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-rw-r--r--changelog.d/5232.misc2
-rw-r--r--changelog.d/5234.misc2
-rw-r--r--changelog.d/5235.misc2
-rw-r--r--changelog.d/5236.misc2
-rw-r--r--changelog.d/5237.misc2
-rw-r--r--changelog.d/5244.misc2
-rw-r--r--changelog.d/5250.misc2
-rw-r--r--changelog.d/5284.misc1
-rw-r--r--changelog.d/5296.misc2
-rw-r--r--changelog.d/5299.misc2
-rw-r--r--changelog.d/5317.bugfix1
-rw-r--r--changelog.d/5343.misc2
-rw-r--r--changelog.d/5347.misc3
-rw-r--r--changelog.d/5348.bugfix1
-rw-r--r--changelog.d/5352.bugfix1
-rw-r--r--changelog.d/5353.misc2
-rw-r--r--changelog.d/5354.bugfix2
-rw-r--r--changelog.d/5356.misc1
-rw-r--r--changelog.d/5357.doc1
-rw-r--r--changelog.d/5360.feature1
-rw-r--r--changelog.d/5362.bugfix1
-rw-r--r--docs/MSC1711_certificates_FAQ.md11
-rw-r--r--docs/sample_config.yaml16
-rw-r--r--synapse/api/room_versions.py20
-rw-r--r--synapse/config/server.py16
-rw-r--r--synapse/config/tls.py2
-rw-r--r--synapse/crypto/keyring.py112
-rw-r--r--synapse/federation/federation_base.py41
-rw-r--r--synapse/federation/transport/server.py4
-rw-r--r--synapse/groups/attestations.py4
-rw-r--r--synapse/handlers/federation.py58
-rw-r--r--synapse/handlers/presence.py11
-rw-r--r--synapse/handlers/stats.py18
-rw-r--r--synapse/rest/client/versions.py1
-rw-r--r--synapse/storage/events_worker.py37
-rw-r--r--tests/crypto/test_keyring.py18
-rw-r--r--tests/handlers/test_stats.py62
37 files changed, 345 insertions, 121 deletions
diff --git a/changelog.d/5232.misc b/changelog.d/5232.misc
index 1cdc71f095..8336bc55dc 100644
--- a/changelog.d/5232.misc
+++ b/changelog.d/5232.misc
@@ -1 +1 @@
-Run black on synapse.crypto.keyring.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5234.misc b/changelog.d/5234.misc
index 43fbd6f67c..8336bc55dc 100644
--- a/changelog.d/5234.misc
+++ b/changelog.d/5234.misc
@@ -1 +1 @@
-Rewrite store_server_verify_key to store several keys at once.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5235.misc b/changelog.d/5235.misc
index 2296ad2a4f..8336bc55dc 100644
--- a/changelog.d/5235.misc
+++ b/changelog.d/5235.misc
@@ -1 +1 @@
-Remove unused VerifyKey.expired and .time_added fields.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5236.misc b/changelog.d/5236.misc
index cb4417a9f4..8336bc55dc 100644
--- a/changelog.d/5236.misc
+++ b/changelog.d/5236.misc
@@ -1 +1 @@
-Simplify Keyring.process_v2_response.
\ No newline at end of file
+Preparatory work for key-validity features.
diff --git a/changelog.d/5237.misc b/changelog.d/5237.misc
index f4fe3b821b..8336bc55dc 100644
--- a/changelog.d/5237.misc
+++ b/changelog.d/5237.misc
@@ -1 +1 @@
-Store key validity time in the storage layer.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5244.misc b/changelog.d/5244.misc
index 9cc1fb869d..8336bc55dc 100644
--- a/changelog.d/5244.misc
+++ b/changelog.d/5244.misc
@@ -1 +1 @@
-Refactor synapse.crypto.keyring to use a KeyFetcher interface.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5250.misc b/changelog.d/5250.misc
index 575a299a82..8336bc55dc 100644
--- a/changelog.d/5250.misc
+++ b/changelog.d/5250.misc
@@ -1 +1 @@
-Simplification to Keyring.wait_for_previous_lookups.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5284.misc b/changelog.d/5284.misc
new file mode 100644
index 0000000000..c4d42ca3d9
--- /dev/null
+++ b/changelog.d/5284.misc
@@ -0,0 +1 @@
+Improve sample config for monthly active user blocking. 
diff --git a/changelog.d/5296.misc b/changelog.d/5296.misc
