Cross-signing groundwork (#1953)

* Cross-signing groundwork

* Update to matrix-org/gomatrixserverlib#274

* Fix gobind builds, which stops unit tests in CI from yelling

* Some changes from review comments

* Fix build by passing in UIA

* Update to matrix-org/gomatrixserverlib@bec8d22

* Process master/self-signing keys from devices call

* nolint

* Enum-ify the key type in the database

* Process self-signing key too

* Fix sanity check in device list updater

* Fix check

* Fix sytest, hopefully

* Fix build

build/gobind-pinecone/monolith.go

@@ -299,7 +299,7 @@ func (m *DendriteMonolith) Start() {
 		base, federation, rsAPI, keyRing, true,
 	)
 
-	keyAPI := keyserver.NewInternalAPI(&base.Cfg.KeyServer, fsAPI)
+	keyAPI := keyserver.NewInternalAPI(base, &base.Cfg.KeyServer, fsAPI)
 	m.userAPI = userapi.NewInternalAPI(accountDB, &cfg.UserAPI, cfg.Derived.ApplicationServices, keyAPI)
 	keyAPI.SetUserAPI(m.userAPI)
 

build/gobind-yggdrasil/monolith.go

@@ -119,7 +119,7 @@ func (m *DendriteMonolith) Start() {
 		base, federation, rsAPI, keyRing, true,
 	)
 
-	keyAPI := keyserver.NewInternalAPI(&base.Cfg.KeyServer, federation)
+	keyAPI := keyserver.NewInternalAPI(base, &base.Cfg.KeyServer, federation)
 	userAPI := userapi.NewInternalAPI(accountDB, &cfg.UserAPI, cfg.Derived.ApplicationServices, keyAPI)
 	keyAPI.SetUserAPI(userAPI)
 

clientapi/auth/password.go

@@ -52,7 +52,7 @@ func (t *LoginTypePassword) Login(ctx context.Context, req interface{}) (*Login,
 	if username == "" {
 		return nil, &util.JSONResponse{
 			Code: http.StatusUnauthorized,
-			JSON: jsonerror.BadJSON("'user' must be supplied."),
+			JSON: jsonerror.BadJSON("A username must be supplied."),
 		}
 	}
 	localpart, err := userutil.ParseUsernameParam(username, &t.Config.Matrix.ServerName)
@@ -68,7 +68,7 @@ func (t *LoginTypePassword) Login(ctx context.Context, req interface{}) (*Login,
 		// but that would leak the existence of the user.
 		return nil, &util.JSONResponse{
 			Code: http.StatusForbidden,
-			JSON: jsonerror.Forbidden("username or password was incorrect, or the account does not exist"),
+			JSON: jsonerror.Forbidden("The username or password was incorrect or the account does not exist."),
 		}
 	}
 	return &r.Login, nil

clientapi/auth/user_interactive.go

@@ -220,7 +220,7 @@ func (u *UserInteractive) Verify(ctx context.Context, bodyBytes []byte, device *
 	if !ok {
 		return nil, &util.JSONResponse{
 			Code: http.StatusBadRequest,
-			JSON: jsonerror.BadJSON("unknown auth.type: " + authType),
+			JSON: jsonerror.BadJSON("Unknown auth.type: " + authType),
 		}
 	}
 
@@ -231,7 +231,7 @@ func (u *UserInteractive) Verify(ctx context.Context, bodyBytes []byte, device *
 		if !u.IsSingleStageFlow(authType) {
 			return nil, &util.JSONResponse{
 				Code: http.StatusBadRequest,
-				JSON: jsonerror.Unknown("missing or unknown auth.session"),
+				JSON: jsonerror.Unknown("The auth.session is missing or unknown."),
 			}
 		}
 	}

clientapi/jsonerror/jsonerror.go

@@ -125,6 +125,18 @@ func GuestAccessForbidden(msg string) *MatrixError {
 	return &MatrixError{"M_GUEST_ACCESS_FORBIDDEN", msg}
 }
 
+// InvalidSignature is an error which is returned when the client tries
+// to upload invalid signatures.
+func InvalidSignature(msg string) *MatrixError {
+	return &MatrixError{"M_INVALID_SIGNATURE", msg}
+}
+
+// MissingParam is an error that is returned when a parameter was incorrect,
+// traditionally with cross-signing.
+func MissingParam(msg string) *MatrixError {
+	return &MatrixError{"M_MISSING_PARAM", msg}
+}
+
 type IncompatibleRoomVersionError struct {
 	RoomVersion string `json:"room_version"`
 	Error       string `json:"error"`

clientapi/routing/key_crosssigning.go

@@ -0,0 +1,125 @@
+// 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 routing
+
+import (
+	"encoding/json"
+	"io/ioutil"
+	"net/http"
+
+	"github.com/matrix-org/dendrite/clientapi/auth"
+	"github.com/matrix-org/dendrite/clientapi/httputil"
+	"github.com/matrix-org/dendrite/clientapi/jsonerror"
+	"github.com/matrix-org/dendrite/keyserver/api"
+	"github.com/matrix-org/dendrite/setup/config"
+	userapi "github.com/matrix-org/dendrite/userapi/api"
+	"github.com/matrix-org/dendrite/userapi/storage/accounts"
+	"github.com/matrix-org/util"
+)
+
+func UploadCrossSigningDeviceKeys(
+	req *http.Request, userInteractiveAuth *auth.UserInteractive,
+	keyserverAPI api.KeyInternalAPI, device *userapi.Device,
+	accountDB accounts.Database, cfg *config.ClientAPI,
+) util.JSONResponse {
+	uploadReq := &api.PerformUploadDeviceKeysRequest{}
+	uploadRes := &api.PerformUploadDeviceKeysResponse{}
+
+	ctx := req.Context()
+	defer req.Body.Close() // nolint:errcheck
+	bodyBytes, err := ioutil.ReadAll(req.Body)
+	if err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON("The request body could not be read: " + err.Error()),
+		}
+	}
+
+	if _, err := userInteractiveAuth.Verify(ctx, bodyBytes, device); err != nil {
+		return *err
+	}
+
+	if err = json.Unmarshal(bodyBytes, &uploadReq); err != nil {
+		return util.JSONResponse{
+			Code: http.StatusBadRequest,
+			JSON: jsonerror.BadJSON("The request body could not be unmarshalled: " + err.Error()),
+		}
+	}
+
+	uploadReq.UserID = device.UserID
+	keyserverAPI.PerformUploadDeviceKeys(req.Context(), uploadReq, uploadRes)
+
+	if err := uploadRes.Error; err != nil {
+		switch {
+		case err.IsInvalidSignature:
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.InvalidSignature(err.Error()),
+			}
+		case err.IsMissingParam:
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.MissingParam(err.Error()),
+			}
+		default:
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.Unknown(err.Error()),
+			}
+		}
+	}
+
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		JSON: struct{}{},
+	}
+}
+
+func UploadCrossSigningDeviceSignatures(req *http.Request, keyserverAPI api.KeyInternalAPI, device *userapi.Device) util.JSONResponse {
+	uploadReq := &api.PerformUploadDeviceSignaturesRequest{}
+	uploadRes := &api.PerformUploadDeviceSignaturesResponse{}
+
+	if err := httputil.UnmarshalJSONRequest(req, &uploadReq.Signatures); err != nil {
+		return *err
+	}
+
+	uploadReq.UserID = device.UserID
+	keyserverAPI.PerformUploadDeviceSignatures(req.Context(), uploadReq, uploadRes)
+
+	if err := uploadRes.Error; err != nil {
+		switch {
+		case err.IsInvalidSignature:
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.InvalidSignature(err.Error()),
+			}
+		case err.IsMissingParam:
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.MissingParam(err.Error()),
+			}
+		default:
+			return util.JSONResponse{
+				Code: http.StatusBadRequest,
+				JSON: jsonerror.Unknown(err.Error()),
+			}
+		}
+	}
+
+	return util.JSONResponse{
+		Code: http.StatusOK,
+		JSON: struct{}{},
+	}
+}

