Cross-signing fixes, notifications via sync, federation (#1974)

* Initial work on signing key update EDUs

* Fix build

* Produce/consume EDUs

* Producer logging

* Only produce key change notifications for local users

* Better naming

* Try to notify sync

* Enable feature

* Use key change topic

* Don't bother verifying signatures, validate key lengths if we can, notifier fixes

* Copyright notices

* Remove tests from whitelist until matrix-org/sytest#1117

* Some review comment fixes

* Update to matrix-org/gomatrixserverlib@f9416ac

* Remove unneeded parameter

clientapi/jsonerror/jsonerror.go

@@ -131,6 +131,12 @@ func InvalidSignature(msg string) *MatrixError {
 	return &MatrixError{"M_INVALID_SIGNATURE", msg}
 }
 
+// InvalidParam is an error that is returned when a parameter was invalid,
+// traditionally with cross-signing.
+func InvalidParam(msg string) *MatrixError {
+	return &MatrixError{"M_INVALID_PARAM", msg}
+}
+
 // MissingParam is an error that is returned when a parameter was incorrect,
 // traditionally with cross-signing.
 func MissingParam(msg string) *MatrixError {

clientapi/routing/key_crosssigning.go

@@ -73,6 +73,11 @@ func UploadCrossSigningDeviceKeys(
 				Code: http.StatusBadRequest,
 				JSON: jsonerror.MissingParam(err.Error()),
 			}
+		case err.IsInvalidParam:
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.InvalidParam(err.Error()),
+			}
 		default:
 			return util.JSONResponse{
 				Code: http.StatusBadRequest,
@@ -110,6 +115,11 @@ func UploadCrossSigningDeviceSignatures(req *http.Request, keyserverAPI api.KeyI
 				Code: http.StatusBadRequest,
 				JSON: jsonerror.MissingParam(err.Error()),
 			}
+		case err.IsInvalidParam:
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.InvalidParam(err.Error()),
+			}
 		default:
 			return util.JSONResponse{
 				Code: http.StatusBadRequest,

clientapi/routing/routing.go

@@ -65,7 +65,7 @@ func Setup(
 	userInteractiveAuth := auth.NewUserInteractive(accountDB.GetAccountByPassword, cfg)
 
 	unstableFeatures := map[string]bool{
-		//"org.matrix.e2e_cross_signing": true,
+		"org.matrix.e2e_cross_signing": true,
 	}
 	for _, msc := range cfg.MSCs.MSCs {
 		unstableFeatures["org.matrix."+msc] = true

eduserver/api/input.go

@@ -75,6 +75,12 @@ type InputReceiptEventRequest struct {
 // InputReceiptEventResponse is a response to InputReceiptEventRequest
 type InputReceiptEventResponse struct{}
 
+type InputCrossSigningKeyUpdateRequest struct {
+	CrossSigningKeyUpdate `json:"signing_keys"`
+}
+
+type InputCrossSigningKeyUpdateResponse struct{}
+
 // EDUServerInputAPI is used to write events to the typing server.
 type EDUServerInputAPI interface {
 	InputTypingEvent(
@@ -94,4 +100,10 @@ type EDUServerInputAPI interface {
 		request *InputReceiptEventRequest,
 		response *InputReceiptEventResponse,
 	) error
+
+	InputCrossSigningKeyUpdate(
+		ctx context.Context,
+		request *InputCrossSigningKeyUpdateRequest,
+		response *InputCrossSigningKeyUpdateResponse,
+	) error
 }

eduserver/api/output.go

@@ -33,14 +33,6 @@ type OutputTypingEvent struct {
 	ExpireTime *time.Time
 }
 
-// TypingEvent represents a matrix edu event of type 'm.typing'.
-type TypingEvent struct {
-	Type   string `json:"type"`
-	RoomID string `json:"room_id"`
-	UserID string `json:"user_id"`
-	Typing bool   `json:"typing"`
-}
-
 // OutputSendToDeviceEvent is an entry in the send-to-device output kafka log.
 // This contains the full event content, along with the user ID and device ID
 // to which it is destined.
@@ -50,14 +42,6 @@ type OutputSendToDeviceEvent struct {
 	gomatrixserverlib.SendToDeviceEvent
 }
 
-type ReceiptEvent struct {
-	UserID    string                      `json:"user_id"`
-	RoomID    string                      `json:"room_id"`
-	EventID   string                      `json:"event_id"`
-	Type      string                      `json:"type"`
-	Timestamp gomatrixserverlib.Timestamp `json:"timestamp"`
-}
-
 // OutputReceiptEvent is an entry in the receipt output kafka log
 type OutputReceiptEvent struct {
 	UserID    string                      `json:"user_id"`
@@ -67,21 +51,7 @@ type OutputReceiptEvent struct {
 	Timestamp gomatrixserverlib.Timestamp `json:"timestamp"`
 }
 
-// Helper structs for receipts json creation
-type ReceiptMRead struct {
-	User map[string]ReceiptTS `json:"m.read"`
-}
-
-type ReceiptTS struct {
-	TS gomatrixserverlib.Timestamp `json:"ts"`
-}
-
-// FederationSender output
-type FederationReceiptMRead struct {
-	User map[string]FederationReceiptData `json:"m.read"`
-}
-
-type FederationReceiptData struct {
-	Data     ReceiptTS `json:"data"`
-	EventIDs []string  `json:"event_ids"`
+// OutputCrossSigningKeyUpdate is an entry in the signing key update output kafka log
+type OutputCrossSigningKeyUpdate struct {
+	CrossSigningKeyUpdate `json:"signing_keys"`
 }

eduserver/api/types.go

@@ -0,0 +1,59 @@
+// Copyright 2021 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.
+
+package api
+
+import "github.com/matrix-org/gomatrixserverlib"
+
+const (
+	MSigningKeyUpdate = "m.signing_key_update"
+)
+
+type TypingEvent struct {
+	Type   string `json:"type"`
+	RoomID string `json:"room_id"`
+	UserID string `json:"user_id"`
+	Typing bool   `json:"typing"`
+}
+
+type ReceiptEvent struct {
+	UserID    string                      `json:"user_id"`
+	RoomID    string                      `json:"room_id"`
+	EventID   string                      `json:"event_id"`
+	Type      string                      `json:"type"`
+	Timestamp gomatrixserverlib.Timestamp `json:"timestamp"`
+}
+
+type FederationReceiptMRead struct {
+	User map[string]FederationReceiptData `json:"m.read"`
+}
+
+type FederationReceiptData struct {
+	Data     ReceiptTS `json:"data"`
+	EventIDs []string  `json:"event_ids"`
+}
+
+type ReceiptMRead struct {
+	User map[string]ReceiptTS `json:"m.read"`
+}
+
+type ReceiptTS struct {
+	TS gomatrixserverlib.Timestamp `json:"ts"`
+}
+
+type CrossSigningKeyUpdate struct {
+	MasterKey      *gomatrixserverlib.CrossSigningKey `json:"master_key,omitempty"`
+	SelfSigningKey *gomatrixserverlib.CrossSigningKey `json:"self_signing_key,omitempty"`
+	UserID         string                             `json:"user_id"`
+}