index a038a6f7f6..8336bc55dc 100644
--- a/changelog.d/5296.misc
+++ b/changelog.d/5296.misc
@@ -1 +1 @@
-Refactor keyring.VerifyKeyRequest to use attr.s.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5299.misc b/changelog.d/5299.misc
index 53297c768b..8336bc55dc 100644
--- a/changelog.d/5299.misc
+++ b/changelog.d/5299.misc
@@ -1 +1 @@
-Rewrite get_server_verify_keys, again.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5317.bugfix b/changelog.d/5317.bugfix
new file mode 100644
index 0000000000..2709375214
--- /dev/null
+++ b/changelog.d/5317.bugfix
@@ -0,0 +1 @@
+Fix handling of failures when processing incoming events where calling `/event_auth` on remote server fails.
diff --git a/changelog.d/5343.misc b/changelog.d/5343.misc
index dbee0f71b9..8336bc55dc 100644
--- a/changelog.d/5343.misc
+++ b/changelog.d/5343.misc
@@ -1 +1 @@
-Rename VerifyKeyRequest.deferred field.
+Preparatory work for key-validity features.
diff --git a/changelog.d/5347.misc b/changelog.d/5347.misc
index 436245fb11..8336bc55dc 100644
--- a/changelog.d/5347.misc
+++ b/changelog.d/5347.misc
@@ -1,2 +1 @@
-Various improvements to debug logging.
-
+Preparatory work for key-validity features.
diff --git a/changelog.d/5348.bugfix b/changelog.d/5348.bugfix
new file mode 100644
index 0000000000..8d396c7990
--- /dev/null
+++ b/changelog.d/5348.bugfix
@@ -0,0 +1 @@
+Add a new room version where the timestamps on events are checked against the validity periods on signing keys.
\ No newline at end of file
diff --git a/changelog.d/5352.bugfix b/changelog.d/5352.bugfix
new file mode 100644
index 0000000000..2ffefe5a68
--- /dev/null
+++ b/changelog.d/5352.bugfix
@@ -0,0 +1 @@
+Fix room stats and presence background updates to correctly handle missing events.
diff --git a/changelog.d/5353.misc b/changelog.d/5353.misc
new file mode 100644
index 0000000000..436245fb11
--- /dev/null
+++ b/changelog.d/5353.misc
@@ -0,0 +1,2 @@
+Various improvements to debug logging.
+
diff --git a/changelog.d/5354.bugfix b/changelog.d/5354.bugfix
new file mode 100644
index 0000000000..0c56032b30
--- /dev/null
+++ b/changelog.d/5354.bugfix
@@ -0,0 +1,2 @@
+Add a new room version where the timestamps on events are checked against the validity periods on signing keys.
+
diff --git a/changelog.d/5356.misc b/changelog.d/5356.misc
new file mode 100644
index 0000000000..8336bc55dc
--- /dev/null
+++ b/changelog.d/5356.misc
@@ -0,0 +1 @@
+Preparatory work for key-validity features.
diff --git a/changelog.d/5357.doc b/changelog.d/5357.doc
new file mode 100644
index 0000000000..27cba49641
--- /dev/null
+++ b/changelog.d/5357.doc
@@ -0,0 +1 @@
+Fix notes about ACME in the MSC1711 faq.
diff --git a/changelog.d/5360.feature b/changelog.d/5360.feature
new file mode 100644
index 0000000000..01fbb3b06d
--- /dev/null
+++ b/changelog.d/5360.feature
@@ -0,0 +1 @@
+Update /_matrix/client/versions to reference support for r0.5.0. 
diff --git a/changelog.d/5362.bugfix b/changelog.d/5362.bugfix
new file mode 100644
index 0000000000..1c8b19182c
--- /dev/null
+++ b/changelog.d/5362.bugfix
@@ -0,0 +1 @@
+Fix `federation_custom_ca_list` configuration option.
diff --git a/docs/MSC1711_certificates_FAQ.md b/docs/MSC1711_certificates_FAQ.md
index ebfb20f5c8..37f7f669c9 100644
--- a/docs/MSC1711_certificates_FAQ.md
+++ b/docs/MSC1711_certificates_FAQ.md
@@ -145,12 +145,11 @@ You can do this with a `.well-known` file as follows:
  1. Keep the SRV record in place - it is needed for backwards compatibility
     with Synapse 0.34 and earlier.
 
