Key Backups (2/3) : Add E2E backup key tables (#1945)

* Add PUT key backup endpoints and glue them to PerformKeyBackup

* Add tables for storing backup keys and glue them into the user API

* Don't create tables whilst still WIPing

* writer on sqlite please

* Linting

clientapi/routing/key_backup.go

@@ -42,6 +42,17 @@ type keyBackupVersionResponse struct {
 	Version   string          `json:"version"`
 }
 
+type keyBackupSessionRequest struct {
+	Rooms map[string]struct {
+		Sessions map[string]userapi.KeyBackupSession `json:"sessions"`
+	} `json:"rooms"`
+}
+
+type keyBackupSessionResponse struct {
+	Count int64  `json:"count"`
+	ETag  string `json:"etag"`
+}
+
 // Create a new key backup. Request must contain a `keyBackupVersion`. Returns a `keyBackupVersionCreateResponse`.
 // Implements  POST /_matrix/client/r0/room_keys/version
 func CreateKeyBackupVersion(req *http.Request, userAPI userapi.UserInternalAPI, device *userapi.Device) util.JSONResponse {
@@ -171,3 +182,37 @@ func DeleteKeyBackupVersion(req *http.Request, userAPI userapi.UserInternalAPI,
 		},
 	}
 }
+
+// Upload a bunch of session keys for a given `version`.
+func UploadBackupKeys(
+	req *http.Request, userAPI userapi.UserInternalAPI, device *userapi.Device, version string, keys *keyBackupSessionRequest,
+) util.JSONResponse {
+	var performKeyBackupResp userapi.PerformKeyBackupResponse
+	userAPI.PerformKeyBackup(req.Context(), &userapi.PerformKeyBackupRequest{
+		UserID:  device.UserID,
+		Version: version,
+		Keys:    *keys,
+	}, &performKeyBackupResp)
+	if performKeyBackupResp.Error != "" {
+		if performKeyBackupResp.BadInput {
+			return util.JSONResponse{
+				Code: 400,
+				JSON: jsonerror.InvalidArgumentValue(performKeyBackupResp.Error),
+			}
+		}
+		return util.ErrorResponse(fmt.Errorf("PerformKeyBackup: %s", performKeyBackupResp.Error))
+	}
+	if !performKeyBackupResp.Exists {
+		return util.JSONResponse{
+			Code: 404,
+			JSON: jsonerror.NotFound("backup version not found"),
+		}
+	}
+	return util.JSONResponse{
+		Code: 200,
+		JSON: keyBackupSessionResponse{
+			Count: performKeyBackupResp.KeyCount,
+			ETag:  performKeyBackupResp.KeyETag,
+		},
+	}
+}

clientapi/routing/routing.go

@@ -938,6 +938,85 @@ func Setup(
 		}),
 	).Methods(http.MethodPost, http.MethodOptions)
 
+	// E2E Backup Keys
+	// Bulk room and session
+	r0mux.Handle("/room_keys/keys",
+		httputil.MakeAuthAPI("put_backup_keys", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			version := req.URL.Query().Get("version")
+			if version == "" {
+				return util.JSONResponse{
+					Code: 400,
+					JSON: jsonerror.InvalidArgumentValue("version must be specified"),
+				}
+			}
+			var reqBody keyBackupSessionRequest
+			resErr := clientutil.UnmarshalJSONRequest(req, &reqBody)
+			if resErr != nil {
+				return *resErr
+			}
+			return UploadBackupKeys(req, userAPI, device, version, &reqBody)
+		}),
+	).Methods(http.MethodPut)
+	// Single room bulk session
+	r0mux.Handle("/room_keys/keys/{roomID}",
+		httputil.MakeAuthAPI("put_backup_keys_room", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
+			if err != nil {
+				return util.ErrorResponse(err)
+			}
+			version := req.URL.Query().Get("version")
+			if version == "" {
+				return util.JSONResponse{
+					Code: 400,
+					JSON: jsonerror.InvalidArgumentValue("version must be specified"),
+				}
+			}
+			roomID := vars["roomID"]
+			var reqBody keyBackupSessionRequest
+			reqBody.Rooms[roomID] = struct {
+				Sessions map[string]userapi.KeyBackupSession `json:"sessions"`
+			}{
+				Sessions: map[string]userapi.KeyBackupSession{},
+			}
+			body := reqBody.Rooms[roomID]
+			resErr := clientutil.UnmarshalJSONRequest(req, &body)
+			if resErr != nil {
+				return *resErr
+			}
+			reqBody.Rooms[roomID] = body
+			return UploadBackupKeys(req, userAPI, device, version, &reqBody)
+		}),
+	).Methods(http.MethodPut)
+	// Single room, single session
+	r0mux.Handle("/room_keys/keys/{roomID}/{sessionID}",
+		httputil.MakeAuthAPI("put_backup_keys_room", userAPI, func(req *http.Request, device *userapi.Device) util.JSONResponse {
+			vars, err := httputil.URLDecodeMapValues(mux.Vars(req))
+			if err != nil {
+				return util.ErrorResponse(err)
+			}
+			version := req.URL.Query().Get("version")
+			if version == "" {
+				return util.JSONResponse{
+					Code: 400,
+					JSON: jsonerror.InvalidArgumentValue("version must be specified"),
+				}
+			}
+			var reqBody userapi.KeyBackupSession
+			resErr := clientutil.UnmarshalJSONRequest(req, &reqBody)
+			if resErr != nil {
+				return *resErr
+			}
+			roomID := vars["roomID"]
+			sessionID := vars["sessionID"]
+			var keyReq keyBackupSessionRequest
+			keyReq.Rooms[roomID] = struct {
+				Sessions map[string]userapi.KeyBackupSession `json:"sessions"`
+			}{}
+			keyReq.Rooms[roomID].Sessions[sessionID] = reqBody
+			return UploadBackupKeys(req, userAPI, device, version, &keyReq)
+		}),
+	).Methods(http.MethodPut)
+
 	// 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 {