eduserver/eduserver.go

@@ -52,6 +52,7 @@ func NewInternalAPI(
 		OutputTypingEventTopic:       cfg.Matrix.Kafka.TopicFor(config.TopicOutputTypingEvent),
 		OutputSendToDeviceEventTopic: cfg.Matrix.Kafka.TopicFor(config.TopicOutputSendToDeviceEvent),
 		OutputReceiptEventTopic:      cfg.Matrix.Kafka.TopicFor(config.TopicOutputReceiptEvent),
+		OutputKeyChangeEventTopic:    cfg.Matrix.Kafka.TopicFor(config.TopicOutputKeyChangeEvent),
 		ServerName:                   cfg.Matrix.ServerName,
 	}
 }

eduserver/input/input.go

@@ -24,6 +24,7 @@ import (
 	"github.com/Shopify/sarama"
 	"github.com/matrix-org/dendrite/eduserver/api"
 	"github.com/matrix-org/dendrite/eduserver/cache"
+	keyapi "github.com/matrix-org/dendrite/keyserver/api"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/sirupsen/logrus"
@@ -39,6 +40,8 @@ type EDUServerInputAPI struct {
 	OutputSendToDeviceEventTopic string
 	// The kafka topic to output new receipt events to
 	OutputReceiptEventTopic string
+	// The kafka topic to output new key change events to
+	OutputKeyChangeEventTopic string
 	// kafka producer
 	Producer sarama.SyncProducer
 	// Internal user query API
@@ -77,6 +80,36 @@ func (t *EDUServerInputAPI) InputSendToDeviceEvent(
 	return t.sendToDeviceEvent(ise)
 }
 
+// InputCrossSigningKeyUpdate implements api.EDUServerInputAPI
+func (t *EDUServerInputAPI) InputCrossSigningKeyUpdate(
+	ctx context.Context,
+	request *api.InputCrossSigningKeyUpdateRequest,
+	response *api.InputCrossSigningKeyUpdateResponse,
+) error {
+	eventJSON, err := json.Marshal(&keyapi.DeviceMessage{
+		Type: keyapi.TypeCrossSigningUpdate,
+		OutputCrossSigningKeyUpdate: &api.OutputCrossSigningKeyUpdate{
+			CrossSigningKeyUpdate: request.CrossSigningKeyUpdate,
+		},
+	})
+	if err != nil {
+		return err
+	}
+
+	logrus.WithFields(logrus.Fields{
+		"user_id": request.UserID,
+	}).Infof("Producing to topic '%s'", t.OutputKeyChangeEventTopic)
+
+	m := &sarama.ProducerMessage{
+		Topic: string(t.OutputKeyChangeEventTopic),
+		Key:   sarama.StringEncoder(request.UserID),
+		Value: sarama.ByteEncoder(eventJSON),
+	}
+
+	_, _, err = t.Producer.SendMessage(m)
+	return err
+}
+
 func (t *EDUServerInputAPI) sendTypingEvent(ite *api.InputTypingEvent) error {
 	ev := &api.TypingEvent{
 		Type:   gomatrixserverlib.MTyping,

eduserver/inthttp/client.go

@@ -15,6 +15,7 @@ const (
 	EDUServerInputTypingEventPath           = "/eduserver/input"
 	EDUServerInputSendToDeviceEventPath     = "/eduserver/sendToDevice"
 	EDUServerInputReceiptEventPath          = "/eduserver/receipt"
+	EDUServerInputCrossSigningKeyUpdatePath = "/eduserver/crossSigningKeyUpdate"
 )
 
 // NewEDUServerClient creates a EDUServerInputAPI implemented by talking to a HTTP POST API.
@@ -68,3 +69,16 @@ func (h *httpEDUServerInputAPI) InputReceiptEvent(
 	apiURL := h.eduServerURL + EDUServerInputReceiptEventPath
 	return httputil.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
 }
+
+// InputCrossSigningKeyUpdate implements EDUServerInputAPI
+func (h *httpEDUServerInputAPI) InputCrossSigningKeyUpdate(
+	ctx context.Context,
+	request *api.InputCrossSigningKeyUpdateRequest,
+	response *api.InputCrossSigningKeyUpdateResponse,
+) error {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "InputCrossSigningKeyUpdate")
+	defer span.Finish()
+
+	apiURL := h.eduServerURL + EDUServerInputCrossSigningKeyUpdatePath
+	return httputil.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+}

eduserver/inthttp/server.go

@@ -51,4 +51,17 @@ func AddRoutes(t api.EDUServerInputAPI, internalAPIMux *mux.Router) {
 			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
 		}),
 	)
+	internalAPIMux.Handle(EDUServerInputCrossSigningKeyUpdatePath,
+		httputil.MakeInternalAPI("inputCrossSigningKeyUpdate", func(req *http.Request) util.JSONResponse {
+			var request api.InputCrossSigningKeyUpdateRequest
+			var response api.InputCrossSigningKeyUpdateResponse
+			if err := json.NewDecoder(req.Body).Decode(&request); err != nil {
+				return util.MessageResponse(http.StatusBadRequest, err.Error())
+			}
+			if err := t.InputCrossSigningKeyUpdate(req.Context(), &request, &response); err != nil {
+				return util.ErrorResponse(err)
+			}
+			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
+		}),
+	)
 }