- 2. Give synapse a certificate corresponding to the target domain
-    (`customer.example.net` in the above example). Currently Synapse's ACME
-    support [does not support
-    this](https://github.com/matrix-org/synapse/issues/4552), so you will have
-    to acquire a certificate yourself and give it to Synapse via
-    `tls_certificate_path` and `tls_private_key_path`.
+  2. Give Synapse a certificate corresponding to the target domain
+    (`customer.example.net` in the above example). You can either use Synapse's 
+    built-in [ACME support](./ACME.md) for this (via the `domain` parameter in 
+    the `acme` section), or acquire a certificate yourself and give it to 
+    Synapse via `tls_certificate_path` and `tls_private_key_path`.
 
  3. Restart Synapse to ensure the new certificate is loaded.
 
diff --git a/docs/sample_config.yaml b/docs/sample_config.yaml
index 493ea9ee9e..0960b9b5ed 100644
--- a/docs/sample_config.yaml
+++ b/docs/sample_config.yaml
@@ -261,6 +261,22 @@ listeners:
 
 # Monthly Active User Blocking
 #
+# Used in cases where the admin or server owner wants to limit to the
+# number of monthly active users.
+#
+# 'limit_usage_by_mau' disables/enables monthly active user blocking. When
+# anabled and a limit is reached the server returns a 'ResourceLimitError'
+# with error type Codes.RESOURCE_LIMIT_EXCEEDED
+#
+# 'max_mau_value' is the hard limit of monthly active users above which
+# the server will start blocking user actions.
+#
+# 'mau_trial_days' is a means to add a grace period for active users. It
+# means that users must be active for this number of days before they
+# can be considered active and guards against the case where lots of users
+# sign up in a short space of time never to return after their initial
+# session.
+#
 #limit_usage_by_mau: False
 #max_mau_value: 50
 #mau_trial_days: 2
diff --git a/synapse/api/room_versions.py b/synapse/api/room_versions.py
index 4085bd10b9..d644803d38 100644
--- a/synapse/api/room_versions.py
+++ b/synapse/api/room_versions.py
@@ -50,6 +50,7 @@ class RoomVersion(object):
     disposition = attr.ib()     # str; one of the RoomDispositions
     event_format = attr.ib()    # int; one of the EventFormatVersions
     state_res = attr.ib()       # int; one of the StateResolutionVersions
+    enforce_key_validity = attr.ib()  # bool
 
 
 class RoomVersions(object):
@@ -58,30 +59,35 @@ class RoomVersions(object):
         RoomDisposition.STABLE,
         EventFormatVersions.V1,
         StateResolutionVersions.V1,
-    )
-    STATE_V2_TEST = RoomVersion(
-        "state-v2-test",
-        RoomDisposition.UNSTABLE,
-        EventFormatVersions.V1,
-        StateResolutionVersions.V2,
+        enforce_key_validity=False,
     )
     V2 = RoomVersion(
         "2",
         RoomDisposition.STABLE,
         EventFormatVersions.V1,
         StateResolutionVersions.V2,
+        enforce_key_validity=False,
     )
     V3 = RoomVersion(
         "3",
         RoomDisposition.STABLE,
         EventFormatVersions.V2,
         StateResolutionVersions.V2,
+        enforce_key_validity=False,
     )
     V4 = RoomVersion(
         "4",
         RoomDisposition.STABLE,
         EventFormatVersions.V3,
         StateResolutionVersions.V2,
+        enforce_key_validity=False,
+    )
+    V5 = RoomVersion(
+        "5",
+        RoomDisposition.STABLE,
+        EventFormatVersions.V3,
+        StateResolutionVersions.V2,
+        enforce_key_validity=True,
     )
 
 
@@ -90,7 +96,7 @@ KNOWN_ROOM_VERSIONS = {
         RoomVersions.V1,
         RoomVersions.V2,
         RoomVersions.V3,
-        RoomVersions.STATE_V2_TEST,
         RoomVersions.V4,
+        RoomVersions.V5,
     )
 }   # type: dict[str, RoomVersion]
diff --git a/synapse/config/server.py b/synapse/config/server.py
index e763e19e15..334921d421 100644
--- a/synapse/config/server.py
+++ b/synapse/config/server.py
@@ -585,6 +585,22 @@ class ServerConfig(Config):
 
         # Monthly Active User Blocking
         #
+        # Used in cases where the admin or server owner wants to limit to the
+        # number of monthly active users.
+        #
+        # 'limit_usage_by_mau' disables/enables monthly active user blocking. When
+        # anabled and a limit is reached the server returns a 'ResourceLimitError'
+        # with error type Codes.RESOURCE_LIMIT_EXCEEDED
+        #
+        # 'max_mau_value' is the hard limit of monthly active users above which
+        # the server will start blocking user actions.
+        #
+        # 'mau_trial_days' is a means to add a grace period for active users. It
+        # means that users must be active for this number of days before they
+        # can be considered active and guards against the case where lots of users
+        # sign up in a short space of time never to return after their initial
+        # session.
+        #
         #limit_usage_by_mau: False
         #max_mau_value: 50
         #mau_trial_days: 2
diff --git a/synapse/config/tls.py b/synapse/config/tls.py
index 72dd5926f9..94a53d05f9 100644
--- a/synapse/config/tls.py
+++ b/synapse/config/tls.py
@@ -107,7 +107,7 @@ class TlsConfig(Config):
             certs = []
             for ca_file in custom_ca_list:
                 logger.debug("Reading custom CA certificate file: %s", ca_file)
-                content = self.read_file(ca_file)
+                content = self.read_file(ca_file, "federation_custom_ca_list")
 
                 # Parse the CA certificates
                 try:
diff --git a/synapse/crypto/keyring.py b/synapse/crypto/keyring.py
index e94e71bdad..2b6b5913bc 100644
--- a/synapse/crypto/keyring.py
+++ b/synapse/crypto/keyring.py
@@ -60,9 +60,9 @@ logger = logging.getLogger(__name__)
 
 
 @attr.s(slots=True, cmp=False)
-class VerifyKeyRequest(object):
+class VerifyJsonRequest(object):
     """
-    A request for a verify key to verify a JSON object.
+    A request to verify a JSON object.
 