clientapi/routing/keys.go

@@ -100,7 +100,7 @@ func (r *queryKeysRequest) GetTimeout() time.Duration {
 	return time.Duration(r.Timeout) * time.Millisecond
 }
 
-func QueryKeys(req *http.Request, keyAPI api.KeyInternalAPI) util.JSONResponse {
+func QueryKeys(req *http.Request, keyAPI api.KeyInternalAPI, device *userapi.Device) util.JSONResponse {
 	var r queryKeysRequest
 	resErr := httputil.UnmarshalJSONRequest(req, &r)
 	if resErr != nil {
@@ -108,6 +108,7 @@ func QueryKeys(req *http.Request, keyAPI api.KeyInternalAPI) util.JSONResponse {
 	}
 	queryRes := api.QueryKeysResponse{}
 	keyAPI.QueryKeys(req.Context(), &api.QueryKeysRequest{
+		UserID:        device.UserID,
 		UserToDevices: r.DeviceKeys,
 		Timeout:       r.GetTimeout(),
 		// TODO: Token?
@@ -115,8 +116,11 @@ func QueryKeys(req *http.Request, keyAPI api.KeyInternalAPI) util.JSONResponse {
 	return util.JSONResponse{
 		Code: 200,
 		JSON: map[string]interface{}{
-			"device_keys": queryRes.DeviceKeys,
-			"failures":    queryRes.Failures,
+			"device_keys":       queryRes.DeviceKeys,
+			"master_keys":       queryRes.MasterKeys,
+			"self_signing_keys": queryRes.SelfSigningKeys,
+			"user_signing_keys": queryRes.UserSigningKeys,
+			"failures":          queryRes.Failures,
 		},
 	}
 }

clientapi/routing/routing.go

@@ -64,7 +64,9 @@ func Setup(
 	rateLimits := newRateLimits(&cfg.RateLimiting)
 	userInteractiveAuth := auth.NewUserInteractive(accountDB.GetAccountByPassword, cfg)
 
-	unstableFeatures := make(map[string]bool)
+	unstableFeatures := map[string]bool{
+		//"org.matrix.e2e_cross_signing": true,
+	}
 	for _, msc := range cfg.MSCs.MSCs {
 		unstableFeatures["org.matrix."+msc] = true
 	}
@@ -1066,6 +1068,22 @@ func Setup(
 
 	// Deleting E2E Backup Keys
 
+	// Cross-signing device keys
+
+	postDeviceSigningKeys := httputil.MakeAuthAPI("post_device_signing_keys", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+		return UploadCrossSigningDeviceKeys(req, userInteractiveAuth, keyAPI, device, accountDB, cfg)
+	})
+
+	postDeviceSigningSignatures := httputil.MakeAuthAPI("post_device_signing_signatures", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+		return UploadCrossSigningDeviceSignatures(req, keyAPI, device)
+	})
+
+	r0mux.Handle("/keys/device_signing/upload", postDeviceSigningKeys).Methods(http.MethodPost, http.MethodOptions)
+	r0mux.Handle("/keys/signatures/upload", postDeviceSigningSignatures).Methods(http.MethodPost, http.MethodOptions)
+
+	unstableMux.Handle("/keys/device_signing/upload", postDeviceSigningKeys).Methods(http.MethodPost, http.MethodOptions)
+	unstableMux.Handle("/keys/signatures/upload", postDeviceSigningSignatures).Methods(http.MethodPost, http.MethodOptions)
+
 	// Supplying a device ID is deprecated.
 	r0mux.Handle("/keys/upload/{deviceID}",
 		httputil.MakeAuthAPI("keys_upload", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
@@ -1079,7 +1097,7 @@ func Setup(
 	).Methods(http.MethodPost, http.MethodOptions)
 	r0mux.Handle("/keys/query",
 		httputil.MakeAuthAPI("keys_query", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
-			return QueryKeys(req, keyAPI)
+			return QueryKeys(req, keyAPI, device)
 		}),
 	).Methods(http.MethodPost, http.MethodOptions)
 	r0mux.Handle("/keys/claim",

cmd/dendrite-demo-libp2p/main.go

@@ -147,7 +147,7 @@ func main() {
 
 	accountDB := base.Base.CreateAccountsDB()
 	federation := createFederationClient(base)
-	keyAPI := keyserver.NewInternalAPI(&base.Base.Cfg.KeyServer, federation)
+	keyAPI := keyserver.NewInternalAPI(&base.Base, &base.Base.Cfg.KeyServer, federation)
 	userAPI := userapi.NewInternalAPI(accountDB, &cfg.UserAPI, nil, keyAPI)
 	keyAPI.SetUserAPI(userAPI)
 

cmd/dendrite-demo-pinecone/main.go

@@ -179,7 +179,7 @@ func main() {
 		base, federation, rsAPI, keyRing, true,
 	)
 