federationapi/routing/send.go

@@ -502,6 +502,22 @@ func (t *txnReq) processEDUs(ctx context.Context) {
 					}
 				}
 			}
+		case eduserverAPI.MSigningKeyUpdate:
+			var updatePayload eduserverAPI.CrossSigningKeyUpdate
+			if err := json.Unmarshal(e.Content, &updatePayload); err != nil {
+				util.GetLogger(ctx).WithError(err).WithFields(logrus.Fields{
+					"user_id": updatePayload.UserID,
+				}).Error("Failed to send signing key update to edu server")
+				continue
+			}
+			inputReq := &eduserverAPI.InputCrossSigningKeyUpdateRequest{
+				CrossSigningKeyUpdate: updatePayload,
+			}
+			inputRes := &eduserverAPI.InputCrossSigningKeyUpdateResponse{}
+			if err := t.eduAPI.InputCrossSigningKeyUpdate(ctx, inputReq, inputRes); err != nil {
+				util.GetLogger(ctx).WithError(err).Error("Failed to unmarshal cross-signing update")
+				continue
+			}
 		default:
 			util.GetLogger(ctx).WithField("type", e.Type).Debug("Unhandled EDU")
 		}

federationapi/routing/send_test.go

@@ -84,6 +84,14 @@ func (o *testEDUProducer) InputReceiptEvent(
 	return nil
 }
 
+func (o *testEDUProducer) InputCrossSigningKeyUpdate(
+	ctx context.Context,
+	request *eduAPI.InputCrossSigningKeyUpdateRequest,
+	response *eduAPI.InputCrossSigningKeyUpdateResponse,
+) error {
+	return nil
+}
+
 type testRoomserverAPI struct {
 	api.RoomserverInternalAPITrace
 	inputRoomEvents            []api.InputRoomEvent

federationsender/consumers/keychange.go

@@ -20,6 +20,7 @@ import (
 	"fmt"
 
 	"github.com/Shopify/sarama"
+	eduserverAPI "github.com/matrix-org/dendrite/eduserver/api"
 	"github.com/matrix-org/dendrite/federationsender/queue"
 	"github.com/matrix-org/dendrite/federationsender/storage"
 	"github.com/matrix-org/dendrite/internal"
@@ -28,6 +29,7 @@ import (
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dendrite/setup/process"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -83,6 +85,17 @@ func (t *KeyChangeConsumer) onMessage(msg *sarama.ConsumerMessage) error {
 		log.WithError(err).Errorf("failed to read device message from key change topic")
 		return nil
 	}
+	switch m.Type {
+	case api.TypeCrossSigningUpdate:
+		return t.onCrossSigningMessage(m)
+	case api.TypeDeviceKeyUpdate:
+		fallthrough
+	default:
+		return t.onDeviceKeyMessage(m)
+	}
+}
+
+func (t *KeyChangeConsumer) onDeviceKeyMessage(m api.DeviceMessage) error {
 	logger := log.WithField("user_id", m.UserID)
 
 	// only send key change events which originated from us
@@ -133,6 +146,50 @@ func (t *KeyChangeConsumer) onMessage(msg *sarama.ConsumerMessage) error {
 	return t.queues.SendEDU(edu, t.serverName, destinations)
 }
 
+func (t *KeyChangeConsumer) onCrossSigningMessage(m api.DeviceMessage) error {
+	output := m.CrossSigningKeyUpdate
+	_, host, err := gomatrixserverlib.SplitID('@', output.UserID)
+	if err != nil {
+		logrus.WithError(err).Errorf("fedsender key change consumer: user ID parse failure")
+		return nil
+	}
+	if host != gomatrixserverlib.ServerName(t.serverName) {
+		// Ignore any messages that didn't originate locally, otherwise we'll
+		// end up parroting information we received from other servers.
+		return nil
+	}
+	logger := log.WithField("user_id", output.UserID)
+
+	var queryRes roomserverAPI.QueryRoomsForUserResponse
+	err = t.rsAPI.QueryRoomsForUser(context.Background(), &roomserverAPI.QueryRoomsForUserRequest{
+		UserID:         output.UserID,
+		WantMembership: "join",
+	}, &queryRes)
+	if err != nil {
+		logger.WithError(err).Error("fedsender key change consumer: failed to calculate joined rooms for user")
+		return nil
+	}
+	// send this key change to all servers who share rooms with this user.
+	destinations, err := t.db.GetJoinedHostsForRooms(context.Background(), queryRes.RoomIDs)
+	if err != nil {
+		logger.WithError(err).Error("fedsender key change consumer: failed to calculate joined hosts for rooms user is in")
+		return nil
+	}
+
+	// Pack the EDU and marshal it
+	edu := &gomatrixserverlib.EDU{
+		Type:   eduserverAPI.MSigningKeyUpdate,
+		Origin: string(t.serverName),
+	}
+	if edu.Content, err = json.Marshal(output); err != nil {
+		logger.WithError(err).Error("fedsender key change consumer: failed to marshal output, dropping")
+		return nil
+	}
+
+	logger.Infof("Sending cross-signing update message to %q", destinations)
+	return t.queues.SendEDU(edu, t.serverName, destinations)
+}
+
 func prevID(streamID int) []int {
 	if streamID <= 1 {
 		return nil

go.mod

@@ -31,7 +31,7 @@ require (
 	github.com/matrix-org/go-http-js-libp2p v0.0.0-20200518170932-783164aeeda4
 	github.com/matrix-org/go-sqlite3-js v0.0.0-20210709140738-b0d1ba599a6d
 	github.com/matrix-org/gomatrix v0.0.0-20210324163249-be2af5ef2e16
-	github.com/matrix-org/gomatrixserverlib v0.0.0-20210809130922-d9c3f400582b
+	github.com/matrix-org/gomatrixserverlib v0.0.0-20210817115641-f9416ac1a723
 	github.com/matrix-org/naffka v0.0.0-20210623111924-14ff508b58e0
 	github.com/matrix-org/pinecone v0.0.0-20210623102758-74f885644c1b
 	github.com/matrix-org/util v0.0.0-20200807132607-55161520e1d4