     Attributes:
         server_name(str): The name of the server to verify against.
@@ -85,11 +85,15 @@ class VerifyKeyRequest(object):
     """
 
     server_name = attr.ib()
-    key_ids = attr.ib()
     json_object = attr.ib()
     minimum_valid_until_ts = attr.ib()
+    request_name = attr.ib()
+    key_ids = attr.ib(init=False)
     key_ready = attr.ib(default=attr.Factory(defer.Deferred))
 
+    def __attrs_post_init__(self):
+        self.key_ids = signature_ids(self.json_object, self.server_name)
+
 
 class KeyLookupError(ValueError):
     pass
@@ -114,7 +118,9 @@ class Keyring(object):
         # These are regular, logcontext-agnostic Deferreds.
         self.key_downloads = {}
 
-    def verify_json_for_server(self, server_name, json_object, validity_time):
+    def verify_json_for_server(
+        self, server_name, json_object, validity_time, request_name
+    ):
         """Verify that a JSON object has been signed by a given server
 
         Args:
@@ -125,24 +131,31 @@ class Keyring(object):
             validity_time (int): timestamp at which we require the signing key to
                 be valid. (0 implies we don't care)
 
+            request_name (str): an identifier for this json object (eg, an event id)
+                for logging.
+
         Returns:
             Deferred[None]: completes if the the object was correctly signed, otherwise
                 errbacks with an error
         """
-        req = server_name, json_object, validity_time
-
-        return logcontext.make_deferred_yieldable(
-            self.verify_json_objects_for_server((req,))[0]
-        )
+        req = VerifyJsonRequest(server_name, json_object, validity_time, request_name)
+        requests = (req,)
+        return logcontext.make_deferred_yieldable(self._verify_objects(requests)[0])
 
     def verify_json_objects_for_server(self, server_and_json):
         """Bulk verifies signatures of json objects, bulk fetching keys as
         necessary.
 
         Args:
-            server_and_json (iterable[Tuple[str, dict, int]):
-                Iterable of triplets of (server_name, json_object, validity_time)
-                validity_time is a timestamp at which the signing key must be valid.
+            server_and_json (iterable[Tuple[str, dict, int, str]):
+                Iterable of (server_name, json_object, validity_time, request_name)
+                tuples.
+
+                validity_time is a timestamp at which the signing key must be
+                valid.
+
+                request_name is an identifier for this json object (eg, an event id)
+                for logging.
 
         Returns:
             List<Deferred[None]>: for each input triplet, a deferred indicating success
@@ -150,38 +163,54 @@ class Keyring(object):
                 server_name. The deferreds run their callbacks in the sentinel
                 logcontext.
         """
-        # a list of VerifyKeyRequests
-        verify_requests = []
+        return self._verify_objects(
+            VerifyJsonRequest(server_name, json_object, validity_time, request_name)
+            for server_name, json_object, validity_time, request_name in server_and_json
+        )
+
+    def _verify_objects(self, verify_requests):
+        """Does the work of verify_json_[objects_]for_server
+
+
+        Args:
+            verify_requests (iterable[VerifyJsonRequest]):
+                Iterable of verification requests.
+
+        Returns:
+            List<Deferred[None]>: for each input item, a deferred indicating success
+                or failure to verify each json object's signature for the given
+                server_name. The deferreds run their callbacks in the sentinel
+                logcontext.
+        """
+        # a list of VerifyJsonRequests which are awaiting a key lookup
+        key_lookups = []
         handle = preserve_fn(_handle_key_deferred)
 
-        def process(server_name, json_object, validity_time):
+        def process(verify_request):
             """Process an entry in the request list
 
-            Given a (server_name, json_object, validity_time) triplet from the request
-            list, adds a key request to verify_requests, and returns a deferred which
+            Adds a key request to key_lookups, and returns a deferred which
             will complete or fail (in the sentinel context) when verification completes.
             """
-            key_ids = signature_ids(json_object, server_name)
-
-            if not key_ids:
+            if not verify_request.key_ids:
                 return defer.fail(
                     SynapseError(
-                        400, "Not signed by %s" % (server_name,), Codes.UNAUTHORIZED
+                        400,
+                        "Not signed by %s" % (verify_request.server_name,),
+                        Codes.UNAUTHORIZED,
                     )
                 )
 
             logger.debug(
-                "Verifying for %s with key_ids %s, min_validity %i",
-                server_name,
-                key_ids,
-                validity_time,
+                "Verifying %s for %s with key_ids %s, min_validity %i",
+                verify_request.request_name,
+                verify_request.server_name,
+                verify_request.key_ids,
+                verify_request.minimum_valid_until_ts,
             )
 
             # add the key request to the queue, but don't start it off yet.
-            verify_request = VerifyKeyRequest(
-                server_name, key_ids, json_object, validity_time
-            )
-            verify_requests.append(verify_request)
+            key_lookups.append(verify_request)
 
             # now run _handle_key_deferred, which will wait for the key request
             # to complete and then do the verification.
@@ -190,13 +219,10 @@ class Keyring(object):
             # wrap it with preserve_fn (aka run_in_background)
             return handle(verify_request)
 
-        results = [
-            process(server_name, json_object, validity_time)
-            for server_name, json_object, validity_time in server_and_json
-        ]
+        results = [process(r) for r in verify_requests]
 
-        if verify_requests:
-            run_in_background(self._start_key_lookups, verify_requests)
+        if key_lookups:
+            run_in_background(self._start_key_lookups, key_lookups)
 
         return results
 
@@ -207,7 +233,7 @@ class Keyring(object):
         Once each fetch completes, verify_request.key_ready will be resolved.
 
         Args:
-            verify_requests (List[VerifyKeyRequest]):
+            verify_requests (List[VerifyJsonRequest]):
         """
 
         try:
@@ -308,7 +334,7 @@ class Keyring(object):
         with a SynapseError if none of the keys are found.
 