-	keyAPI := keyserver.NewInternalAPI(&base.Cfg.KeyServer, fsAPI)
+	keyAPI := keyserver.NewInternalAPI(base, &base.Cfg.KeyServer, fsAPI)
 	userAPI := userapi.NewInternalAPI(accountDB, &cfg.UserAPI, nil, keyAPI)
 	keyAPI.SetUserAPI(userAPI)
 

cmd/dendrite-demo-yggdrasil/main.go

@@ -102,7 +102,7 @@ func main() {
 	serverKeyAPI := &signing.YggdrasilKeys{}
 	keyRing := serverKeyAPI.KeyRing()
 
-	keyAPI := keyserver.NewInternalAPI(&base.Cfg.KeyServer, federation)
+	keyAPI := keyserver.NewInternalAPI(base, &base.Cfg.KeyServer, federation)
 	userAPI := userapi.NewInternalAPI(accountDB, &cfg.UserAPI, nil, keyAPI)
 	keyAPI.SetUserAPI(userAPI)
 

cmd/dendrite-monolith-server/main.go

@@ -112,7 +112,7 @@ func main() {
 	// This is different to rsAPI which can be the http client which doesn't need this dependency
 	rsImpl.SetFederationSenderAPI(fsAPI)
 
-	keyAPI := keyserver.NewInternalAPI(&base.Cfg.KeyServer, fsAPI)
+	keyAPI := keyserver.NewInternalAPI(base, &base.Cfg.KeyServer, fsAPI)
 	userAPI := userapi.NewInternalAPI(accountDB, &cfg.UserAPI, cfg.Derived.ApplicationServices, keyAPI)
 	keyAPI.SetUserAPI(userAPI)
 	if traceInternal {

cmd/dendrite-polylith-multi/personalities/keyserver.go

@@ -22,7 +22,7 @@ import (
 
 func KeyServer(base *setup.BaseDendrite, cfg *config.Dendrite) {
 	fsAPI := base.FederationSenderHTTPClient()
-	intAPI := keyserver.NewInternalAPI(&base.Cfg.KeyServer, fsAPI)
+	intAPI := keyserver.NewInternalAPI(base, &base.Cfg.KeyServer, fsAPI)
 	intAPI.SetUserAPI(base.UserAPIClient())
 
 	keyserver.AddInternalRoutes(base.InternalAPIMux, intAPI)

cmd/dendritejs-pinecone/main.go

@@ -184,7 +184,7 @@ func startup() {
 
 	accountDB := base.CreateAccountsDB()
 	federation := conn.CreateFederationClient(base, pSessions)
-	keyAPI := keyserver.NewInternalAPI(&base.Cfg.KeyServer, federation)
+	keyAPI := keyserver.NewInternalAPI(base, &base.Cfg.KeyServer, federation)
 	userAPI := userapi.NewInternalAPI(accountDB, &cfg.UserAPI, nil, keyAPI)
 	keyAPI.SetUserAPI(userAPI)
 

cmd/dendritejs/main.go

@@ -192,7 +192,7 @@ func main() {
 
 	accountDB := base.CreateAccountsDB()
 	federation := createFederationClient(cfg, node)
-	keyAPI := keyserver.NewInternalAPI(&base.Cfg.KeyServer, federation)
+	keyAPI := keyserver.NewInternalAPI(base, &base.Cfg.KeyServer, federation)
 	userAPI := userapi.NewInternalAPI(accountDB, &cfg.UserAPI, nil, keyAPI)
 	keyAPI.SetUserAPI(userAPI)
 

keyserver/api/api.go

@@ -32,6 +32,8 @@ type KeyInternalAPI interface {
 	PerformUploadKeys(ctx context.Context, req *PerformUploadKeysRequest, res *PerformUploadKeysResponse)
 	// PerformClaimKeys claims one-time keys for use in pre-key messages
 	PerformClaimKeys(ctx context.Context, req *PerformClaimKeysRequest, res *PerformClaimKeysResponse)
+	PerformUploadDeviceKeys(ctx context.Context, req *PerformUploadDeviceKeysRequest, res *PerformUploadDeviceKeysResponse)
+	PerformUploadDeviceSignatures(ctx context.Context, req *PerformUploadDeviceSignaturesRequest, res *PerformUploadDeviceSignaturesResponse)
 	QueryKeys(ctx context.Context, req *QueryKeysRequest, res *QueryKeysResponse)
 	QueryKeyChanges(ctx context.Context, req *QueryKeyChangesRequest, res *QueryKeyChangesResponse)
 	QueryOneTimeKeys(ctx context.Context, req *QueryOneTimeKeysRequest, res *QueryOneTimeKeysResponse)
@@ -40,7 +42,9 @@ type KeyInternalAPI interface {
 
 // KeyError is returned if there was a problem performing/querying the server
 type KeyError struct {
-	Err string
+	Err                string `json:"error"`
+	IsInvalidSignature bool   `json:"is_invalid_signature,omitempty"` // M_INVALID_SIGNATURE
+	IsMissingParam     bool   `json:"is_missing_param,omitempty"`     // M_MISSING_PARAM
 }
 
 func (k *KeyError) Error() string {
@@ -151,7 +155,30 @@ type PerformClaimKeysResponse struct {
 	Error *KeyError
 }
 
+type PerformUploadDeviceKeysRequest struct {
+	gomatrixserverlib.CrossSigningKeys
+	// The user that uploaded the key, should be populated by the clientapi.
+	UserID string `json:"user_id"`
+}
+
+type PerformUploadDeviceKeysResponse struct {
+	Error *KeyError
+}
+
+type PerformUploadDeviceSignaturesRequest struct {
+	Signatures map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice
+	// The user that uploaded the sig, should be populated by the clientapi.
+	UserID string `json:"user_id"`
+}
+
+type PerformUploadDeviceSignaturesResponse struct {
+	Error *KeyError
+}
+
 type QueryKeysRequest struct {
+	// The user ID asking for the keys, e.g. if from a client API request.
+	// Will not be populated if the key request came from federation.
+	UserID string
 	// Maps user IDs to a list of devices
 	UserToDevices map[string][]string
 	Timeout       time.Duration
@@ -162,6 +189,10 @@ type QueryKeysResponse struct {
 	Failures map[string]interface{}
 	// Map of user_id to device_id to device_key
 	DeviceKeys map[string]map[string]json.RawMessage
+	// Maps of user_id to cross signing key
+	MasterKeys      map[string]gomatrixserverlib.CrossSigningKey
+	SelfSigningKeys map[string]gomatrixserverlib.CrossSigningKey
+	UserSigningKeys map[string]gomatrixserverlib.CrossSigningKey
 	// Set if there was a fatal error processing this query
 	Error *KeyError
 }

