTED_KEY_SERVERS_SCHEMA = {
"$schema": "http://json-schema.org/draft-04/schema#",
"description": "schema for the trusted_key_servers setting",
"type": "array",
"items": {
"type": "object",
"properties": {
"server_name": {"type": "string"},
"verify_keys": {
"type": "object",
# each key must be a base64 string
"additionalProperties": {"type": "string"},
},
},
"required": ["server_name"],
},
}
def _parse_key_servers(key_servers, federation_verify_certificates):
try:
jsonschema.validate(key_servers, TRUSTED_KEY_SERVERS_SCHEMA)
except jsonschema.ValidationError as e:
raise ConfigError(
"Unable to parse 'trusted_key_servers': {}".format(
e.message # noqa: B306, jsonschema.ValidationError.message is a valid attribute
)
)
for server in key_servers:
server_name = server["server_name"]
result = TrustedKeyServer(server_name=server_name)
verify_keys = server.get("verify_keys")
if verify_keys is not None:
result.verify_keys = {}
for key_id, key_base64 in verify_keys.items():
if not is_signing_algorithm_supported(key_id):
raise ConfigError(
"Unsupported signing algorithm on key %s for server %s in "
"trusted_key_servers" % (key_id, server_name)
)
try:
key_bytes = decode_base64(key_base64)
verify_key = decode_verify_key_bytes(key_id, key_bytes)
except Exception as e:
raise ConfigError(
"Unable to parse key %s for server %s in "
"trusted_key_servers: %s" % (key_id, server_name, e)
)
result.verify_keys[key_id] = verify_key
if not federation_verify_certificates and not server.get(
"accept_keys_insecurely"
):
_assert_keyserver_has_verify_keys(result)
yield result
def _assert_keyserver_has_verify_keys(trusted_key_server):
if not trusted_key_server.verify_keys:
raise ConfigError(INSECURE_NOTARY_ERROR)
# also check that they are not blindly checking the old matrix.org key
if trusted_key_server.server_name == "matrix.org" and any(
key_id == "ed25519:auto" for key_id in trusted_key_server.verify_keys
):
raise ConfigError(RELYING_ON_MATRIX_KEY_ERROR)
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