go.sum

@@ -994,8 +994,8 @@ github.com/matrix-org/go-sqlite3-js v0.0.0-20210709140738-b0d1ba599a6d/go.mod h1
 github.com/matrix-org/gomatrix v0.0.0-20190528120928-7df988a63f26/go.mod h1:3fxX6gUjWyI/2Bt7J1OLhpCzOfO/bB3AiX0cJtEKud0=
 github.com/matrix-org/gomatrix v0.0.0-20210324163249-be2af5ef2e16 h1:ZtO5uywdd5dLDCud4r0r55eP4j9FuUNpl60Gmntcop4=
 github.com/matrix-org/gomatrix v0.0.0-20210324163249-be2af5ef2e16/go.mod h1:/gBX06Kw0exX1HrwmoBibFA98yBk/jxKpGVeyQbff+s=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20210809130922-d9c3f400582b h1:8St1B8QmlvMLsOmGqW3++0akUs0250IAi+AGcr5faxw=
-github.com/matrix-org/gomatrixserverlib v0.0.0-20210809130922-d9c3f400582b/go.mod h1:JsAzE1Ll3+gDWS9JSUHPJiiyAksvOOnGWF2nXdg4ZzU=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20210817115641-f9416ac1a723 h1:b8cyR4aYv9Lmf1lKgASJ+PFSp/GBv8ZFgb/O42ZXLGA=
+github.com/matrix-org/gomatrixserverlib v0.0.0-20210817115641-f9416ac1a723/go.mod h1:JsAzE1Ll3+gDWS9JSUHPJiiyAksvOOnGWF2nXdg4ZzU=
 github.com/matrix-org/naffka v0.0.0-20210623111924-14ff508b58e0 h1:HZCzy4oVzz55e+cOMiX/JtSF2UOY1evBl2raaE7ACcU=
 github.com/matrix-org/naffka v0.0.0-20210623111924-14ff508b58e0/go.mod h1:sjyPyRxKM5uw1nD2cJ6O2OxI6GOqyVBfNXqKjBZTBZE=
 github.com/matrix-org/pinecone v0.0.0-20210623102758-74f885644c1b h1:5X5vdWQ13xrNkJVqaJHPsrt7rKkMJH5iac0EtfOuxSg=

keyserver/api/api.go

@@ -20,6 +20,7 @@ import (
 	"strings"
 	"time"
 
+	eduapi "github.com/matrix-org/dendrite/eduserver/api"
 	"github.com/matrix-org/dendrite/keyserver/types"
 	userapi "github.com/matrix-org/dendrite/userapi/api"
 	"github.com/matrix-org/gomatrixserverlib"
@@ -47,6 +48,7 @@ type KeyError struct {
 	Err                string `json:"error"`
 	IsInvalidSignature bool   `json:"is_invalid_signature,omitempty"` // M_INVALID_SIGNATURE
 	IsMissingParam     bool   `json:"is_missing_param,omitempty"`     // M_MISSING_PARAM
+	IsInvalidParam     bool   `json:"is_invalid_param,omitempty"`     // M_INVALID_PARAM
 }
 
 func (k *KeyError) Error() string {
@@ -64,6 +66,7 @@ const (
 type DeviceMessage struct {
 	Type                                DeviceMessageType `json:"Type,omitempty"`
 	*DeviceKeys                         `json:"DeviceKeys,omitempty"`
+	*eduapi.OutputCrossSigningKeyUpdate `json:"CrossSigningKeyUpdate,omitempty"`
 	// A monotonically increasing number which represents device changes for this user.
 	StreamID int
 }

keyserver/consumers/cross_signing.go

@@ -0,0 +1,112 @@
+// Copyright 2021 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.
+
+package consumers
+
+import (
+	"context"
+	"encoding/json"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/keyserver/api"
+	"github.com/matrix-org/dendrite/keyserver/storage"
+	"github.com/matrix-org/dendrite/setup/config"
+	"github.com/matrix-org/dendrite/setup/process"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+
+	"github.com/Shopify/sarama"
+)
+
+type OutputCrossSigningKeyUpdateConsumer struct {
+	eduServerConsumer *internal.ContinualConsumer
+	keyDB             storage.Database
+	keyAPI            api.KeyInternalAPI
+	serverName        string
+}
+
+func NewOutputCrossSigningKeyUpdateConsumer(
+	process *process.ProcessContext,
+	cfg *config.Dendrite,
+	kafkaConsumer sarama.Consumer,
+	keyDB storage.Database,
+	keyAPI api.KeyInternalAPI,
+) *OutputCrossSigningKeyUpdateConsumer {
+	// The keyserver both produces and consumes on the TopicOutputKeyChangeEvent
+	// topic. We will only produce events where the UserID matches our server name,
+	// and we will only consume events where the UserID does NOT match our server
+	// name (because the update came from a remote server).
+	consumer := internal.ContinualConsumer{
+		Process:        process,
+		ComponentName:  "keyserver/keyserver",
+		Topic:          cfg.Global.Kafka.TopicFor(config.TopicOutputKeyChangeEvent),
+		Consumer:       kafkaConsumer,
+		PartitionStore: keyDB,
+	}
+	s := &OutputCrossSigningKeyUpdateConsumer{
+		eduServerConsumer: &consumer,
+		keyDB:             keyDB,
+		keyAPI:            keyAPI,
+		serverName:        string(cfg.Global.ServerName),
+	}
+	consumer.ProcessMessage = s.onMessage
+
+	return s
+}
+
+func (s *OutputCrossSigningKeyUpdateConsumer) Start() error {
+	return s.eduServerConsumer.Start()
+}
+
+// onMessage is called in response to a message received on the
+// key change events topic from the key server.
+func (t *OutputCrossSigningKeyUpdateConsumer) onMessage(msg *sarama.ConsumerMessage) error {
+	var m api.DeviceMessage
+	if err := json.Unmarshal(msg.Value, &m); err != nil {
+		logrus.WithError(err).Errorf("failed to read device message from key change topic")
+		return nil
+	}
+	switch m.Type {
+	case api.TypeCrossSigningUpdate:
+		return t.onCrossSigningMessage(m)
+	default:
+		return nil
+	}
+}
+
+func (s *OutputCrossSigningKeyUpdateConsumer) onCrossSigningMessage(m api.DeviceMessage) error {
+	output := m.CrossSigningKeyUpdate
+	_, host, err := gomatrixserverlib.SplitID('@', output.UserID)
+	if err != nil {
+		logrus.WithError(err).Errorf("eduserver output log: user ID parse failure")
+		return nil
+	}
+	if host == gomatrixserverlib.ServerName(s.serverName) {
+		// Ignore any messages that contain information about our own users, as
+		// they already originated from this server.
+		return nil
+	}
+	uploadReq := &api.PerformUploadDeviceKeysRequest{
+		UserID: output.UserID,
+	}
+	if output.MasterKey != nil {
+		uploadReq.MasterKey = *output.MasterKey
+	}
+	if output.SelfSigningKey != nil {
+		uploadReq.SelfSigningKey = *output.SelfSigningKey
+	}
+	uploadRes := &api.PerformUploadDeviceKeysResponse{}
+	s.keyAPI.PerformUploadDeviceKeys(context.TODO(), uploadReq, uploadRes)
+	return uploadRes.Error
+}