keyserver/consumers/eduserver.go

@@ -0,0 +1,61 @@
+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

@@ -0,0 +1,389 @@
+// 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 internal
+
+import (
+	"context"
+	"crypto/ed25519"
+	"encoding/json"
+	"fmt"
+	"strings"
+
+	"github.com/matrix-org/dendrite/keyserver/api"
+	"github.com/matrix-org/dendrite/keyserver/types"
+	"github.com/matrix-org/gomatrixserverlib"
+	"github.com/sirupsen/logrus"
+)
+
+func sanityCheckKey(key gomatrixserverlib.CrossSigningKey, userID string, purpose gomatrixserverlib.CrossSigningKeyPurpose) error {
+	// Is there exactly one key?
+	if len(key.Keys) != 1 {
+		return fmt.Errorf("should contain exactly one key")
+	}
+
+	// Does the key ID match the key value? Iterates exactly once
+	for keyID, keyData := range key.Keys {
+		b64 := keyData.Encode()
+		tokens := strings.Split(string(keyID), ":")
+		if len(tokens) != 2 {
+			return fmt.Errorf("key ID is incorrectly formatted")
+		}
+		if tokens[1] != b64 {
+			return fmt.Errorf("key ID isn't correct")
+		}
+	}
+
+	// Does the key claim to be from the right user?
+	if userID != key.UserID {
+		return fmt.Errorf("key has a user ID mismatch")
+	}
+
+	// Does the key contain the correct purpose?
+	useful := false
+	for _, usage := range key.Usage {
+		if usage == purpose {
+			useful = true
+			break
+		}
+	}
+	if !useful {
+		return fmt.Errorf("key does not contain correct usage purpose")
+	}
+
+	return nil
+}
+
+// nolint:gocyclo
+func (a *KeyInternalAPI) PerformUploadDeviceKeys(ctx context.Context, req *api.PerformUploadDeviceKeysRequest, res *api.PerformUploadDeviceKeysResponse) {
+	var masterKey gomatrixserverlib.Base64Bytes
+	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(),
+			}
+			return
+		}
+		hasMasterKey = true
+		for _, keyData := range req.MasterKey.Keys { // iterates once, because sanityCheckKey requires one key
+			masterKey = keyData
+		}
+	}
+
+	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(),
+			}
+			return
+		}
+	}
+
+	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(),
+			}
+			return
+		}
+	}
+
+	// If the user hasn't given a new master key, then let's go and get their
+	// existing keys from the database.
+	if !hasMasterKey {
+		existingKeys, err := a.DB.CrossSigningKeysForUser(ctx, req.UserID)
+		if err != nil {
+			res.Error = &api.KeyError{
+				Err: "Retrieving cross-signing keys from database failed: " + err.Error(),
+			}
+			return
+		}
+
+		masterKey, hasMasterKey = existingKeys[gomatrixserverlib.CrossSigningKeyPurposeMaster]
+	}
+
+	// If the user isn't a local user and we haven't successfully found a key
+	// through any local means then ask over federation.
+	if !hasMasterKey {
+		_, host, err := gomatrixserverlib.SplitID('@', req.UserID)
+		if err != nil {
+			res.Error = &api.KeyError{
+				Err: "Retrieving cross-signing keys from federation failed: " + err.Error(),
+			}
+			return
+		}
+		keys, err := a.FedClient.QueryKeys(ctx, host, map[string][]string{
+			req.UserID: {},
+		})
+		if err != nil {
+			res.Error = &api.KeyError{
+				Err: "Retrieving cross-signing keys from federation failed: " + err.Error(),
+			}
+			return
+		}
+		switch k := keys.MasterKeys[req.UserID].CrossSigningBody.(type) {
+		case *gomatrixserverlib.CrossSigningKey:
+			if err := sanityCheckKey(*k, req.UserID, gomatrixserverlib.CrossSigningKeyPurposeMaster); err != nil {
+				res.Error = &api.KeyError{
+					Err: "Master key sanity check failed: " + err.Error(),
+				}
+				return
+			}
+		default:
+			res.Error = &api.KeyError{
+				Err: "Unexpected type for master key retrieved from federation",
+			}
+			return
+		}
+	}
+
+	// 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 !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
+	}
+	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. We don't do this for
+		// the master key because we have no means to verify the signatures - we
+		// instead just need to store them.
+		if purpose != gomatrixserverlib.CrossSigningKeyPurposeMaster {
+			// Marshal the specific key back into JSON so that we can verify the
+			// signature of it.
+			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
+			}
+
+			// Now check if the subkey is 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 err := a.DB.StoreCrossSigningKeysForUser(ctx, req.UserID, toStore); err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("a.DB.StoreCrossSigningKeysForUser: %s", err),
+		}
+	}
+}
+
+func (a *KeyInternalAPI) PerformUploadDeviceSignatures(ctx context.Context, req *api.PerformUploadDeviceSignaturesRequest, res *api.PerformUploadDeviceSignaturesResponse) {
+	selfSignatures := map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+	otherSignatures := map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+
+	for userID, forUserID := range req.Signatures {
+		for keyID, keyOrDevice := range forUserID {
+			switch key := keyOrDevice.CrossSigningBody.(type) {
+			case *gomatrixserverlib.CrossSigningKey:
+				if key.UserID == req.UserID {
+					if _, ok := selfSignatures[userID]; !ok {
+						selfSignatures[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+					}
+					selfSignatures[userID][keyID] = keyOrDevice
+				} else {
+					if _, ok := otherSignatures[userID]; !ok {
+						otherSignatures[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+					}
+					otherSignatures[userID][keyID] = keyOrDevice
+				}
+
+			case *gomatrixserverlib.DeviceKeys:
+				if key.UserID == req.UserID {
+					if _, ok := selfSignatures[userID]; !ok {
+						selfSignatures[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+					}
+					selfSignatures[userID][keyID] = keyOrDevice
+				} else {
+					if _, ok := otherSignatures[userID]; !ok {
+						otherSignatures[userID] = map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice{}
+					}
+					otherSignatures[userID][keyID] = keyOrDevice
+				}
+
+			default:
+				continue
+			}
+		}
+	}
+
+	if err := a.processSelfSignatures(ctx, req.UserID, selfSignatures); err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("a.processSelfSignatures: %s", err),
+		}
+		return
+	}
+
+	if err := a.processOtherSignatures(ctx, req.UserID, otherSignatures); err != nil {
+		res.Error = &api.KeyError{
+			Err: fmt.Sprintf("a.processOtherSignatures: %s", err),
+		}
+		return
+	}
+}
+
+func (a *KeyInternalAPI) processSelfSignatures(
+	ctx context.Context, _ string,
+	signatures map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice,
+) error {
+	// Here we will process:
+	// * The user signing their own devices using their self-signing key
+	// * The user signing their master key using one of their devices
+
+	for targetUserID, forTargetUserID := range signatures {
+		for targetKeyID, signature := range forTargetUserID {
+			switch sig := signature.CrossSigningBody.(type) {
+			case *gomatrixserverlib.CrossSigningKey:
+				for originUserID, forOriginUserID := range sig.Signatures {
+					for originKeyID, originSig := range forOriginUserID {
+						if err := a.DB.StoreCrossSigningSigsForTarget(
+							ctx, originUserID, originKeyID, targetUserID, targetKeyID, originSig,
+						); err != nil {
+							return fmt.Errorf("a.DB.StoreCrossSigningKeysForTarget: %w", err)
+						}
+					}
+				}
+
+			case *gomatrixserverlib.DeviceKeys:
+				for originUserID, forOriginUserID := range sig.Signatures {
+					for originKeyID, originSig := range forOriginUserID {
+						if err := a.DB.StoreCrossSigningSigsForTarget(
+							ctx, originUserID, originKeyID, targetUserID, targetKeyID, originSig,
+						); err != nil {
+							return fmt.Errorf("a.DB.StoreCrossSigningKeysForTarget: %w", err)
+						}
+					}
+				}
+
+			default:
+				return fmt.Errorf("unexpected type assertion")
+			}
+		}
+	}
+
+	return nil
+}
+
+func (a *KeyInternalAPI) processOtherSignatures(
+	ctx context.Context, userID string,
+	signatures map[string]map[gomatrixserverlib.KeyID]gomatrixserverlib.CrossSigningForKeyOrDevice,
+) error {
+	// Here we will process:
+	// * A user signing someone else's master keys using their user-signing keys
+
+	return nil
+}
+
+func (a *KeyInternalAPI) crossSigningKeysFromDatabase(
+	ctx context.Context, req *api.QueryKeysRequest, res *api.QueryKeysResponse,
+) {
+	for userID := range req.UserToDevices {
+		keys, err := a.DB.CrossSigningKeysForUser(ctx, userID)
+		if err != nil {
+			logrus.WithError(err).Errorf("Failed to get cross-signing keys for user %q", userID)
+			continue
+		}
+
+		for keyType, keyData := range keys {
+			b64 := keyData.Encode()
+			keyID := gomatrixserverlib.KeyID("ed25519:" + b64)
+			key := gomatrixserverlib.CrossSigningKey{
+				UserID: userID,
+				Usage: []gomatrixserverlib.CrossSigningKeyPurpose{
+					keyType,
+				},
+				Keys: map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes{
+					keyID: keyData,
+				},
+			}
+
+			sigs, err := a.DB.CrossSigningSigsForTarget(ctx, userID, keyID)
+			if err != nil {
+				logrus.WithError(err).Errorf("Failed to get cross-signing signatures for user %q key %q", userID, keyID)
+				continue
+			}
+
+			appendSignature := func(originUserID string, originKeyID gomatrixserverlib.KeyID, signature gomatrixserverlib.Base64Bytes) {
+				if key.Signatures == nil {
+					key.Signatures = types.CrossSigningSigMap{}
+				}
+				if _, ok := key.Signatures[originUserID]; !ok {
+					key.Signatures[originUserID] = make(map[gomatrixserverlib.KeyID]gomatrixserverlib.Base64Bytes)
+				}
+				key.Signatures[originUserID][originKeyID] = signature
+			}
+
+			for originUserID, forOrigin := range sigs {
+				for originKeyID, signature := range forOrigin {
+					switch {
+					case req.UserID != "" && originUserID == req.UserID:
+						// Include signatures that we created
+						appendSignature(originUserID, originKeyID, signature)
+					case originUserID == userID:
+						// Include signatures that were created by the person whose key
+						// we are processing
+						appendSignature(originUserID, originKeyID, signature)
+					}
+				}
+			}
+
+			switch keyType {
+			case gomatrixserverlib.CrossSigningKeyPurposeMaster:
+				res.MasterKeys[userID] = key
+
+			case gomatrixserverlib.CrossSigningKeyPurposeSelfSigning:
+				res.SelfSigningKeys[userID] = key
+
+			case gomatrixserverlib.CrossSigningKeyPurposeUserSigning:
+				res.UserSigningKeys[userID] = key
+			}
+		}
+	}
+}