sytest-whitelist

@@ -540,4 +540,3 @@ Key notary server must not overwrite a valid key with a spurious result from the
 GET /rooms/:room_id/aliases lists aliases
 Only room members can list aliases of a room
 Users with sufficient power-level can delete other's aliases
-Can create more than 10 backup versions

userapi/api/api.go

@@ -50,13 +50,39 @@ type PerformKeyBackupRequest struct {
 	AuthData     json.RawMessage
 	Algorithm    string
 	DeleteBackup bool // if true will delete the backup based on 'Version'.
+
+	// The keys to upload, if any. If blank, creates/updates/deletes key version metadata only.
+	Keys struct {
+		Rooms map[string]struct {
+			Sessions map[string]KeyBackupSession `json:"sessions"`
+		} `json:"rooms"`
+	}
+}
+
+// KeyBackupData in https://spec.matrix.org/unstable/client-server-api/#get_matrixclientr0room_keyskeysroomidsessionid
+type KeyBackupSession struct {
+	FirstMessageIndex int             `json:"first_message_index"`
+	ForwardedCount    int             `json:"forwarded_count"`
+	IsVerified        bool            `json:"is_verified"`
+	SessionData       json.RawMessage `json:"session_data"`
+}
+
+// Internal KeyBackupData for passing to/from the storage layer
+type InternalKeyBackupSession struct {
+	KeyBackupSession
+	RoomID    string
+	SessionID string
 }
 
 type PerformKeyBackupResponse struct {
 	Error    string // set if there was a problem performing the request
 	BadInput bool   // if set, the Error was due to bad input (HTTP 400)
+
 	Exists  bool   // set to true if the Version exists
-	Version  string
+	Version string // the newly created version
+
+	KeyCount int64  // only set if Keys were given in the request
+	KeyETag  string // only set if Keys were given in the request
 }
 
 type QueryKeyBackupRequest struct {

userapi/internal/api.go

@@ -444,7 +444,7 @@ func (a *UserInternalAPI) QueryOpenIDToken(ctx context.Context, req *api.QueryOp
 }
 
 func (a *UserInternalAPI) PerformKeyBackup(ctx context.Context, req *api.PerformKeyBackupRequest, res *api.PerformKeyBackupResponse) {
-	// Delete
+	// Delete metadata
 	if req.DeleteBackup {
 		if req.Version == "" {
 			res.BadInput = true
@@ -459,7 +459,7 @@ func (a *UserInternalAPI) PerformKeyBackup(ctx context.Context, req *api.Perform
 		res.Version = req.Version
 		return
 	}
-	// Create
+	// Create metadata
 	if req.Version == "" {
 		version, err := a.AccountDB.CreateKeyBackup(ctx, req.UserID, req.Algorithm, req.AuthData)
 		if err != nil {
@@ -469,16 +469,55 @@ func (a *UserInternalAPI) PerformKeyBackup(ctx context.Context, req *api.Perform
 		res.Version = version
 		return
 	}
-	// Update
+	// Update metadata
+	if len(req.Keys.Rooms) == 0 {
 		err := a.AccountDB.UpdateKeyBackupAuthData(ctx, req.UserID, req.Version, req.AuthData)
 		if err != nil {
 			res.Error = fmt.Sprintf("failed to update backup: %s", err)
 		}
 		res.Version = req.Version
+		return
+	}
+	// Upload Keys for a specific version metadata
+	a.uploadBackupKeys(ctx, req, res)
+}
+
+func (a *UserInternalAPI) uploadBackupKeys(ctx context.Context, req *api.PerformKeyBackupRequest, res *api.PerformKeyBackupResponse) {
+	// ensure the version metadata exists
+	version, _, _, _, deleted, err := a.AccountDB.GetKeyBackup(ctx, req.UserID, req.Version)
+	if err != nil {
+		res.Error = fmt.Sprintf("failed to query version: %s", err)
+		return
+	}
+	if deleted {
+		res.Error = "backup was deleted"
+		return
+	}
+	res.Exists = true
+	res.Version = version
+
+	// map keys to a form we can upload more easily - the map ensures we have no duplicates.
+	var uploads []api.InternalKeyBackupSession
+	for roomID, data := range req.Keys.Rooms {
+		for sessionID, sessionData := range data.Sessions {
+			uploads = append(uploads, api.InternalKeyBackupSession{
+				RoomID:           roomID,
+				SessionID:        sessionID,
+				KeyBackupSession: sessionData,
+			})
+		}
+	}
+	count, etag, err := a.AccountDB.UpsertBackupKeys(ctx, version, req.UserID, uploads)
+	if err != nil {
+		res.Error = fmt.Sprintf("failed to upsert keys: %s", err)
+		return
+	}
+	res.KeyCount = count
+	res.KeyETag = etag
 }
 
 func (a *UserInternalAPI) QueryKeyBackup(ctx context.Context, req *api.QueryKeyBackupRequest, res *api.QueryKeyBackupResponse) {
-	version, algorithm, authData, deleted, err := a.AccountDB.GetKeyBackup(ctx, req.UserID, req.Version)
+	version, algorithm, authData, etag, deleted, err := a.AccountDB.GetKeyBackup(ctx, req.UserID, req.Version)
 	res.Version = version
 	if err != nil {
 		if err == sql.ErrNoRows {
@@ -494,5 +533,5 @@ func (a *UserInternalAPI) QueryKeyBackup(ctx context.Context, req *api.QueryKeyB
 
 	// TODO:
 	res.Count = 0
-	res.ETag = ""
+	res.ETag = etag
 }

userapi/storage/accounts/interface.go

@@ -59,7 +59,8 @@ type Database interface {
 	CreateKeyBackup(ctx context.Context, userID, algorithm string, authData json.RawMessage) (version string, err error)
 	UpdateKeyBackupAuthData(ctx context.Context, userID, version string, authData json.RawMessage) (err error)
 	DeleteKeyBackup(ctx context.Context, userID, version string) (exists bool, err error)
-	GetKeyBackup(ctx context.Context, userID, version string) (versionResult, algorithm string, authData json.RawMessage, deleted bool, err error)
+	GetKeyBackup(ctx context.Context, userID, version string) (versionResult, algorithm string, authData json.RawMessage, etag string, deleted bool, err error)
+	UpsertBackupKeys(ctx context.Context, version, userID string, uploads []api.InternalKeyBackupSession) (count int64, etag string, err error)
 }
 