keyserver/consumers/eduserver.go

@@ -1,61 +0,0 @@
-package consumers
-
-import (
-	"fmt"
-
-	"github.com/matrix-org/dendrite/internal"
-	"github.com/matrix-org/dendrite/keyserver/api"
-	"github.com/matrix-org/dendrite/keyserver/storage"
-	"github.com/matrix-org/dendrite/setup/config"
-	"github.com/matrix-org/dendrite/setup/process"
-
-	"github.com/Shopify/sarama"
-)
-
-type OutputSigningKeyUpdateConsumer struct {
-	eduServerConsumer *internal.ContinualConsumer
-	keyDB             storage.Database
-	keyAPI            api.KeyInternalAPI
-	serverName        string
-}
-
-func NewOutputSigningKeyUpdateConsumer(
-	process *process.ProcessContext,
-	cfg *config.Dendrite,
-	kafkaConsumer sarama.Consumer,
-	keyDB storage.Database,
-	keyAPI api.KeyInternalAPI,
-) *OutputSigningKeyUpdateConsumer {
-	consumer := internal.ContinualConsumer{
-		Process:        process,
-		ComponentName:  "keyserver/eduserver",
-		Topic:          cfg.Global.Kafka.TopicFor(config.TopicOutputSigningKeyUpdate),
-		Consumer:       kafkaConsumer,
-		PartitionStore: keyDB,
-	}
-	s := &OutputSigningKeyUpdateConsumer{
-		eduServerConsumer: &consumer,
-		keyDB:             keyDB,
-		keyAPI:            keyAPI,
-		serverName:        string(cfg.Global.ServerName),
-	}
-	consumer.ProcessMessage = s.onMessage
-
-	return s
-}
-
-func (s *OutputSigningKeyUpdateConsumer) Start() error {
-	return s.eduServerConsumer.Start()
-}
-
-func (s *OutputSigningKeyUpdateConsumer) onMessage(msg *sarama.ConsumerMessage) error {
-	/*
-		var output eduapi.OutputSigningKeyUpdate
-		if err := json.Unmarshal(msg.Value, &output); err != nil {
-			log.WithError(err).Errorf("eduserver output log: message parse failure")
-			return nil
-		}
-		return nil
-	*/
-	return fmt.Errorf("TODO")
-}

keyserver/internal/cross_signing.go

@@ -19,14 +19,15 @@ import (
 	"context"
 	"crypto/ed25519"
 	"database/sql"
-	"encoding/json"
 	"fmt"
 	"strings"
 
+	eduserverAPI "github.com/matrix-org/dendrite/eduserver/api"
 	"github.com/matrix-org/dendrite/keyserver/api"
 	"github.com/matrix-org/dendrite/keyserver/types"
 	"github.com/matrix-org/gomatrixserverlib"
 	"github.com/sirupsen/logrus"
+	"golang.org/x/crypto/curve25519"
 )
 
 func sanityCheckKey(key gomatrixserverlib.CrossSigningKey, userID string, purpose gomatrixserverlib.CrossSigningKeyPurpose) error {
@@ -45,6 +46,41 @@ func sanityCheckKey(key gomatrixserverlib.CrossSigningKey, userID string, purpos
 		if tokens[1] != b64 {
 			return fmt.Errorf("key ID isn't correct")
 		}
+		switch tokens[0] {
+		case "ed25519":
+			if len(keyData) != ed25519.PublicKeySize {
+				return fmt.Errorf("ed25519 key is not the correct length")
+			}
+		case "curve25519":
+			if len(keyData) != curve25519.PointSize {
+				return fmt.Errorf("curve25519 key is not the correct length")
+			}
+		default:
+			// We can't enforce the key length to be correct for an
+			// algorithm that we don't recognise, so instead we'll
+			// just make sure that it isn't incredibly excessive.
+			if l := len(keyData); l > 4096 {
+				return fmt.Errorf("unknown key type is too long (%d bytes)", l)
+			}
+		}
+	}
+
+	// Check to see if the signatures make sense
+	for _, forOriginUser := range key.Signatures {
+		for originKeyID, originSignature := range forOriginUser {
+			switch strings.SplitN(string(originKeyID), ":", 1)[0] {
+			case "ed25519":
+				if len(originSignature) != ed25519.SignatureSize {
+					return fmt.Errorf("ed25519 signature is not the correct length")
+				}
+			case "curve25519":
+				return fmt.Errorf("curve25519 signatures are impossible")
+			default:
+				if l := len(originSignature); l > 4096 {
+					return fmt.Errorf("unknown signature type is too long (%d bytes)", l)
+				}
+			}
+		}
 	}
 
 	// Does the key claim to be from the right user?
@@ -69,42 +105,68 @@ func sanityCheckKey(key gomatrixserverlib.CrossSigningKey, userID string, purpos
 
 // nolint:gocyclo
 func (a *KeyInternalAPI) PerformUploadDeviceKeys(ctx context.Context, req *api.PerformUploadDeviceKeysRequest, res *api.PerformUploadDeviceKeysResponse) {
-	var masterKey gomatrixserverlib.Base64Bytes
+	// Find the keys to store.
+	byPurpose := map[gomatrixserverlib.CrossSigningKeyPurpose]gomatrixserverlib.CrossSigningKey{}
+	toStore := types.CrossSigningKeyMap{}
 	hasMasterKey := false
 
 	if len(req.MasterKey.Keys) > 0 {
 		if err := sanityCheckKey(req.MasterKey, req.UserID, gomatrixserverlib.CrossSigningKeyPurposeMaster); err != nil {
 			res.Error = &api.KeyError{
 				Err:            "Master key sanity check failed: " + err.Error(),
+				IsInvalidParam: true,
 			}
 			return
 		}
-		for _, keyData := range req.MasterKey.Keys { // iterates once, because sanityCheckKey requires one key
-			hasMasterKey = true
-			masterKey = keyData
+
+		byPurpose[gomatrixserverlib.CrossSigningKeyPurposeMaster] = req.MasterKey
+		for _, key := range req.MasterKey.Keys { // iterates once, see sanityCheckKey
+			toStore[gomatrixserverlib.CrossSigningKeyPurposeMaster] = key
 		}
+		hasMasterKey = true
 	}
 