keyserver/internal/device_list_update.go

@@ -82,6 +82,7 @@ type DeviceListUpdater struct {
 	mu            *sync.Mutex // protects UserIDToMutex
 
 	db          DeviceListUpdaterDatabase
+	api         DeviceListUpdaterAPI
 	producer    KeyChangeProducer
 	fedClient   fedsenderapi.FederationClient
 	workerChans []chan gomatrixserverlib.ServerName
@@ -114,6 +115,10 @@ type DeviceListUpdaterDatabase interface {
 	DeviceKeysJSON(ctx context.Context, keys []api.DeviceMessage) error
 }
 
+type DeviceListUpdaterAPI interface {
+	PerformUploadDeviceKeys(ctx context.Context, req *api.PerformUploadDeviceKeysRequest, res *api.PerformUploadDeviceKeysResponse)
+}
+
 // KeyChangeProducer is the interface for producers.KeyChange useful for testing.
 type KeyChangeProducer interface {
 	ProduceKeyChanges(keys []api.DeviceMessage) error
@@ -121,13 +126,14 @@ type KeyChangeProducer interface {
 
 // NewDeviceListUpdater creates a new updater which fetches fresh device lists when they go stale.
 func NewDeviceListUpdater(
-	db DeviceListUpdaterDatabase, producer KeyChangeProducer, fedClient fedsenderapi.FederationClient,
-	numWorkers int,
+	db DeviceListUpdaterDatabase, api DeviceListUpdaterAPI, producer KeyChangeProducer,
+	fedClient fedsenderapi.FederationClient, numWorkers int,
 ) *DeviceListUpdater {
 	return &DeviceListUpdater{
 		userIDToMutex:  make(map[string]*sync.Mutex),
 		mu:             &sync.Mutex{},
 		db:             db,
+		api:            api,
 		producer:       producer,
 		fedClient:      fedClient,
 		workerChans:    make([]chan gomatrixserverlib.ServerName, numWorkers),
@@ -367,6 +373,23 @@ func (u *DeviceListUpdater) processServer(serverName gomatrixserverlib.ServerNam
 			}
 			continue
 		}
+		if res.MasterKey != nil || res.SelfSigningKey != nil {
+			uploadReq := &api.PerformUploadDeviceKeysRequest{
+				UserID: userID,
+			}
+			uploadRes := &api.PerformUploadDeviceKeysResponse{}
+			if res.MasterKey != nil {
+				if err = sanityCheckKey(*res.MasterKey, userID, gomatrixserverlib.CrossSigningKeyPurposeMaster); err == nil {
+					uploadReq.MasterKey = *res.MasterKey
+				}
+			}
+			if res.SelfSigningKey != nil {
+				if err = sanityCheckKey(*res.SelfSigningKey, userID, gomatrixserverlib.CrossSigningKeyPurposeSelfSigning); err == nil {
+					uploadReq.SelfSigningKey = *res.SelfSigningKey
+				}
+			}
+			u.api.PerformUploadDeviceKeys(ctx, uploadReq, uploadRes)
+		}
 		err = u.updateDeviceList(&res)
 		if err != nil {
 			logger.WithError(err).WithField("user_id", userID).Error("fetched device list but failed to store/emit it")