 // Err3PIDInUse is the error returned when trying to save an association involving

userapi/storage/accounts/postgres/key_backup_table.go

@@ -0,0 +1,134 @@
+// 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 postgres
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/userapi/api"
+)
+
+const keyBackupTableSchema = `
+CREATE TABLE IF NOT EXISTS account_e2e_room_keys (
+    user_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    session_id TEXT NOT NULL,
+
+    version TEXT NOT NULL,
+    first_message_index INTEGER NOT NULL,
+    forwarded_count INTEGER NOT NULL,
+    is_verified BOOLEAN NOT NULL,
+    session_data TEXT NOT NULL
+);
+CREATE UNIQUE INDEX IF NOT EXISTS e2e_room_keys_idx ON account_e2e_room_keys(user_id, room_id, session_id);
+`
+
+const insertBackupKeySQL = "" +
+	"INSERT INTO account_e2e_room_keys(user_id, room_id, session_id, version, first_message_index, forwarded_count, is_verified, session_data) " +
+	"VALUES ($1, $2, $3, $4, $5, $6, $7, $8)"
+
+const updateBackupKeySQL = "" +
+	"UPDATE account_e2e_room_keys SET first_message_index=$1, forwarded_count=$2, is_verified=$3, session_data=$4 " +
+	"WHERE user_id=$5 AND room_id=$6 AND session_id=$7 AND version=$8"
+
+const countKeysSQL = "" +
+	"SELECT COUNT(*) FROM account_e2e_room_keys WHERE user_id = $1 AND version = $2"
+
+const selectKeysSQL = "" +
+	"SELECT room_id, session_id, first_message_index, forwarded_count, is_verified, session_data FROM account_e2e_room_keys " +
+	"WHERE user_id = $1 AND version = $2"
+
+type keyBackupStatements struct {
+	insertBackupKeyStmt *sql.Stmt
+	updateBackupKeyStmt *sql.Stmt
+	countKeysStmt       *sql.Stmt
+	selectKeysStmt      *sql.Stmt
+}
+
+// nolint:unused
+func (s *keyBackupStatements) prepare(db *sql.DB) (err error) {
+	_, err = db.Exec(keyBackupTableSchema)
+	if err != nil {
+		return
+	}
+	if s.insertBackupKeyStmt, err = db.Prepare(insertBackupKeySQL); err != nil {
+		return
+	}
+	if s.updateBackupKeyStmt, err = db.Prepare(updateBackupKeySQL); err != nil {
+		return
+	}
+	if s.countKeysStmt, err = db.Prepare(countKeysSQL); err != nil {
+		return
+	}
+	if s.selectKeysStmt, err = db.Prepare(selectKeysSQL); err != nil {
+		return
+	}
+	return
+}
+
+func (s keyBackupStatements) countKeys(
+	ctx context.Context, txn *sql.Tx, userID, version string,
+) (count int64, err error) {
+	err = txn.Stmt(s.countKeysStmt).QueryRowContext(ctx, userID, version).Scan(&count)
+	return
+}
+
+func (s *keyBackupStatements) insertBackupKey(
+	ctx context.Context, txn *sql.Tx, userID, version string, key api.InternalKeyBackupSession,
+) (err error) {
+	_, err = txn.Stmt(s.insertBackupKeyStmt).ExecContext(
+		ctx, userID, key.RoomID, key.SessionID, version, key.FirstMessageIndex, key.ForwardedCount, key.IsVerified, string(key.SessionData),
+	)
+	return
+}
+
+func (s *keyBackupStatements) updateBackupKey(
+	ctx context.Context, txn *sql.Tx, userID, version string, key api.InternalKeyBackupSession,
+) (err error) {
+	_, err = txn.Stmt(s.updateBackupKeyStmt).ExecContext(
+		ctx, key.FirstMessageIndex, key.ForwardedCount, key.IsVerified, string(key.SessionData), userID, key.RoomID, key.SessionID, version,
+	)
+	return
+}
+
+func (s *keyBackupStatements) selectKeys(
+	ctx context.Context, txn *sql.Tx, userID, version string,
+) (map[string]map[string]api.KeyBackupSession, error) {
+	result := make(map[string]map[string]api.KeyBackupSession)
+	rows, err := txn.Stmt(s.selectKeysStmt).QueryContext(ctx, userID, version)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeysStmt.Close failed")
+	for rows.Next() {
+		var key api.InternalKeyBackupSession
+		// room_id, session_id, first_message_index, forwarded_count, is_verified, session_data
+		var sessionDataStr string
+		if err := rows.Scan(&key.RoomID, &key.SessionID, &key.FirstMessageIndex, &key.ForwardedCount, &key.IsVerified, &sessionDataStr); err != nil {
+			return nil, err
+		}
+		key.SessionData = json.RawMessage(sessionDataStr)
+		roomData := result[key.RoomID]
+		if roomData == nil {
+			roomData = make(map[string]api.KeyBackupSession)
+		}
+		roomData[key.SessionID] = key.KeyBackupSession
+		result[key.RoomID] = roomData
+	}
+	return result, nil
+}

userapi/storage/accounts/postgres/key_backup_version_table.go

@@ -33,6 +33,7 @@ CREATE TABLE IF NOT EXISTS account_e2e_room_keys_versions (
     version BIGINT DEFAULT nextval('account_e2e_room_keys_versions_seq'),
     algorithm TEXT NOT NULL,
     auth_data TEXT NOT NULL,
+	etag TEXT NOT NULL,
     deleted SMALLINT DEFAULT 0 NOT NULL
 );
 