 	if len(req.SelfSigningKey.Keys) > 0 {
 		if err := sanityCheckKey(req.SelfSigningKey, req.UserID, gomatrixserverlib.CrossSigningKeyPurposeSelfSigning); err != nil {
 			res.Error = &api.KeyError{
 				Err:            "Self-signing key sanity check failed: " + err.Error(),
+				IsInvalidParam: true,
 			}
 			return
 		}
+
+		byPurpose[gomatrixserverlib.CrossSigningKeyPurposeSelfSigning] = req.SelfSigningKey
+		for _, key := range req.SelfSigningKey.Keys { // iterates once, see sanityCheckKey
+			toStore[gomatrixserverlib.CrossSigningKeyPurposeSelfSigning] = key
+		}
 	}
 
 	if len(req.UserSigningKey.Keys) > 0 {
 		if err := sanityCheckKey(req.UserSigningKey, req.UserID, gomatrixserverlib.CrossSigningKeyPurposeUserSigning); err != nil {
 			res.Error = &api.KeyError{
 				Err:            "User-signing key sanity check failed: " + err.Error(),
+				IsInvalidParam: true,
 			}
 			return
 		}
+
+		byPurpose[gomatrixserverlib.CrossSigningKeyPurposeUserSigning] = req.UserSigningKey
+		for _, key := range req.UserSigningKey.Keys { // iterates once, see sanityCheckKey
+			toStore[gomatrixserverlib.CrossSigningKeyPurposeUserSigning] = key
+		}
 	}
 
-	// If the user hasn't given a new master key, then let's go and get their
-	// existing keys from the database.
+	// If there's nothing to do then stop here.
+	if len(toStore) == 0 {
+		res.Error = &api.KeyError{
+			Err:            "No keys were supplied in the request",
+			IsMissingParam: true,
+		}
+		return
+	}
+
+	// We can't have a self-signing or user-signing key without a master
+	// key, so make sure we have one of those.
 	if !hasMasterKey {
 		existingKeys, err := a.DB.CrossSigningKeysDataForUser(ctx, req.UserID)
 		if err != nil {
@@ -114,87 +176,20 @@ func (a *KeyInternalAPI) PerformUploadDeviceKeys(ctx context.Context, req *api.P
 			return
 		}
 
-		masterKey, hasMasterKey = existingKeys[gomatrixserverlib.CrossSigningKeyPurposeMaster]
+		_, hasMasterKey = existingKeys[gomatrixserverlib.CrossSigningKeyPurposeMaster]
 	}
 
-	// If we still don't have a master key at this point then there's nothing else
-	// we can do - we've checked both the request and the database.
+	// If we still can't find a master key for the user then stop the upload.
+	// This satisfies the "Fails to upload self-signing key without master key" test.
 	if !hasMasterKey {
 		res.Error = &api.KeyError{
-			Err:            "No master key was found either in the database or in the request!",
-			IsMissingParam: true,
-		}
-		return
-	}
-
-	// The key ID is basically the key itself.
-	masterKeyID := gomatrixserverlib.KeyID(fmt.Sprintf("ed25519:%s", masterKey.Encode()))
-
-	// Work out which things we need to verify the signatures for.
-	toVerify := make(map[gomatrixserverlib.CrossSigningKeyPurpose]gomatrixserverlib.CrossSigningKey, 3)
-	toStore := types.CrossSigningKeyMap{}
-	if len(req.MasterKey.Keys) > 0 {
-		toVerify[gomatrixserverlib.CrossSigningKeyPurposeMaster] = req.MasterKey
-	}
-	if len(req.SelfSigningKey.Keys) > 0 {
-		toVerify[gomatrixserverlib.CrossSigningKeyPurposeSelfSigning] = req.SelfSigningKey
-	}
-	if len(req.UserSigningKey.Keys) > 0 {
-		toVerify[gomatrixserverlib.CrossSigningKeyPurposeUserSigning] = req.UserSigningKey
-	}
-
-	if len(toVerify) == 0 {
-		res.Error = &api.KeyError{
-			Err:            "No supplied keys available for verification",
-			IsMissingParam: true,
-		}
-		return
-	}
-
-	for purpose, key := range toVerify {
-		// Collect together the key IDs we need to verify with. This will include
-		// all of the key IDs specified in the signatures.
-		keyJSON, err := json.Marshal(key)
-		if err != nil {
-			res.Error = &api.KeyError{
-				Err: fmt.Sprintf("The JSON of the key section is invalid: %s", err.Error()),
-			}
-			return
-		}
-
-		switch purpose {
-		case gomatrixserverlib.CrossSigningKeyPurposeMaster:
-			// The master key might have a signature attached to it from the
-			// previous key, or from a device key, but there's no real need
-			// to verify it. Clients will perform key checks when the master
-			// key changes.
-
-		default:
-			// Sub-keys should be signed by the master key.
-			if err := gomatrixserverlib.VerifyJSON(req.UserID, masterKeyID, ed25519.PublicKey(masterKey), keyJSON); err != nil {
-				res.Error = &api.KeyError{
-					Err:                fmt.Sprintf("The %q sub-key failed master key signature verification: %s", purpose, err.Error()),
-					IsInvalidSignature: true,
-				}
-				return
-			}
-		}
-
-		// If we've reached this point then all the signatures are valid so
-		// add the key to the list of keys to store.
-		for _, keyData := range key.Keys { // iterates once, see sanityCheckKey
-			toStore[purpose] = keyData
-		}
-	}
-
-	if len(toStore) == 0 {
-		res.Error = &api.KeyError{
-			Err:            "No supplied keys passed verification",
+			Err:            "No master key was found",
 			IsMissingParam: true,
 		}
 		return
 	}
 
+	// Store the keys.
 	if err := a.DB.StoreCrossSigningKeysForUser(ctx, req.UserID, toStore); err != nil {
 		res.Error = &api.KeyError{
 			Err: fmt.Sprintf("a.DB.StoreCrossSigningKeysForUser: %s", err),
@@ -203,7 +198,7 @@ func (a *KeyInternalAPI) PerformUploadDeviceKeys(ctx context.Context, req *api.P
 	}
 
