From 9fbb20a531161652143028cde333429fe03b0343 Mon Sep 17 00:00:00 2001 From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> Date: Thu, 6 Jun 2019 17:33:11 +0100 Subject: Stop hardcoding trust of old matrix.org key (#5374) There are a few changes going on here: * We make checking the signature on a key server response optional: if no verify_keys are specified, we trust to TLS to validate the connection. * We change the default config so that it does not require responses to be signed by the old key. * We replace the old 'perspectives' config with 'trusted_key_servers', which is also formatted slightly differently. * We emit a warning to the logs every time we trust a key server response signed by the old key. --- synapse/config/key.py | 228 +++++++++++++++++++++++++++++++++++++++++--------- 1 file changed, 189 insertions(+), 39 deletions(-) (limited to 'synapse/config/key.py') diff --git a/synapse/config/key.py b/synapse/config/key.py index eb10259818..aba7092ccd 100644 --- a/synapse/config/key.py +++ b/synapse/config/key.py @@ -1,5 +1,6 @@ # -*- 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. @@ -17,6 +18,8 @@ import hashlib import logging import os +import attr +import jsonschema from signedjson.key import ( NACL_ED25519, decode_signing_key_base64, @@ -32,11 +35,27 @@ 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.""" + + logger = logging.getLogger(__name__) -class KeyConfig(Config): +@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): def read_config(self, config): # the signing key can be specified inline or in a separate file if "signing_key" in config: @@ -49,16 +68,27 @@ class KeyConfig(Config): config.get("old_signing_keys", {}) ) self.key_refresh_interval = self.parse_duration( - config.get("key_refresh_interval", "1d"), + config.get("key_refresh_interval", "1d") ) - self.perspectives = self.read_perspectives( - config.get("perspectives", {}).get("servers", { - "matrix.org": {"verify_keys": { - "ed25519:auto": { - "key": "Noi6WqcDj0QmPxCNQqgezwTlBKrfqehY1u2FyWP9uYw", - } - }} - }) + + # if neither trusted_key_servers nor perspectives are given, use the default. + if "perspectives" not in config and "trusted_key_servers" not in config: + 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)) + + # list of TrustedKeyServer objects + self.key_servers = list( + _parse_key_servers(key_servers, self.federation_verify_certificates) ) self.macaroon_secret_key = config.get( @@ -78,8 +108,9 @@ class KeyConfig(Config): # falsification of values self.form_secret = config.get("form_secret", None) - def default_config(self, config_dir_path, server_name, generate_secrets=False, - **kwargs): + def default_config( + self, config_dir_path, server_name, generate_secrets=False, **kwargs + ): base_key_name = os.path.join(config_dir_path, server_name) if generate_secrets: @@ -91,7 +122,8 @@ class KeyConfig(Config): macaroon_secret_key = "# macaroon_secret_key: " form_secret = "# form_secret: " - return """\ + 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. @@ -133,33 +165,53 @@ class KeyConfig(Config): # The trusted servers to download signing keys from. # - #perspectives: - # servers: - # "matrix.org": - # verify_keys: - # "ed25519:auto": - # key: "Noi6WqcDj0QmPxCNQqgezwTlBKrfqehY1u2FyWP9uYw" - """ % locals() - - def read_perspectives(self, perspectives_servers): - servers = {} - for server_name, server_config in perspectives_servers.items(): - for key_id, key_data in server_config["verify_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) - servers.setdefault(server_name, {})[key_id] = verify_key - return servers + # 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. + # + # 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" + # + # The default configuration is: + # + #trusted_key_servers: + # - server_name: "matrix.org" + """ + % locals() + ) def read_signing_key(self, signing_key_path): signing_keys = self.read_file(signing_key_path, "signing_key") try: return read_signing_keys(signing_keys.splitlines(True)) except Exception as e: - raise ConfigError( - "Error reading signing_key: %s" % (str(e)) - ) + raise ConfigError("Error reading signing_key: %s" % (str(e))) def read_old_signing_keys(self, old_signing_keys): keys = {} @@ -182,9 +234,7 @@ class KeyConfig(Config): if not self.path_exists(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),), - ) + 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: @@ -194,6 +244,106 @@ class KeyConfig(Config): 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,), + 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 verify_keys + and not server.get("accept_keys_insecurely") + and not federation_verify_certificates + ): + raise ConfigError(INSECURE_NOTARY_ERROR) + + yield result -- cgit 1.4.1 From 88d7182adaef8711bf3cc80ff604e566e517b6e6 Mon Sep 17 00:00:00 2001 From: Richard van der Hoff <1389908+richvdh@users.noreply.github.com> Date: Mon, 10 Jun 2019 10:33:00 +0100 Subject: Improve startup checks for insecure notary configs (#5392) It's not really a problem to trust notary responses signed by the old key so long as we are also doing TLS validation. This commit adds a check to the config parsing code at startup to check that we do not have the insecure matrix.org key without tls validation, and refuses to start without it. This allows us to remove the rather alarming-looking warning which happens at runtime. --- changelog.d/5392.bugfix | 1 + synapse/config/key.py | 27 +++++++++++++++++++++++---- synapse/crypto/keyring.py | 7 ------- 3 files changed, 24 insertions(+), 11 deletions(-) create mode 100644 changelog.d/5392.bugfix (limited to 'synapse/config/key.py') diff --git a/changelog.d/5392.bugfix b/changelog.d/5392.bugfix new file mode 100644 index 0000000000..295a7cfce1 --- /dev/null +++ b/changelog.d/5392.bugfix @@ -0,0 +1 @@ +Remove redundant warning about key server response validation. diff --git a/synapse/config/key.py b/synapse/config/key.py index aba7092ccd..424875feae 100644 --- a/synapse/config/key.py +++ b/synapse/config/key.py @@ -41,6 +41,15 @@ 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.""" + logger = logging.getLogger(__name__) @@ -340,10 +349,20 @@ def _parse_key_servers(key_servers, federation_verify_certificates): result.verify_keys[key_id] = verify_key if ( - not verify_keys - and not server.get("accept_keys_insecurely") - and not federation_verify_certificates + not federation_verify_certificates and + not server.get("accept_keys_insecurely") ): - raise ConfigError(INSECURE_NOTARY_ERROR) + _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) diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py index 96964b0d50..6f603f1961 100644 --- a/synapse/crypto/keyring.py +++ b/synapse/crypto/keyring.py @@ -750,13 +750,6 @@ class PerspectivesKeyFetcher(BaseV2KeyFetcher): verify_signed_json(response, perspective_name, perspective_keys[key_id]) verified = True - if perspective_name == "matrix.org" and key_id == "ed25519:auto": - logger.warning( - "Trusting trusted_key_server responses signed by the " - "compromised matrix.org signing key 'ed25519:auto'. " - "This is a placebo." - ) - if not verified: raise KeyLookupError( "Response not signed with a known key: signed with: %r, known keys: %r" -- cgit 1.4.1