         Args:
-            verify_requests (list[VerifyKeyRequest]): list of verify requests
+            verify_requests (list[VerifyJsonRequest]): list of verify requests
         """
 
         remaining_requests = set(
@@ -357,7 +383,7 @@ class Keyring(object):
 
         Args:
             fetcher (KeyFetcher): fetcher to use to fetch the keys
-            remaining_requests (set[VerifyKeyRequest]): outstanding key requests.
+            remaining_requests (set[VerifyJsonRequest]): outstanding key requests.
                 Any successfully-completed requests will be removed from the list.
         """
         # dict[str, dict[str, int]]: keys to fetch.
@@ -376,7 +402,7 @@ class Keyring(object):
                 # the requests.
                 keys_for_server[key_id] = max(
                     keys_for_server.get(key_id, -1),
-                    verify_request.minimum_valid_until_ts
+                    verify_request.minimum_valid_until_ts,
                 )
 
         results = yield fetcher.get_keys(missing_keys)
@@ -386,7 +412,7 @@ class Keyring(object):
             server_name = verify_request.server_name
 
             # see if any of the keys we got this time are sufficient to
-            # complete this VerifyKeyRequest.
+            # complete this VerifyJsonRequest.
             result_keys = results.get(server_name, {})
             for key_id in verify_request.key_ids:
                 fetch_key_result = result_keys.get(key_id)
@@ -454,9 +480,7 @@ class BaseV2KeyFetcher(object):
         self.config = hs.get_config()
 
     @defer.inlineCallbacks
-    def process_v2_response(
-        self, from_server, response_json, time_added_ms
-    ):
+    def process_v2_response(self, from_server, response_json, time_added_ms):
         """Parse a 'Server Keys' structure from the result of a /key request
 
         This is used to parse either the entirety of the response from
@@ -852,7 +876,7 @@ def _handle_key_deferred(verify_request):
     """Waits for the key to become available, and then performs a verification
 
     Args:
-        verify_request (VerifyKeyRequest):
+        verify_request (VerifyJsonRequest):
 
     Returns:
         Deferred[None]
diff --git a/synapse/federation/federation_base.py b/synapse/federation/federation_base.py
index 4b38f7c759..fc5cfb7d83 100644
--- a/synapse/federation/federation_base.py
+++ b/synapse/federation/federation_base.py
@@ -223,9 +223,6 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
            the signatures are valid, or fail (with a SynapseError) if not.
     """
 
-    # (currently this is written assuming the v1 room structure; we'll probably want a
-    # separate function for checking v2 rooms)
-
     # we want to check that the event is signed by:
     #
     # (a) the sender's server
@@ -257,6 +254,10 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
         for p in pdus
     ]
 
+    v = KNOWN_ROOM_VERSIONS.get(room_version)
+    if not v:
+        raise RuntimeError("Unrecognized room version %s" % (room_version,))
+
     # First we check that the sender event is signed by the sender's domain
     # (except if its a 3pid invite, in which case it may be sent by any server)
     pdus_to_check_sender = [
@@ -264,10 +265,17 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
         if not _is_invite_via_3pid(p.pdu)
     ]
 
-    more_deferreds = keyring.verify_json_objects_for_server([
-        (p.sender_domain, p.redacted_pdu_json, 0)
-        for p in pdus_to_check_sender
-    ])
+    more_deferreds = keyring.verify_json_objects_for_server(
+        [
+            (
+                p.sender_domain,
+                p.redacted_pdu_json,
+                p.pdu.origin_server_ts if v.enforce_key_validity else 0,
+                p.pdu.event_id,
+            )
+            for p in pdus_to_check_sender
+        ]
+    )
 
     def sender_err(e, pdu_to_check):
         errmsg = "event id %s: unable to verify signature for sender %s: %s" % (
@@ -287,20 +295,23 @@ def _check_sigs_on_pdus(keyring, room_version, pdus):
     # event id's domain (normally only the case for joins/leaves), and add additional
     # checks. Only do this if the room version has a concept of event ID domain
     # (ie, the room version uses old-style non-hash event IDs).
-    v = KNOWN_ROOM_VERSIONS.get(room_version)
-    if not v:
-        raise RuntimeError("Unrecognized room version %s" % (room_version,))
-
     if v.event_format == EventFormatVersions.V1:
         pdus_to_check_event_id = [
             p for p in pdus_to_check
             if p.sender_domain != get_domain_from_id(p.pdu.event_id)
         ]
 
-        more_deferreds = keyring.verify_json_objects_for_server([
-            (get_domain_from_id(p.pdu.event_id), p.redacted_pdu_json, 0)
-            for p in pdus_to_check_event_id
-        ])
+        more_deferreds = keyring.verify_json_objects_for_server(
+            [
+                (
+                    get_domain_from_id(p.pdu.event_id),
+                    p.redacted_pdu_json,
+                    p.pdu.origin_server_ts if v.enforce_key_validity else 0,
+                    p.pdu.event_id,
+                )
+                for p in pdus_to_check_event_id
+            ]
+        )
 
         def event_err(e, pdu_to_check):
             errmsg = (
diff --git a/synapse/federation/transport/server.py b/synapse/federation/transport/server.py
index 0db8858cf1..949a5fb2aa 100644
--- a/synapse/federation/transport/server.py
+++ b/synapse/federation/transport/server.py
@@ -140,7 +140,9 @@ class Authenticator(object):
                 401, "Missing Authorization headers", Codes.UNAUTHORIZED,
             )
 