 	// Now upload any signatures that were included with the keys.
-	for _, key := range toVerify {
+	for _, key := range byPurpose {
 		var targetKeyID gomatrixserverlib.KeyID
 		for targetKey := range key.Keys { // iterates once, see sanityCheckKey
 			targetKeyID = targetKey
@@ -222,6 +217,28 @@ func (a *KeyInternalAPI) PerformUploadDeviceKeys(ctx context.Context, req *api.P
 			}
 		}
 	}
+
+	// Finally, generate a notification that we updated the keys.
+	if _, host, err := gomatrixserverlib.SplitID('@', req.UserID); err == nil && host == a.ThisServer {
+		update := eduserverAPI.CrossSigningKeyUpdate{
+			UserID: req.UserID,
+		}
+		if mk, ok := byPurpose[gomatrixserverlib.CrossSigningKeyPurposeMaster]; ok {
+			update.MasterKey = &mk
+		}
+		if ssk, ok := byPurpose[gomatrixserverlib.CrossSigningKeyPurposeSelfSigning]; ok {
+			update.SelfSigningKey = &ssk
+		}
+		if update.MasterKey == nil && update.SelfSigningKey == nil {
+			return
+		}
+		if err := a.Producer.ProduceSigningKeyUpdate(update); err != nil {
+			res.Error = &api.KeyError{
+				Err: fmt.Sprintf("a.Producer.ProduceSigningKeyUpdate: %s", err),
+			}
+			return
+		}
+	}
 }
 
 func (a *KeyInternalAPI) PerformUploadDeviceSignatures(ctx context.Context, req *api.PerformUploadDeviceSignaturesRequest, res *api.PerformUploadDeviceSignaturesResponse) {
@@ -277,7 +294,7 @@ func (a *KeyInternalAPI) PerformUploadDeviceSignatures(ctx context.Context, req
 		}
 	}
 
-	if err := a.processSelfSignatures(ctx, req.UserID, queryRes, selfSignatures); err != nil {
+	if err := a.processSelfSignatures(ctx, selfSignatures); err != nil {
 		res.Error = &api.KeyError{
 			Err: fmt.Sprintf("a.processSelfSignatures: %s", err),
 		}
@@ -290,10 +307,25 @@ func (a *KeyInternalAPI) PerformUploadDeviceSignatures(ctx context.Context, req
 		}
 		return
 	}
+
+	// Finally, generate a notification that we updated the signatures.
+	for userID := range req.Signatures {
+		if _, host, err := gomatrixserverlib.SplitID('@', userID); err == nil && host == a.ThisServer {
+			update := eduserverAPI.CrossSigningKeyUpdate{
+				UserID: userID,
+			}
+			if err := a.Producer.ProduceSigningKeyUpdate(update); err != nil {
+				res.Error = &api.KeyError{
+					Err: fmt.Sprintf("a.Producer.ProduceSigningKeyUpdate: %s", err),
+				}
+				return
+			}
+		}
+	}
 }
 
 func (a *KeyInternalAPI) processSelfSignatures(
-	ctx context.Context, _ string, queryRes *api.QueryKeysResponse,
+	ctx context.Context,
 	signatures map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice,
 ) error {
 	// Here we will process:
@@ -304,37 +336,8 @@ func (a *KeyInternalAPI) processSelfSignatures(
 		for targetKeyID, signature := range forTargetUserID {
 			switch sig := signature.CrossSigningBody.(type) {
 			case *gomatrixserverlib.CrossSigningKey:
-				// The user is signing their master key with one of their devices
-				// The QueryKeys response should contain the device key hopefully.
-				// First we need to marshal the blob back into JSON so we can verify
-				// it.
-				j, err := json.Marshal(sig)
-				if err != nil {
-					return fmt.Errorf("json.Marshal: %w", err)
-				}
-
 				for originUserID, forOriginUserID := range sig.Signatures {
-					originDeviceKeys, ok := queryRes.DeviceKeys[originUserID]
-					if !ok {
-						return fmt.Errorf("missing device keys for user %q", originUserID)
-					}
-
 					for originKeyID, originSig := range forOriginUserID {
-						var originKey gomatrixserverlib.DeviceKeys
-						if err := json.Unmarshal(originDeviceKeys[string(originKeyID)], &originKey); err != nil {
-							return fmt.Errorf("json.Unmarshal: %w", err)
-						}
-
-						originSigningKey, ok := originKey.Keys[originKeyID]
-						if !ok {
-							return fmt.Errorf("missing origin signing key %q", originKeyID)
-						}
-						originSigningKeyPublic := ed25519.PublicKey(originSigningKey)
-
-						if err := gomatrixserverlib.VerifyJSON(originUserID, originKeyID, originSigningKeyPublic, j); err != nil {
-							return fmt.Errorf("gomatrixserverlib.VerifyJSON: %w", err)
-						}
-
 						if err := a.DB.StoreCrossSigningSigsForTarget(
 							ctx, originUserID, originKeyID, targetUserID, targetKeyID, originSig,
 						); err != nil {
@@ -344,35 +347,8 @@ func (a *KeyInternalAPI) processSelfSignatures(
 				}
 
 			case *gomatrixserverlib.DeviceKeys:
-				// The user is signing one of their devices with their self-signing key
-				// The QueryKeys response should contain the master key hopefully.
-				// First we need to marshal the blob back into JSON so we can verify
-				// it.
-				j, err := json.Marshal(sig)
-				if err != nil {
-					return fmt.Errorf("json.Marshal: %w", err)
-				}
-
 				for originUserID, forOriginUserID := range sig.Signatures {
 					for originKeyID, originSig := range forOriginUserID {
-						originSelfSigningKeys, ok := queryRes.SelfSigningKeys[originUserID]
-						if !ok {
-							return fmt.Errorf("missing self-signing key for user %q", originUserID)
-						}
-
-						var originSelfSigningKeyID gomatrixserverlib.KeyID
-						var originSelfSigningKey gomatrixserverlib.Base64Bytes
-						for keyID, key := range originSelfSigningKeys.Keys {
-							originSelfSigningKeyID, originSelfSigningKey = keyID, key
-							break
-						}
-
-						originSelfSigningKeyPublic := ed25519.PublicKey(originSelfSigningKey)
-
-						if err := gomatrixserverlib.VerifyJSON(originUserID, originSelfSigningKeyID, originSelfSigningKeyPublic, j); err != nil {
-							return fmt.Errorf("gomatrixserverlib.VerifyJSON: %w", err)
-						}
-
 						if err := a.DB.StoreCrossSigningSigsForTarget(
 							ctx, originUserID, originKeyID, targetUserID, targetKeyID, originSig,
 						); err != nil {

keyserver/keyserver.go

@@ -65,7 +65,7 @@ func NewInternalAPI(
 		}
 	}()
 