@@ -40,16 +41,19 @@ CREATE UNIQUE INDEX IF NOT EXISTS account_e2e_room_keys_versions_idx ON account_
 `
 
 const insertKeyBackupSQL = "" +
-	"INSERT INTO account_e2e_room_keys_versions(user_id, algorithm, auth_data) VALUES ($1, $2, $3) RETURNING version"
+	"INSERT INTO account_e2e_room_keys_versions(user_id, algorithm, auth_data, etag) VALUES ($1, $2, $3, $4) RETURNING version"
 
-const updateKeyBackupAuthDataSQL = "" + // TODO: do we need to WHERE algorithm = $3 as well?
+const updateKeyBackupAuthDataSQL = "" +
 	"UPDATE account_e2e_room_keys_versions SET auth_data = $1 WHERE user_id = $2 AND version = $3"
 
+const updateKeyBackupETagSQL = "" +
+	"UPDATE account_e2e_room_keys_versions SET etag = $1 WHERE user_id = $2 AND version = $3"
+
 const deleteKeyBackupSQL = "" +
 	"UPDATE account_e2e_room_keys_versions SET deleted=1 WHERE user_id = $1 AND version = $2"
 
 const selectKeyBackupSQL = "" +
-	"SELECT algorithm, auth_data, deleted FROM account_e2e_room_keys_versions WHERE user_id = $1 AND version = $2"
+	"SELECT algorithm, auth_data, etag, deleted FROM account_e2e_room_keys_versions WHERE user_id = $1 AND version = $2"
 
 const selectLatestVersionSQL = "" +
 	"SELECT MAX(version) FROM account_e2e_room_keys_versions WHERE user_id = $1"
@@ -60,8 +64,10 @@ type keyBackupVersionStatements struct {
 	deleteKeyBackupStmt         *sql.Stmt
 	selectKeyBackupStmt         *sql.Stmt
 	selectLatestVersionStmt     *sql.Stmt
+	updateKeyBackupETagStmt     *sql.Stmt
 }
 
+// nolint:unused
 func (s *keyBackupVersionStatements) prepare(db *sql.DB) (err error) {
 	_, err = db.Exec(keyBackupVersionTableSchema)
 	if err != nil {
@@ -82,14 +88,17 @@ func (s *keyBackupVersionStatements) prepare(db *sql.DB) (err error) {
 	if s.selectLatestVersionStmt, err = db.Prepare(selectLatestVersionSQL); err != nil {
 		return
 	}
+	if s.updateKeyBackupETagStmt, err = db.Prepare(updateKeyBackupETagSQL); err != nil {
+		return
+	}
 	return
 }
 
 func (s *keyBackupVersionStatements) insertKeyBackup(
-	ctx context.Context, txn *sql.Tx, userID, algorithm string, authData json.RawMessage,
+	ctx context.Context, txn *sql.Tx, userID, algorithm string, authData json.RawMessage, etag string,
 ) (version string, err error) {
 	var versionInt int64
-	err = txn.Stmt(s.insertKeyBackupStmt).QueryRowContext(ctx, userID, algorithm, string(authData)).Scan(&versionInt)
+	err = txn.Stmt(s.insertKeyBackupStmt).QueryRowContext(ctx, userID, algorithm, string(authData), etag).Scan(&versionInt)
 	return strconv.FormatInt(versionInt, 10), err
 }
 
@@ -104,6 +113,17 @@ func (s *keyBackupVersionStatements) updateKeyBackupAuthData(
 	return err
 }
 
+func (s *keyBackupVersionStatements) updateKeyBackupETag(
+	ctx context.Context, txn *sql.Tx, userID, version, etag string,
+) error {
+	versionInt, err := strconv.ParseInt(version, 10, 64)
+	if err != nil {
+		return fmt.Errorf("invalid version")
+	}
+	_, err = txn.Stmt(s.updateKeyBackupETagStmt).ExecContext(ctx, etag, userID, versionInt)
+	return err
+}
+
 func (s *keyBackupVersionStatements) deleteKeyBackup(
 	ctx context.Context, txn *sql.Tx, userID, version string,
 ) (bool, error) {
@@ -124,7 +144,7 @@ func (s *keyBackupVersionStatements) deleteKeyBackup(
 
 func (s *keyBackupVersionStatements) selectKeyBackup(
 	ctx context.Context, txn *sql.Tx, userID, version string,
-) (versionResult, algorithm string, authData json.RawMessage, deleted bool, err error) {
+) (versionResult, algorithm string, authData json.RawMessage, etag string, deleted bool, err error) {
 	var versionInt int64
 	if version == "" {
 		err = txn.Stmt(s.selectLatestVersionStmt).QueryRowContext(ctx, userID).Scan(&versionInt)
@@ -137,7 +157,7 @@ func (s *keyBackupVersionStatements) selectKeyBackup(
 	versionResult = strconv.FormatInt(versionInt, 10)
 	var deletedInt int
 	var authDataStr string
-	err = txn.Stmt(s.selectKeyBackupStmt).QueryRowContext(ctx, userID, versionInt).Scan(&algorithm, &authDataStr, &deletedInt)
+	err = txn.Stmt(s.selectKeyBackupStmt).QueryRowContext(ctx, userID, versionInt).Scan(&algorithm, &authDataStr, &etag, &deletedInt)
 	deleted = deletedInt == 1
 	authData = json.RawMessage(authDataStr)
 	return

userapi/storage/accounts/postgres/storage.go

@@ -19,6 +19,7 @@ import (
 	"database/sql"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"strconv"
 	"time"
 