-        yield self.keyring.verify_json_for_server(origin, json_request, now)
+        yield self.keyring.verify_json_for_server(
+            origin, json_request, now, "Incoming request"
+        )
 
         logger.info("Request from %s", origin)
         request.authenticated_entity = origin
diff --git a/synapse/groups/attestations.py b/synapse/groups/attestations.py
index fa6b641ee1..e5dda1975f 100644
--- a/synapse/groups/attestations.py
+++ b/synapse/groups/attestations.py
@@ -101,7 +101,9 @@ class GroupAttestationSigning(object):
         if valid_until_ms < now:
             raise SynapseError(400, "Attestation expired")
 
-        yield self.keyring.verify_json_for_server(server_name, attestation, now)
+        yield self.keyring.verify_json_for_server(
+            server_name, attestation, now, "Group attestation"
+        )
 
     def create_attestation(self, group_id, user_id):
         """Create an attestation for the group_id and user_id with default
diff --git a/synapse/handlers/federation.py b/synapse/handlers/federation.py
index cf4fad7de0..ac5ca79143 100644
--- a/synapse/handlers/federation.py
+++ b/synapse/handlers/federation.py
@@ -35,6 +35,7 @@ from synapse.api.errors import (
     CodeMessageException,
     FederationDeniedError,
     FederationError,
+    RequestSendFailed,
     StoreError,
     SynapseError,
 )
@@ -2027,9 +2028,21 @@ class FederationHandler(BaseHandler):
         """
         room_version = yield self.store.get_room_version(event.room_id)
 
-        yield self._update_auth_events_and_context_for_auth(
-            origin, event, context, auth_events
-        )
+        try:
+            yield self._update_auth_events_and_context_for_auth(
+                origin, event, context, auth_events
+            )
+        except Exception:
+            # We don't really mind if the above fails, so lets not fail
+            # processing if it does. However, it really shouldn't fail so
+            # let's still log as an exception since we'll still want to fix
+            # any bugs.
+            logger.exception(
+                "Failed to double check auth events for %s with remote. "
+                "Ignoring failure and continuing processing of event.",
+                event.event_id,
+            )
+
         try:
             self.auth.check(room_version, event, auth_events=auth_events)
         except AuthError as e:
@@ -2042,6 +2055,15 @@ class FederationHandler(BaseHandler):
     ):
         """Helper for do_auth. See there for docs.
 
+        Checks whether a given event has the expected auth events. If it
+        doesn't then we talk to the remote server to compare state to see if
+        we can come to a consensus (e.g. if one server missed some valid
+        state).
+
+        This attempts to resovle any potential divergence of state between
+        servers, but is not essential and so failures should not block further
+        processing of the event.
+
         Args:
             origin (str):
             event (synapse.events.EventBase):
@@ -2088,9 +2110,15 @@ class FederationHandler(BaseHandler):
                 missing_auth,
             )
             try:
-                remote_auth_chain = yield self.federation_client.get_event_auth(
-                    origin, event.room_id, event.event_id
-                )
+                try:
+                    remote_auth_chain = yield self.federation_client.get_event_auth(
+                        origin, event.room_id, event.event_id
+                    )
+                except RequestSendFailed as e:
+                    # The other side isn't around or doesn't implement the
+                    # endpoint, so lets just bail out.
+                    logger.info("Failed to get event auth from remote: %s", e)
+                    return
 
                 seen_remotes = yield self.store.have_seen_events(
                     [e.event_id for e in remote_auth_chain]
@@ -2236,12 +2264,18 @@ class FederationHandler(BaseHandler):
 
         try:
             # 2. Get remote difference.
-            result = yield self.federation_client.query_auth(
-                origin,
-                event.room_id,
-                event.event_id,
-                local_auth_chain,
-            )
+            try:
+                result = yield self.federation_client.query_auth(
+                    origin,
+                    event.room_id,
+                    event.event_id,
+                    local_auth_chain,
+                )
+            except RequestSendFailed as e:
+                # The other side isn't around or doesn't implement the
+                # endpoint, so lets just bail out.
+                logger.info("Failed to query auth from remote: %s", e)
+                return
 
             seen_remotes = yield self.store.have_seen_events(
                 [e.event_id for e in result["auth_chain"]]
diff --git a/synapse/handlers/presence.py b/synapse/handlers/presence.py
index 6209858bbb..e49c8203ef 100644
--- a/synapse/handlers/presence.py
+++ b/synapse/handlers/presence.py
@@ -828,14 +828,17 @@ class PresenceHandler(object):
                 # joins.
                 continue
 