keyserver/internal/device_list_update_test.go

@@ -95,6 +95,13 @@ func (d *mockDeviceListUpdaterDatabase) DeviceKeysJSON(ctx context.Context, keys
 	return nil
 }
 
+type mockDeviceListUpdaterAPI struct {
+}
+
+func (d *mockDeviceListUpdaterAPI) PerformUploadDeviceKeys(ctx context.Context, req *api.PerformUploadDeviceKeysRequest, res *api.PerformUploadDeviceKeysResponse) {
+
+}
+
 type roundTripper struct {
 	fn func(*http.Request) (*http.Response, error)
 }
@@ -122,8 +129,9 @@ func TestUpdateHavePrevID(t *testing.T) {
 			return true
 		},
 	}
+	ap := &mockDeviceListUpdaterAPI{}
 	producer := &mockKeyChangeProducer{}
-	updater := NewDeviceListUpdater(db, producer, nil, 1)
+	updater := NewDeviceListUpdater(db, ap, producer, nil, 1)
 	event := gomatrixserverlib.DeviceListUpdateEvent{
 		DeviceDisplayName: "Foo Bar",
 		Deleted:           false,
@@ -166,6 +174,7 @@ func TestUpdateNoPrevID(t *testing.T) {
 			return false
 		},
 	}
+	ap := &mockDeviceListUpdaterAPI{}
 	producer := &mockKeyChangeProducer{}
 	remoteUserID := "@alice:example.somewhere"
 	var wg sync.WaitGroup
@@ -193,7 +202,7 @@ func TestUpdateNoPrevID(t *testing.T) {
 			`)),
 		}, nil
 	})
-	updater := NewDeviceListUpdater(db, producer, fedClient, 2)
+	updater := NewDeviceListUpdater(db, ap, producer, fedClient, 2)
 	if err := updater.Start(); err != nil {
 		t.Fatalf("failed to start updater: %s", err)
 	}

keyserver/internal/internal.go

@@ -221,9 +221,17 @@ func (a *KeyInternalAPI) QueryDeviceMessages(ctx context.Context, req *api.Query
 
 func (a *KeyInternalAPI) QueryKeys(ctx context.Context, req *api.QueryKeysRequest, res *api.QueryKeysResponse) {
 	res.DeviceKeys = make(map[string]map[string]json.RawMessage)
+	res.MasterKeys = make(map[string]gomatrixserverlib.CrossSigningKey)
+	res.SelfSigningKeys = make(map[string]gomatrixserverlib.CrossSigningKey)
+	res.UserSigningKeys = make(map[string]gomatrixserverlib.CrossSigningKey)
 	res.Failures = make(map[string]interface{})
+
+	// get cross-signing keys from the database
+	a.crossSigningKeysFromDatabase(ctx, req, res)
+
 	// make a map from domain to device keys
 	domainToDeviceKeys := make(map[string]map[string][]string)
+	domainToCrossSigningKeys := make(map[string]map[string]struct{})
 	for userID, deviceIDs := range req.UserToDevices {
 		_, serverName, err := gomatrixserverlib.SplitID('@', userID)
 		if err != nil {
@@ -274,16 +282,30 @@ func (a *KeyInternalAPI) QueryKeys(ctx context.Context, req *api.QueryKeysReques
 			domainToDeviceKeys[domain] = make(map[string][]string)
 			domainToDeviceKeys[domain][userID] = append(domainToDeviceKeys[domain][userID], deviceIDs...)
 		}
+		// work out if our cross-signing request for this user was
+		// satisfied, if not add them to the list of things to fetch
+		if _, ok := res.MasterKeys[userID]; !ok {
+			if _, ok := domainToCrossSigningKeys[domain]; !ok {
+				domainToCrossSigningKeys[domain] = make(map[string]struct{})
+			}
+			domainToCrossSigningKeys[domain][userID] = struct{}{}
+		}
+		if _, ok := res.SelfSigningKeys[userID]; !ok {
+			if _, ok := domainToCrossSigningKeys[domain]; !ok {
+				domainToCrossSigningKeys[domain] = make(map[string]struct{})
+			}
+			domainToCrossSigningKeys[domain][userID] = struct{}{}
+		}
 	}
 
 	// attempt to satisfy key queries from the local database first as we should get device updates pushed to us
 	domainToDeviceKeys = a.remoteKeysFromDatabase(ctx, res, domainToDeviceKeys)
-	if len(domainToDeviceKeys) == 0 {
+	if len(domainToDeviceKeys) == 0 && len(domainToCrossSigningKeys) == 0 {
 		return // nothing to query
 	}
 
 	// perform key queries for remote devices
-	a.queryRemoteKeys(ctx, req.Timeout, res, domainToDeviceKeys)
+	a.queryRemoteKeys(ctx, req.Timeout, res, domainToDeviceKeys, domainToCrossSigningKeys)
 }
 
 func (a *KeyInternalAPI) remoteKeysFromDatabase(
@@ -313,18 +335,30 @@ func (a *KeyInternalAPI) remoteKeysFromDatabase(
 }
 
 func (a *KeyInternalAPI) queryRemoteKeys(
-	ctx context.Context, timeout time.Duration, res *api.QueryKeysResponse, domainToDeviceKeys map[string]map[string][]string,
+	ctx context.Context, timeout time.Duration, res *api.QueryKeysResponse,
+	domainToDeviceKeys map[string]map[string][]string, domainToCrossSigningKeys map[string]map[string]struct{},
 ) {
 	resultCh := make(chan *gomatrixserverlib.RespQueryKeys, len(domainToDeviceKeys))
 	// allows us to wait until all federation servers have been poked
 	var wg sync.WaitGroup
-	wg.Add(len(domainToDeviceKeys))
 	// mutex for writing directly to res (e.g failures)
 	var respMu sync.Mutex
 