@@ -45,7 +46,8 @@ type Database struct {
 	accountDatas          accountDataStatements
 	threepids             threepidStatements
 	openIDTokens          tokenStatements
-	keyBackups            keyBackupVersionStatements
+	keyBackupVersions     keyBackupVersionStatements
+	keyBackups            keyBackupStatements
 	serverName            gomatrixserverlib.ServerName
 	bcryptCost            int
 	openIDTokenLifetimeMS int64
@@ -94,9 +96,13 @@ func NewDatabase(dbProperties *config.DatabaseOptions, serverName gomatrixserver
 	if err = d.openIDTokens.prepare(db, serverName); err != nil {
 		return nil, err
 	}
-	if err = d.keyBackups.prepare(db); err != nil {
+	/*
+		if err = d.keyBackupVersions.prepare(db); err != nil {
 			return nil, err
 		}
+		if err = d.keyBackups.prepare(db); err != nil {
+			return nil, err
+		} */
 
 	return d, nil
 }
@@ -377,7 +383,7 @@ func (d *Database) CreateKeyBackup(
 	ctx context.Context, userID, algorithm string, authData json.RawMessage,
 ) (version string, err error) {
 	err = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
-		version, err = d.keyBackups.insertKeyBackup(ctx, txn, userID, algorithm, authData)
+		version, err = d.keyBackupVersions.insertKeyBackup(ctx, txn, userID, algorithm, authData, "")
 		return err
 	})
 	return
@@ -387,7 +393,7 @@ func (d *Database) UpdateKeyBackupAuthData(
 	ctx context.Context, userID, version string, authData json.RawMessage,
 ) (err error) {
 	err = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
-		return d.keyBackups.updateKeyBackupAuthData(ctx, txn, userID, version, authData)
+		return d.keyBackupVersions.updateKeyBackupAuthData(ctx, txn, userID, version, authData)
 	})
 	return
 }
@@ -396,7 +402,7 @@ func (d *Database) DeleteKeyBackup(
 	ctx context.Context, userID, version string,
 ) (exists bool, err error) {
 	err = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
-		exists, err = d.keyBackups.deleteKeyBackup(ctx, txn, userID, version)
+		exists, err = d.keyBackupVersions.deleteKeyBackup(ctx, txn, userID, version)
 		return err
 	})
 	return
@@ -404,10 +410,101 @@ func (d *Database) DeleteKeyBackup(
 
 func (d *Database) GetKeyBackup(
 	ctx context.Context, userID, version string,
-) (versionResult, algorithm string, authData json.RawMessage, deleted bool, err error) {
+) (versionResult, algorithm string, authData json.RawMessage, etag string, deleted bool, err error) {
 	err = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
-		versionResult, algorithm, authData, deleted, err = d.keyBackups.selectKeyBackup(ctx, txn, userID, version)
+		versionResult, algorithm, authData, etag, deleted, err = d.keyBackupVersions.selectKeyBackup(ctx, txn, userID, version)
 		return err
 	})
 	return
 }
+
+// nolint:nakedret
+func (d *Database) UpsertBackupKeys(
+	ctx context.Context, version, userID string, uploads []api.InternalKeyBackupSession,
+) (count int64, etag string, err error) {
+	// wrap the following logic in a txn to ensure we atomically upload keys
+	err = sqlutil.WithTransaction(d.db, func(txn *sql.Tx) error {
+		_, _, _, oldETag, deleted, err := d.keyBackupVersions.selectKeyBackup(ctx, txn, userID, version)
+		if err != nil {
+			return err
+		}
+		if deleted {
+			return fmt.Errorf("backup was deleted")
+		}
+		// pull out all keys for this (user_id, version)
+		existingKeys, err := d.keyBackups.selectKeys(ctx, txn, userID, version)
+		if err != nil {
+			return err
+		}
+
+		changed := false
+		// loop over all the new keys (which should be smaller than the set of backed up keys)
+		for _, newKey := range uploads {
+			// if we have a matching (room_id, session_id), we may need to update the key if it meets some rules, check them.
+			existingRoom := existingKeys[newKey.RoomID]
+			if existingRoom != nil {
+				existingSession, ok := existingRoom[newKey.SessionID]
+				if ok {
+					if shouldReplaceRoomKey(existingSession, newKey.KeyBackupSession) {
+						err = d.keyBackups.updateBackupKey(ctx, txn, userID, version, newKey)
+						changed = true
+						if err != nil {
+							return err
+						}
+					}
+					// if we shouldn't replace the key we do nothing with it
+					continue
+				}
+			}
+			// if we're here, either the room or session are new, either way, we insert
+			err = d.keyBackups.insertBackupKey(ctx, txn, userID, version, newKey)
+			changed = true
+			if err != nil {
+				return err
+			}
+		}
+
+		count, err = d.keyBackups.countKeys(ctx, txn, userID, version)
+		if err != nil {
+			return err
+		}
+		if changed {
+			// update the etag
+			var newETag string
+			if oldETag == "" {
+				newETag = "1"
+			} else {
+				oldETagInt, err := strconv.ParseInt(oldETag, 10, 64)
+				if err != nil {
+					return fmt.Errorf("failed to parse old etag: %s", err)
+				}
+				newETag = strconv.FormatInt(oldETagInt+1, 10)
+			}
+			etag = newETag
+			return d.keyBackupVersions.updateKeyBackupETag(ctx, txn, userID, version, newETag)
+		} else {
+			etag = oldETag
+		}
+		return nil
+	})
+	return
+}
+
+// TODO FIXME XXX : This logic really shouldn't live in the storage layer, but I don't know where else is sensible which won't
+// create circular import loops
+func shouldReplaceRoomKey(existing, uploaded api.KeyBackupSession) bool {
+	// https://spec.matrix.org/unstable/client-server-api/#backup-algorithm-mmegolm_backupv1curve25519-aes-sha2
+	// "if the keys have different values for is_verified, then it will keep the key that has is_verified set to true"
+	if uploaded.IsVerified && !existing.IsVerified {
+		return true
+	}
+	// "if they have the same values for is_verified, then it will keep the key with a lower first_message_index"
+	if uploaded.FirstMessageIndex < existing.FirstMessageIndex {
+		return true
+	}
+	// "and finally, is is_verified and first_message_index are equal, then it will keep the key with a lower forwarded_count"
+	if uploaded.ForwardedCount < existing.ForwardedCount {
+		return true
+	}
+	return false
+}