-            event = yield self.store.get_event(event_id)
-            if event.content.get("membership") != Membership.JOIN:
+            event = yield self.store.get_event(event_id, allow_none=True)
+            if not event or event.content.get("membership") != Membership.JOIN:
                 # We only care about joins
                 continue
 
             if prev_event_id:
-                prev_event = yield self.store.get_event(prev_event_id)
-                if prev_event.content.get("membership") == Membership.JOIN:
+                prev_event = yield self.store.get_event(prev_event_id, allow_none=True)
+                if (
+                    prev_event
+                    and prev_event.content.get("membership") == Membership.JOIN
+                ):
                     # Ignore changes to join events.
                     continue
 
diff --git a/synapse/handlers/stats.py b/synapse/handlers/stats.py
index 0e92b405ba..7ad16c8566 100644
--- a/synapse/handlers/stats.py
+++ b/synapse/handlers/stats.py
@@ -115,6 +115,7 @@ class StatsHandler(StateDeltasHandler):
             event_id = delta["event_id"]
             stream_id = delta["stream_id"]
             prev_event_id = delta["prev_event_id"]
+            stream_pos = delta["stream_id"]
 
             logger.debug("Handling: %r %r, %s", typ, state_key, event_id)
 
@@ -136,10 +137,15 @@ class StatsHandler(StateDeltasHandler):
             event_content = {}
 
             if event_id is not None:
-                event_content = (yield self.store.get_event(event_id)).content or {}
+                event = yield self.store.get_event(event_id, allow_none=True)
+                if event:
+                    event_content = event.content or {}
+
+            # We use stream_pos here rather than fetch by event_id as event_id
+            # may be None
+            now = yield self.store.get_received_ts_by_stream_pos(stream_pos)
 
             # quantise time to the nearest bucket
-            now = yield self.store.get_received_ts(event_id)
             now = (now // 1000 // self.stats_bucket_size) * self.stats_bucket_size
 
             if typ == EventTypes.Member:
@@ -149,9 +155,11 @@ class StatsHandler(StateDeltasHandler):
                 # compare them.
                 prev_event_content = {}
                 if prev_event_id is not None:
-                    prev_event_content = (
-                        yield self.store.get_event(prev_event_id)
-                    ).content
+                    prev_event = yield self.store.get_event(
+                        prev_event_id, allow_none=True,
+                    )
+                    if prev_event:
+                        prev_event_content = prev_event.content
 
                 membership = event_content.get("membership", Membership.LEAVE)
                 prev_membership = prev_event_content.get("membership", Membership.LEAVE)
diff --git a/synapse/rest/client/versions.py b/synapse/rest/client/versions.py
index 27e7cbf3cc..babbf6a23c 100644
--- a/synapse/rest/client/versions.py
+++ b/synapse/rest/client/versions.py
@@ -39,6 +39,7 @@ class VersionsRestServlet(RestServlet):
                 "r0.2.0",
                 "r0.3.0",
                 "r0.4.0",
+                "r0.5.0",
             ],
             # as per MSC1497:
             "unstable_features": {
diff --git a/synapse/storage/events_worker.py b/synapse/storage/events_worker.py
index 1782428048..cc7df5cf14 100644
--- a/synapse/storage/events_worker.py
+++ b/synapse/storage/events_worker.py
@@ -78,6 +78,43 @@ class EventsWorkerStore(SQLBaseStore):
             desc="get_received_ts",
         )
 
+    def get_received_ts_by_stream_pos(self, stream_ordering):
+        """Given a stream ordering get an approximate timestamp of when it
+        happened.
+
+        This is done by simply taking the received ts of the first event that
+        has a stream ordering greater than or equal to the given stream pos.
+        If none exists returns the current time, on the assumption that it must
+        have happened recently.
+
+        Args:
+            stream_ordering (int)
+
+        Returns:
+            Deferred[int]
+        """
+
+        def _get_approximate_received_ts_txn(txn):
+            sql = """
+                SELECT received_ts FROM events
+                WHERE stream_ordering >= ?
+                LIMIT 1
+            """
+
+            txn.execute(sql, (stream_ordering,))
+            row = txn.fetchone()
+            if row and row[0]:
+                ts = row[0]
+            else:
+                ts = self.clock.time_msec()
+
+            return ts
+
+        return self.runInteraction(
+            "get_approximate_received_ts",
+            _get_approximate_received_ts_txn,
+        )
+
     @defer.inlineCallbacks
     def get_event(
         self,
diff --git a/tests/crypto/test_keyring.py b/tests/crypto/test_keyring.py
index 4cff7e36c8..18121f4f6c 100644
--- a/tests/crypto/test_keyring.py
+++ b/tests/crypto/test_keyring.py
@@ -134,7 +134,7 @@ class KeyringTestCase(unittest.HomeserverTestCase):
                 context_11.request = "11"
 
                 res_deferreds = kr.verify_json_objects_for_server(
-                    [("server10", json1, 0), ("server11", {}, 0)]
+                    [("server10", json1, 0, "test10"), ("server11", {}, 0, "test11")]
                 )
 
                 # the unsigned json should be rejected pretty quickly
@@ -171,7 +171,7 @@ class KeyringTestCase(unittest.HomeserverTestCase):
                 self.http_client.post_json.return_value = defer.Deferred()
 
                 res_deferreds_2 = kr.verify_json_objects_for_server(
-                    [("server10", json1, 0)]
+                    [("server10", json1, 0, "test")]
                 )
                 res_deferreds_2[0].addBoth(self.check_context, None)
                 yield logcontext.make_deferred_yieldable(res_deferreds_2[0])
@@ -205,11 +205,11 @@ class KeyringTestCase(unittest.HomeserverTestCase):
         signedjson.sign.sign_json(json1, "server9", key1)
 