-	keyconsumer := consumers.NewOutputSigningKeyUpdateConsumer(
+	keyconsumer := consumers.NewOutputCrossSigningKeyUpdateConsumer(
 		base.ProcessContext, base.Cfg, consumer, db, ap,
 	)
 	if err := keyconsumer.Start(); err != nil {

keyserver/producers/keychange.go

@@ -19,6 +19,7 @@ import (
 	"encoding/json"
 
 	"github.com/Shopify/sarama"
+	eduapi "github.com/matrix-org/dendrite/eduserver/api"
 	"github.com/matrix-org/dendrite/keyserver/api"
 	"github.com/matrix-org/dendrite/keyserver/storage"
 	"github.com/sirupsen/logrus"
@@ -73,3 +74,36 @@ func (p *KeyChange) ProduceKeyChanges(keys []api.DeviceMessage) error {
 	}
 	return nil
 }
+
+func (p *KeyChange) ProduceSigningKeyUpdate(key eduapi.CrossSigningKeyUpdate) error {
+	var m sarama.ProducerMessage
+	output := &api.DeviceMessage{
+		Type: api.TypeCrossSigningUpdate,
+		OutputCrossSigningKeyUpdate: &eduapi.OutputCrossSigningKeyUpdate{
+			CrossSigningKeyUpdate: key,
+		},
+	}
+
+	value, err := json.Marshal(output)
+	if err != nil {
+		return err
+	}
+
+	m.Topic = string(p.Topic)
+	m.Key = sarama.StringEncoder(key.UserID)
+	m.Value = sarama.ByteEncoder(value)
+
+	partition, offset, err := p.Producer.SendMessage(&m)
+	if err != nil {
+		return err
+	}
+	err = p.DB.StoreKeyChange(context.Background(), partition, offset, key.UserID)
+	if err != nil {
+		return err
+	}
+
+	logrus.WithFields(logrus.Fields{
+		"user_id": key.UserID,
+	}).Infof("Produced to cross-signing update topic '%s'", p.Topic)
+	return nil
+}

setup/config/config_kafka.go

@@ -10,7 +10,6 @@ const (
 	TopicOutputRoomEvent         = "OutputRoomEvent"
 	TopicOutputClientData        = "OutputClientData"
 	TopicOutputReceiptEvent      = "OutputReceiptEvent"
-	TopicOutputSigningKeyUpdate  = "OutputSigningKeyUpdate"
 )
 
 type Kafka struct {

syncapi/consumers/keychange.go

@@ -29,6 +29,7 @@ import (
 	"github.com/matrix-org/dendrite/syncapi/storage"
 	"github.com/matrix-org/dendrite/syncapi/types"
 	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
 	log "github.com/sirupsen/logrus"
 )
 
@@ -104,13 +105,23 @@ func (s *OutputKeyChangeEventConsumer) updateOffset(msg *sarama.ConsumerMessage)
 func (s *OutputKeyChangeEventConsumer) onMessage(msg *sarama.ConsumerMessage) error {
 	defer s.updateOffset(msg)
 
-	var output api.DeviceMessage
-	if err := json.Unmarshal(msg.Value, &output); err != nil {
-		// If the message was invalid, log it and move on to the next message in the stream
-		log.WithError(err).Error("syncapi: failed to unmarshal key change event from key server")
-		sentry.CaptureException(err)
-		return err
+	var m api.DeviceMessage
+	if err := json.Unmarshal(msg.Value, &m); err != nil {
+		logrus.WithError(err).Errorf("failed to read device message from key change topic")
+		return nil
 	}
+	switch m.Type {
+	case api.TypeCrossSigningUpdate:
+		return s.onCrossSigningMessage(m, msg.Offset, msg.Partition)
+	case api.TypeDeviceKeyUpdate:
+		fallthrough
+	default:
+		return s.onDeviceKeyMessage(m, msg.Offset, msg.Partition)
+	}
+}
+
+func (s *OutputKeyChangeEventConsumer) onDeviceKeyMessage(m api.DeviceMessage, offset int64, partition int32) error {
+	output := m.DeviceKeys
 	// work out who we need to notify about the new key
 	var queryRes roomserverAPI.QuerySharedUsersResponse
 	err := s.rsAPI.QuerySharedUsers(context.Background(), &roomserverAPI.QuerySharedUsersRequest{
@@ -124,8 +135,35 @@ func (s *OutputKeyChangeEventConsumer) onMessage(msg *sarama.ConsumerMessage) er
 	// make sure we get our own key updates too!
 	queryRes.UserIDsToCount[output.UserID] = 1
 	posUpdate := types.LogPosition{
-		Offset:    msg.Offset,
-		Partition: msg.Partition,
+		Offset:    offset,
+		Partition: partition,
+	}
+
+	s.stream.Advance(posUpdate)
+	for userID := range queryRes.UserIDsToCount {
+		s.notifier.OnNewKeyChange(types.StreamingToken{DeviceListPosition: posUpdate}, userID, output.UserID)
+	}
+
+	return nil
+}
+
+func (s *OutputKeyChangeEventConsumer) onCrossSigningMessage(m api.DeviceMessage, offset int64, partition int32) error {
+	output := m.CrossSigningKeyUpdate
+	// work out who we need to notify about the new key
+	var queryRes roomserverAPI.QuerySharedUsersResponse
+	err := s.rsAPI.QuerySharedUsers(context.Background(), &roomserverAPI.QuerySharedUsersRequest{
+		UserID: output.UserID,
+	}, &queryRes)
+	if err != nil {
+		log.WithError(err).Error("syncapi: failed to QuerySharedUsers for key change event from key server")
+		sentry.CaptureException(err)
+		return err
+	}
+	// make sure we get our own key updates too!
+	queryRes.UserIDsToCount[output.UserID] = 1
+	posUpdate := types.LogPosition{
+		Offset:    offset,
+		Partition: partition,
 	}
 
 	s.stream.Advance(posUpdate)

sytest-whitelist

@@ -554,3 +554,5 @@ Can upload self-signing keys
 Fails to upload self-signing keys with no auth
 Fails to upload self-signing key without master key
 can fetch self-signing keys over federation
+Changing master key notifies local users
+Changing user-signing key notifies local users