userapi/storage/accounts/sqlite3/key_backup_table.go

@@ -0,0 +1,134 @@
+// 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 sqlite3
+
+import (
+	"context"
+	"database/sql"
+	"encoding/json"
+
+	"github.com/matrix-org/dendrite/internal"
+	"github.com/matrix-org/dendrite/userapi/api"
+)
+
+const keyBackupTableSchema = `
+CREATE TABLE IF NOT EXISTS account_e2e_room_keys (
+    user_id TEXT NOT NULL,
+    room_id TEXT NOT NULL,
+    session_id TEXT NOT NULL,
+
+    version TEXT NOT NULL,
+    first_message_index INTEGER NOT NULL,
+    forwarded_count INTEGER NOT NULL,
+    is_verified BOOLEAN NOT NULL,
+    session_data TEXT NOT NULL
+);
+CREATE UNIQUE INDEX IF NOT EXISTS e2e_room_keys_idx ON account_e2e_room_keys(user_id, room_id, session_id);
+`
+
+const insertBackupKeySQL = "" +
+	"INSERT INTO account_e2e_room_keys(user_id, room_id, session_id, version, first_message_index, forwarded_count, is_verified, session_data) " +
+	"VALUES ($1, $2, $3, $4, $5, $6, $7, $8)"
+
+const updateBackupKeySQL = "" +
+	"UPDATE account_e2e_room_keys SET first_message_index=$1, forwarded_count=$2, is_verified=$3, session_data=$4 " +
+	"WHERE user_id=$5 AND room_id=$6 AND session_id=$7 AND version=$8"
+
+const countKeysSQL = "" +
+	"SELECT COUNT(*) FROM account_e2e_room_keys WHERE user_id = $1 AND version = $2"
+
+const selectKeysSQL = "" +
+	"SELECT room_id, session_id, first_message_index, forwarded_count, is_verified, session_data FROM account_e2e_room_keys " +
+	"WHERE user_id = $1 AND version = $2"
+
+type keyBackupStatements struct {
+	insertBackupKeyStmt *sql.Stmt
+	updateBackupKeyStmt *sql.Stmt
+	countKeysStmt       *sql.Stmt
+	selectKeysStmt      *sql.Stmt
+}
+
+// nolint:unused
+func (s *keyBackupStatements) prepare(db *sql.DB) (err error) {
+	_, err = db.Exec(keyBackupTableSchema)
+	if err != nil {
+		return
+	}
+	if s.insertBackupKeyStmt, err = db.Prepare(insertBackupKeySQL); err != nil {
+		return
+	}
+	if s.updateBackupKeyStmt, err = db.Prepare(updateBackupKeySQL); err != nil {
+		return
+	}
+	if s.countKeysStmt, err = db.Prepare(countKeysSQL); err != nil {
+		return
+	}
+	if s.selectKeysStmt, err = db.Prepare(selectKeysSQL); err != nil {
+		return
+	}
+	return
+}
+
+func (s keyBackupStatements) countKeys(
+	ctx context.Context, txn *sql.Tx, userID, version string,
+) (count int64, err error) {
+	err = txn.Stmt(s.countKeysStmt).QueryRowContext(ctx, userID, version).Scan(&count)
+	return
+}
+
+func (s *keyBackupStatements) insertBackupKey(
+	ctx context.Context, txn *sql.Tx, userID, version string, key api.InternalKeyBackupSession,
+) (err error) {
+	_, err = txn.Stmt(s.insertBackupKeyStmt).ExecContext(
+		ctx, userID, key.RoomID, key.SessionID, version, key.FirstMessageIndex, key.ForwardedCount, key.IsVerified, string(key.SessionData),
+	)
+	return
+}
+
+func (s *keyBackupStatements) updateBackupKey(
+	ctx context.Context, txn *sql.Tx, userID, version string, key api.InternalKeyBackupSession,
+) (err error) {
+	_, err = txn.Stmt(s.updateBackupKeyStmt).ExecContext(
+		ctx, key.FirstMessageIndex, key.ForwardedCount, key.IsVerified, string(key.SessionData), userID, key.RoomID, key.SessionID, version,
+	)
+	return
+}
+
+func (s *keyBackupStatements) selectKeys(
+	ctx context.Context, txn *sql.Tx, userID, version string,
+) (map[string]map[string]api.KeyBackupSession, error) {
+	result := make(map[string]map[string]api.KeyBackupSession)
+	rows, err := txn.Stmt(s.selectKeysStmt).QueryContext(ctx, userID, version)
+	if err != nil {
+		return nil, err
+	}
+	defer internal.CloseAndLogIfError(ctx, rows, "selectKeysStmt.Close failed")
+	for rows.Next() {
+		var key api.InternalKeyBackupSession
+		// room_id, session_id, first_message_index, forwarded_count, is_verified, session_data
+		var sessionDataStr string
+		if err := rows.Scan(&key.RoomID, &key.SessionID, &key.FirstMessageIndex, &key.ForwardedCount, &key.IsVerified, &sessionDataStr); err != nil {
+			return nil, err
+		}
+		key.SessionData = json.RawMessage(sessionDataStr)
+		roomData := result[key.RoomID]
+		if roomData == nil {
+			roomData = make(map[string]api.KeyBackupSession)
+		}
+		roomData[key.SessionID] = key.KeyBackupSession
+		result[key.RoomID] = roomData
+	}
+	return result, nil
+}

userapi/storage/accounts/sqlite3/key_backup_version_table.go

@@ -31,6 +31,7 @@ CREATE TABLE IF NOT EXISTS account_e2e_room_keys_versions (
     version INTEGER PRIMARY KEY AUTOINCREMENT,
     algorithm TEXT NOT NULL,
     auth_data TEXT NOT NULL,
+	etag TEXT NOT NULL,
     deleted INTEGER DEFAULT 0 NOT NULL
 );
 