         # should fail immediately on an unsigned object
-        d = _verify_json_for_server(kr, "server9", {}, 0)
+        d = _verify_json_for_server(kr, "server9", {}, 0, "test unsigned")
         self.failureResultOf(d, SynapseError)
 
         # should suceed on a signed object
-        d = _verify_json_for_server(kr, "server9", json1, 500)
+        d = _verify_json_for_server(kr, "server9", json1, 500, "test signed")
         # self.assertFalse(d.called)
         self.get_success(d)
 
@@ -239,7 +239,7 @@ class KeyringTestCase(unittest.HomeserverTestCase):
         # the first request should succeed; the second should fail because the key
         # has expired
         results = kr.verify_json_objects_for_server(
-            [("server1", json1, 500), ("server1", json1, 1500)]
+            [("server1", json1, 500, "test1"), ("server1", json1, 1500, "test2")]
         )
         self.assertEqual(len(results), 2)
         self.get_success(results[0])
@@ -284,7 +284,7 @@ class KeyringTestCase(unittest.HomeserverTestCase):
         signedjson.sign.sign_json(json1, "server1", key1)
 
         results = kr.verify_json_objects_for_server(
-            [("server1", json1, 1200), ("server1", json1, 1500)]
+            [("server1", json1, 1200, "test1"), ("server1", json1, 1500, "test2")]
         )
         self.assertEqual(len(results), 2)
         self.get_success(results[0])
@@ -522,16 +522,14 @@ def run_in_context(f, *args, **kwargs):
     defer.returnValue(rv)
 
 
-def _verify_json_for_server(keyring, server_name, json_object, validity_time):
+def _verify_json_for_server(kr, *args):
     """thin wrapper around verify_json_for_server which makes sure it is wrapped
     with the patched defer.inlineCallbacks.
     """
 
     @defer.inlineCallbacks
     def v():
-        rv1 = yield keyring.verify_json_for_server(
-            server_name, json_object, validity_time
-        )
+        rv1 = yield kr.verify_json_for_server(*args)
         defer.returnValue(rv1)
 
     return run_in_context(v)
diff --git a/tests/handlers/test_stats.py b/tests/handlers/test_stats.py
index 249aba3d59..2710c991cf 100644
--- a/tests/handlers/test_stats.py
+++ b/tests/handlers/test_stats.py
@@ -204,7 +204,7 @@ class StatsRoomTests(unittest.HomeserverTestCase):
             "a2": {"membership": "not a real thing"},
         }
 
-        def get_event(event_id):
+        def get_event(event_id, allow_none=True):
             m = Mock()
             m.content = events[event_id]
             d = defer.Deferred()
@@ -224,7 +224,7 @@ class StatsRoomTests(unittest.HomeserverTestCase):
                 "room_id": "room",
                 "event_id": "a1",
                 "prev_event_id": "a2",
-                "stream_id": "bleb",
+                "stream_id": 60,
             }
         ]
 
@@ -241,7 +241,7 @@ class StatsRoomTests(unittest.HomeserverTestCase):
                 "room_id": "room",
                 "event_id": "a2",
                 "prev_event_id": "a1",
-                "stream_id": "bleb",
+                "stream_id": 100,
             }
         ]
 
@@ -249,3 +249,59 @@ class StatsRoomTests(unittest.HomeserverTestCase):
         self.assertEqual(
             f.value.args[0], "'not a real thing' is not a valid membership"
         )
+
+    def test_redacted_prev_event(self):
+        """
+        If the prev_event does not exist, then it is assumed to be a LEAVE.
+        """
+        u1 = self.register_user("u1", "pass")
+        u1_token = self.login("u1", "pass")
+
+        room_1 = self.helper.create_room_as(u1, tok=u1_token)
+
+        # Do the initial population of the user directory via the background update
+        self._add_background_updates()
+
+        while not self.get_success(self.store.has_completed_background_updates()):
+            self.get_success(self.store.do_next_background_update(100), by=0.1)
+
+        events = {
+            "a1": None,
+            "a2": {"membership": Membership.JOIN},
+        }
+
+        def get_event(event_id, allow_none=True):
+            if events.get(event_id):
+                m = Mock()
+                m.content = events[event_id]
+            else:
+                m = None
+            d = defer.Deferred()
+            self.reactor.callLater(0.0, d.callback, m)
+            return d
+
+        def get_received_ts(event_id):
+            return defer.succeed(1)
+
+        self.store.get_received_ts = get_received_ts
+        self.store.get_event = get_event
+
+        deltas = [
+            {
+                "type": EventTypes.Member,
+                "state_key": "some_user:test",
+                "room_id": room_1,
+                "event_id": "a2",
+                "prev_event_id": "a1",
+                "stream_id": 100,
+            }
+        ]
+
+        # Handle our fake deltas, which has a user going from LEAVE -> JOIN.
+        self.get_success(self.handler._handle_deltas(deltas))
+
+        # One delta, with two joined members -- the room creator, and our fake
+        # user.
+        r = self.get_success(self.store.get_deltas_for_room(room_1, 0))
+        self.assertEqual(len(r), 1)
+        self.assertEqual(r[0]["joined_members"], 2)