+	domains := map[string]struct{}{}
+	for domain := range domainToDeviceKeys {
+		domains[domain] = struct{}{}
+	}
+	for domain := range domainToCrossSigningKeys {
+		domains[domain] = struct{}{}
+	}
+	wg.Add(len(domains))
+
 	// fan out
-	for domain, deviceKeys := range domainToDeviceKeys {
-		go a.queryRemoteKeysOnServer(ctx, domain, deviceKeys, &wg, &respMu, timeout, resultCh, res)
+	for domain := range domains {
+		go a.queryRemoteKeysOnServer(
+			ctx, domain, domainToDeviceKeys[domain], domainToCrossSigningKeys[domain],
+			&wg, &respMu, timeout, resultCh, res,
+		)
 	}
 
 	// Close the result channel when the goroutines have quit so the for .. range exits
@@ -344,12 +378,29 @@ func (a *KeyInternalAPI) queryRemoteKeys(
 				res.DeviceKeys[userID][deviceID] = keyJSON
 			}
 		}
+
+		for userID, body := range result.MasterKeys {
+			switch b := body.CrossSigningBody.(type) {
+			case *gomatrixserverlib.CrossSigningKey:
+				res.MasterKeys[userID] = *b
+			}
+		}
+
+		for userID, body := range result.SelfSigningKeys {
+			switch b := body.CrossSigningBody.(type) {
+			case *gomatrixserverlib.CrossSigningKey:
+				res.SelfSigningKeys[userID] = *b
+			}
+		}
+
+		// TODO: do we want to persist these somewhere now
+		// that we have fetched them?
 	}
 }
 
 func (a *KeyInternalAPI) queryRemoteKeysOnServer(
-	ctx context.Context, serverName string, devKeys map[string][]string, wg *sync.WaitGroup,
-	respMu *sync.Mutex, timeout time.Duration, resultCh chan<- *gomatrixserverlib.RespQueryKeys,
+	ctx context.Context, serverName string, devKeys map[string][]string, crossSigningKeys map[string]struct{},
+	wg *sync.WaitGroup, respMu *sync.Mutex, timeout time.Duration, resultCh chan<- *gomatrixserverlib.RespQueryKeys,
 	res *api.QueryKeysResponse,
 ) {
 	defer wg.Done()
@@ -358,14 +409,24 @@ func (a *KeyInternalAPI) queryRemoteKeysOnServer(
 	// for users who we do not have any knowledge about, try to start doing device list updates for them
 	// by hitting /users/devices - otherwise fallback to /keys/query which has nicer bulk properties but
 	// lack a stream ID.
-	var userIDsForAllDevices []string
+	userIDsForAllDevices := map[string]struct{}{}
 	for userID, deviceIDs := range devKeys {
 		if len(deviceIDs) == 0 {
-			userIDsForAllDevices = append(userIDsForAllDevices, userID)
+			userIDsForAllDevices[userID] = struct{}{}
 			delete(devKeys, userID)
 		}
 	}
-	for _, userID := range userIDsForAllDevices {
+	// for cross-signing keys, it's probably easier just to hit /keys/query if we aren't already doing
+	// a device list update, so we'll populate those back into the /keys/query list if not
+	for userID := range crossSigningKeys {
+		if devKeys == nil {
+			devKeys = map[string][]string{}
+		}
+		if _, ok := userIDsForAllDevices[userID]; !ok {
+			devKeys[userID] = []string{}
+		}
+	}
+	for userID := range userIDsForAllDevices {
 		err := a.Updater.ManualUpdate(context.Background(), gomatrixserverlib.ServerName(serverName), userID)
 		if err != nil {
 			logrus.WithFields(logrus.Fields{

keyserver/inthttp/client.go

@@ -27,13 +27,15 @@ import (
 
 // HTTP paths for the internal HTTP APIs
 const (
-	InputDeviceListUpdatePath = "/keyserver/inputDeviceListUpdate"
-	PerformUploadKeysPath     = "/keyserver/performUploadKeys"
-	PerformClaimKeysPath      = "/keyserver/performClaimKeys"
-	QueryKeysPath             = "/keyserver/queryKeys"
-	QueryKeyChangesPath       = "/keyserver/queryKeyChanges"
-	QueryOneTimeKeysPath      = "/keyserver/queryOneTimeKeys"
-	QueryDeviceMessagesPath   = "/keyserver/queryDeviceMessages"
+	InputDeviceListUpdatePath         = "/keyserver/inputDeviceListUpdate"
+	PerformUploadKeysPath             = "/keyserver/performUploadKeys"
+	PerformClaimKeysPath              = "/keyserver/performClaimKeys"
+	PerformUploadDeviceKeysPath       = "/keyserver/performUploadDeviceKeys"
+	PerformUploadDeviceSignaturesPath = "/keyserver/performUploadDeviceSignatures"
+	QueryKeysPath                     = "/keyserver/queryKeys"
+	QueryKeyChangesPath               = "/keyserver/queryKeyChanges"
+	QueryOneTimeKeysPath              = "/keyserver/queryOneTimeKeys"
+	QueryDeviceMessagesPath           = "/keyserver/queryDeviceMessages"
 )
 
 // NewKeyServerClient creates a KeyInternalAPI implemented by talking to a HTTP POST API.
@@ -175,3 +177,37 @@ func (h *httpKeyInternalAPI) QueryKeyChanges(
 		}
 	}
 }
+
+func (h *httpKeyInternalAPI) PerformUploadDeviceKeys(
+	ctx context.Context,
+	request *api.PerformUploadDeviceKeysRequest,
+	response *api.PerformUploadDeviceKeysResponse,
+) {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "PerformUploadDeviceKeys")
+	defer span.Finish()
+
+	apiURL := h.apiURL + PerformUploadDeviceKeysPath
+	err := httputil.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+	if err != nil {
+		response.Error = &api.KeyError{
+			Err: err.Error(),
+		}
+	}
+}
+
+func (h *httpKeyInternalAPI) PerformUploadDeviceSignatures(
+	ctx context.Context,
+	request *api.PerformUploadDeviceSignaturesRequest,
+	response *api.PerformUploadDeviceSignaturesResponse,
+) {
+	span, ctx := opentracing.StartSpanFromContext(ctx, "PerformUploadDeviceSignatures")
+	defer span.Finish()
+
+	apiURL := h.apiURL + PerformUploadDeviceSignaturesPath
+	err := httputil.PostJSON(ctx, span, h.httpClient, apiURL, request, response)
+	if err != nil {
+		response.Error = &api.KeyError{
+			Err: err.Error(),
+		}
+	}
+}