@@ -38,16 +39,19 @@ CREATE UNIQUE INDEX IF NOT EXISTS account_e2e_room_keys_versions_idx ON account_
 `
 
 const insertKeyBackupSQL = "" +
-	"INSERT INTO account_e2e_room_keys_versions(user_id, algorithm, auth_data) VALUES ($1, $2, $3) RETURNING version"
+	"INSERT INTO account_e2e_room_keys_versions(user_id, algorithm, auth_data, etag) VALUES ($1, $2, $3, $4) RETURNING version"
 
-const updateKeyBackupAuthDataSQL = "" + // TODO: do we need to WHERE algorithm = $3 as well?
+const updateKeyBackupAuthDataSQL = "" +
 	"UPDATE account_e2e_room_keys_versions SET auth_data = $1 WHERE user_id = $2 AND version = $3"
 
+const updateKeyBackupETagSQL = "" +
+	"UPDATE account_e2e_room_keys_versions SET etag = $1 WHERE user_id = $2 AND version = $3"
+
 const deleteKeyBackupSQL = "" +
 	"UPDATE account_e2e_room_keys_versions SET deleted=1 WHERE user_id = $1 AND version = $2"
 
 const selectKeyBackupSQL = "" +
-	"SELECT algorithm, auth_data, deleted FROM account_e2e_room_keys_versions WHERE user_id = $1 AND version = $2"
+	"SELECT algorithm, auth_data, etag, deleted FROM account_e2e_room_keys_versions WHERE user_id = $1 AND version = $2"
 
 const selectLatestVersionSQL = "" +
 	"SELECT MAX(version) FROM account_e2e_room_keys_versions WHERE user_id = $1"
@@ -58,8 +62,10 @@ type keyBackupVersionStatements struct {
 	deleteKeyBackupStmt         *sql.Stmt
 	selectKeyBackupStmt         *sql.Stmt
 	selectLatestVersionStmt     *sql.Stmt
+	updateKeyBackupETagStmt     *sql.Stmt
 }
 
+// nolint:unused
 func (s *keyBackupVersionStatements) prepare(db *sql.DB) (err error) {
 	_, err = db.Exec(keyBackupVersionTableSchema)
 	if err != nil {
@@ -80,14 +86,17 @@ func (s *keyBackupVersionStatements) prepare(db *sql.DB) (err error) {
 	if s.selectLatestVersionStmt, err = db.Prepare(selectLatestVersionSQL); err != nil {
 		return
 	}
+	if s.updateKeyBackupETagStmt, err = db.Prepare(updateKeyBackupETagSQL); err != nil {
+		return
+	}
 	return
 }
 
 func (s *keyBackupVersionStatements) insertKeyBackup(
-	ctx context.Context, txn *sql.Tx, userID, algorithm string, authData json.RawMessage,
+	ctx context.Context, txn *sql.Tx, userID, algorithm string, authData json.RawMessage, etag string,
 ) (version string, err error) {
 	var versionInt int64
-	err = txn.Stmt(s.insertKeyBackupStmt).QueryRowContext(ctx, userID, algorithm, string(authData)).Scan(&versionInt)
+	err = txn.Stmt(s.insertKeyBackupStmt).QueryRowContext(ctx, userID, algorithm, string(authData), etag).Scan(&versionInt)
 	return strconv.FormatInt(versionInt, 10), err
 }
 
@@ -102,6 +111,17 @@ func (s *keyBackupVersionStatements) updateKeyBackupAuthData(
 	return err
 }
 
+func (s *keyBackupVersionStatements) updateKeyBackupETag(
+	ctx context.Context, txn *sql.Tx, userID, version, etag string,
+) error {
+	versionInt, err := strconv.ParseInt(version, 10, 64)
+	if err != nil {
+		return fmt.Errorf("invalid version")
+	}
+	_, err = txn.Stmt(s.updateKeyBackupETagStmt).ExecContext(ctx, etag, userID, versionInt)
+	return err
+}
+
 func (s *keyBackupVersionStatements) deleteKeyBackup(
 	ctx context.Context, txn *sql.Tx, userID, version string,
 ) (bool, error) {
@@ -122,7 +142,7 @@ func (s *keyBackupVersionStatements) deleteKeyBackup(
 
 func (s *keyBackupVersionStatements) selectKeyBackup(
 	ctx context.Context, txn *sql.Tx, userID, version string,
-) (versionResult, algorithm string, authData json.RawMessage, deleted bool, err error) {
+) (versionResult, algorithm string, authData json.RawMessage, etag string, deleted bool, err error) {
 	var versionInt int64
 	if version == "" {
 		err = txn.Stmt(s.selectLatestVersionStmt).QueryRowContext(ctx, userID).Scan(&versionInt)
@@ -135,7 +155,7 @@ func (s *keyBackupVersionStatements) selectKeyBackup(
 	versionResult = strconv.FormatInt(versionInt, 10)
 	var deletedInt int
 	var authDataStr string
-	err = txn.Stmt(s.selectKeyBackupStmt).QueryRowContext(ctx, userID, versionInt).Scan(&algorithm, &authDataStr, &deletedInt)
+	err = txn.Stmt(s.selectKeyBackupStmt).QueryRowContext(ctx, userID, versionInt).Scan(&algorithm, &authDataStr, &etag, &deletedInt)
 	deleted = deletedInt == 1
 	authData = json.RawMessage(authDataStr)
 	return

