# -*- coding: utf-8 -*- # 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(object): # 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': " + e.message) 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)