keyserver/inthttp/server.go

@@ -58,6 +58,28 @@ func AddRoutes(internalAPIMux *mux.Router, s api.KeyInternalAPI) {
 			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
 		}),
 	)
+	internalAPIMux.Handle(PerformUploadDeviceKeysPath,
+		httputil.MakeInternalAPI("performUploadDeviceKeys", func(req *http.Request) util.JSONResponse {
+			request := api.PerformUploadDeviceKeysRequest{}
+			response := api.PerformUploadDeviceKeysResponse{}
+			if err := json.NewDecoder(req.Body).Decode(&request.CrossSigningKeys); err != nil {
+				return util.MessageResponse(http.StatusBadRequest, err.Error())
+			}
+			s.PerformUploadDeviceKeys(req.Context(), &request, &response)
+			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
+		}),
+	)
+	internalAPIMux.Handle(PerformUploadDeviceSignaturesPath,
+		httputil.MakeInternalAPI("performUploadDeviceSignatures", func(req *http.Request) util.JSONResponse {
+			request := api.PerformUploadDeviceSignaturesRequest{}
+			response := api.PerformUploadDeviceSignaturesResponse{}
+			if err := json.NewDecoder(req.Body).Decode(&request.Signatures); err != nil {
+				return util.MessageResponse(http.StatusBadRequest, err.Error())
+			}
+			s.PerformUploadDeviceSignatures(req.Context(), &request, &response)
+			return util.JSONResponse{Code: http.StatusOK, JSON: &response}
+		}),
+	)
 	internalAPIMux.Handle(QueryKeysPath,
 		httputil.MakeInternalAPI("queryKeys", func(req *http.Request) util.JSONResponse {
 			request := api.QueryKeysRequest{}

keyserver/keyserver.go

@@ -18,10 +18,12 @@ import (
 	"github.com/gorilla/mux"
 	fedsenderapi "github.com/matrix-org/dendrite/federationsender/api"
 	"github.com/matrix-org/dendrite/keyserver/api"
+	"github.com/matrix-org/dendrite/keyserver/consumers"
 	"github.com/matrix-org/dendrite/keyserver/internal"
 	"github.com/matrix-org/dendrite/keyserver/inthttp"
 	"github.com/matrix-org/dendrite/keyserver/producers"
 	"github.com/matrix-org/dendrite/keyserver/storage"
+	"github.com/matrix-org/dendrite/setup"
 	"github.com/matrix-org/dendrite/setup/config"
 	"github.com/matrix-org/dendrite/setup/kafka"
 	"github.com/sirupsen/logrus"
@@ -36,9 +38,9 @@ func AddInternalRoutes(router *mux.Router, intAPI api.KeyInternalAPI) {
 // NewInternalAPI returns a concerete implementation of the internal API. Callers
 // can call functions directly on the returned API or via an HTTP interface using AddInternalRoutes.
 func NewInternalAPI(
-	cfg *config.KeyServer, fedClient fedsenderapi.FederationClient,
+	base *setup.BaseDendrite, cfg *config.KeyServer, fedClient fedsenderapi.FederationClient,
 ) api.KeyInternalAPI {
-	_, producer := kafka.SetupConsumerProducer(&cfg.Matrix.Kafka)
+	consumer, producer := kafka.SetupConsumerProducer(&cfg.Matrix.Kafka)
 
 	db, err := storage.NewDatabase(&cfg.Database)
 	if err != nil {
@@ -49,17 +51,26 @@ func NewInternalAPI(
 		Producer: producer,
 		DB:       db,
 	}
-	updater := internal.NewDeviceListUpdater(db, keyChangeProducer, fedClient, 8) // 8 workers TODO: configurable
+	ap := &internal.KeyInternalAPI{
+		DB:         db,
+		ThisServer: cfg.Matrix.ServerName,
+		FedClient:  fedClient,
+		Producer:   keyChangeProducer,
+	}
+	updater := internal.NewDeviceListUpdater(db, ap, keyChangeProducer, fedClient, 8) // 8 workers TODO: configurable
+	ap.Updater = updater
 	go func() {
 		if err := updater.Start(); err != nil {
 			logrus.WithError(err).Panicf("failed to start device list updater")
 		}
 	}()
-	return &internal.KeyInternalAPI{
-		DB:         db,
-		ThisServer: cfg.Matrix.ServerName,
-		FedClient:  fedClient,
-		Producer:   keyChangeProducer,
-		Updater:    updater,
+
+	keyconsumer := consumers.NewOutputSigningKeyUpdateConsumer(
+		base.ProcessContext, base.Cfg, consumer, db, ap,
+	)
+	if err := keyconsumer.Start(); err != nil {
+		logrus.WithError(err).Panicf("failed to start keyserver EDU server consumer")
 	}
+
+	return ap
 }

setup/config/config_kafka.go

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

syncapi/internal/keychange_test.go

@@ -33,6 +33,10 @@ func (k *mockKeyAPI) SetUserAPI(i userapi.UserInternalAPI) {}
 // PerformClaimKeys claims one-time keys for use in pre-key messages
 func (k *mockKeyAPI) PerformClaimKeys(ctx context.Context, req *keyapi.PerformClaimKeysRequest, res *keyapi.PerformClaimKeysResponse) {
 }
+func (k *mockKeyAPI) PerformUploadDeviceKeys(ctx context.Context, req *keyapi.PerformUploadDeviceKeysRequest, res *keyapi.PerformUploadDeviceKeysResponse) {
+}
+func (k *mockKeyAPI) PerformUploadDeviceSignatures(ctx context.Context, req *keyapi.PerformUploadDeviceSignaturesRequest, res *keyapi.PerformUploadDeviceSignaturesResponse) {
+}
 func (k *mockKeyAPI) QueryKeys(ctx context.Context, req *keyapi.QueryKeysRequest, res *keyapi.QueryKeysResponse) {
 }
 func (k *mockKeyAPI) QueryKeyChanges(ctx context.Context, req *keyapi.QueryKeyChangesRequest, res *keyapi.QueryKeyChangesResponse) {

sytest-whitelist

@@ -550,3 +550,6 @@ Will not back up to an old backup version
 Can create more than 10 backup versions
 Can delete backup
 Deleted & recreated backups are empty
+Can upload self-signing keys
+Fails to upload self-signing keys with no auth
+Fails to upload self-signing key without master key