userapi/storage/accounts/sqlite3/storage.go

@@ -19,6 +19,7 @@ import (
 	"database/sql"
 	"encoding/json"
 	"errors"
+	"fmt"
 	"strconv"
 	"sync"
 	"time"
@@ -43,7 +44,8 @@ type Database struct {
 	accountDatas          accountDataStatements
 	threepids             threepidStatements
 	openIDTokens          tokenStatements
-	keyBackups            keyBackupVersionStatements
+	keyBackupVersions     keyBackupVersionStatements
+	keyBackups            keyBackupStatements
 	serverName            gomatrixserverlib.ServerName
 	bcryptCost            int
 	openIDTokenLifetimeMS int64
@@ -98,9 +100,13 @@ func NewDatabase(dbProperties *config.DatabaseOptions, serverName gomatrixserver
 	if err = d.openIDTokens.prepare(db, serverName); err != nil {
 		return nil, err
 	}
-	if err = d.keyBackups.prepare(db); err != nil {
+	/*
+		if err = d.keyBackupVersions.prepare(db); err != nil {
 			return nil, err
 		}
+		if err = d.keyBackups.prepare(db); err != nil {
+			return nil, err
+		} */
 
 	return d, nil
 }
@@ -418,7 +424,7 @@ func (d *Database) CreateKeyBackup(
 	ctx context.Context, userID, algorithm string, authData json.RawMessage,
 ) (version string, err error) {
 	err = d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
-		version, err = d.keyBackups.insertKeyBackup(ctx, txn, userID, algorithm, authData)
+		version, err = d.keyBackupVersions.insertKeyBackup(ctx, txn, userID, algorithm, authData, "")
 		return err
 	})
 	return
@@ -428,7 +434,7 @@ func (d *Database) UpdateKeyBackupAuthData(
 	ctx context.Context, userID, version string, authData json.RawMessage,
 ) (err error) {
 	err = d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
-		return d.keyBackups.updateKeyBackupAuthData(ctx, txn, userID, version, authData)
+		return d.keyBackupVersions.updateKeyBackupAuthData(ctx, txn, userID, version, authData)
 	})
 	return
 }
@@ -437,7 +443,7 @@ func (d *Database) DeleteKeyBackup(
 	ctx context.Context, userID, version string,
 ) (exists bool, err error) {
 	err = d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
-		exists, err = d.keyBackups.deleteKeyBackup(ctx, txn, userID, version)
+		exists, err = d.keyBackupVersions.deleteKeyBackup(ctx, txn, userID, version)
 		return err
 	})
 	return
@@ -445,10 +451,102 @@ func (d *Database) DeleteKeyBackup(
 
 func (d *Database) GetKeyBackup(
 	ctx context.Context, userID, version string,
-) (versionResult, algorithm string, authData json.RawMessage, deleted bool, err error) {
+) (versionResult, algorithm string, authData json.RawMessage, etag string, deleted bool, err error) {
 	err = d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
-		versionResult, algorithm, authData, deleted, err = d.keyBackups.selectKeyBackup(ctx, txn, userID, version)
+		versionResult, algorithm, authData, etag, deleted, err = d.keyBackupVersions.selectKeyBackup(ctx, txn, userID, version)
 		return err
 	})
 	return
 }
+
+// nolint:nakedret
+func (d *Database) UpsertBackupKeys(
+	ctx context.Context, version, userID string, uploads []api.InternalKeyBackupSession,
+) (count int64, etag string, err error) {
+	// wrap the following logic in a txn to ensure we atomically upload keys
+	err = d.writer.Do(d.db, nil, func(txn *sql.Tx) error {
+		_, _, _, oldETag, deleted, err := d.keyBackupVersions.selectKeyBackup(ctx, txn, userID, version)
+		if err != nil {
+			return err
+		}
+		if deleted {
+			return fmt.Errorf("backup was deleted")
+		}
+		// pull out all keys for this (user_id, version)
+		existingKeys, err := d.keyBackups.selectKeys(ctx, txn, userID, version)
+		if err != nil {
+			return err
+		}
+
+		changed := false
+		// loop over all the new keys (which should be smaller than the set of backed up keys)
+		for _, newKey := range uploads {
+			// if we have a matching (room_id, session_id), we may need to update the key if it meets some rules, check them.
+			existingRoom := existingKeys[newKey.RoomID]
+			if existingRoom != nil {
+				existingSession, ok := existingRoom[newKey.SessionID]
+				if ok {
+					if shouldReplaceRoomKey(existingSession, newKey.KeyBackupSession) {
+						err = d.keyBackups.updateBackupKey(ctx, txn, userID, version, newKey)
+						changed = true
+						if err != nil {
+							return err
+						}
+					}
+					// if we shouldn't replace the key we do nothing with it
+					continue
+				}
+			}
+			// if we're here, either the room or session are new, either way, we insert
+			err = d.keyBackups.insertBackupKey(ctx, txn, userID, version, newKey)
+			changed = true
+			if err != nil {
+				return err
+			}
+		}
+
+		count, err = d.keyBackups.countKeys(ctx, txn, userID, version)
+		if err != nil {
+			return err
+		}
+		if changed {
+			// update the etag
+			var newETag string
+			if oldETag == "" {
+				newETag = "1"
+			} else {
+				oldETagInt, err := strconv.ParseInt(oldETag, 10, 64)
+				if err != nil {
+					return fmt.Errorf("failed to parse old etag: %s", err)
+				}
+				newETag = strconv.FormatInt(oldETagInt+1, 10)
+			}
+			etag = newETag
+			return d.keyBackupVersions.updateKeyBackupETag(ctx, txn, userID, version, newETag)
+		} else {
+			etag = oldETag
+		}
+
+		return nil
+	})
+	return
+}
+
+// TODO FIXME XXX : This logic really shouldn't live in the storage layer, but I don't know where else is sensible which won't
+// create circular import loops
+func shouldReplaceRoomKey(existing, uploaded api.KeyBackupSession) bool {
+	// https://spec.matrix.org/unstable/client-server-api/#backup-algorithm-mmegolm_backupv1curve25519-aes-sha2
+	// "if the keys have different values for is_verified, then it will keep the key that has is_verified set to true"
+	if uploaded.IsVerified && !existing.IsVerified {
+		return true
+	}
+	// "if they have the same values for is_verified, then it will keep the key with a lower first_message_index"
+	if uploaded.FirstMessageIndex < existing.FirstMessageIndex {
+		return true
+	}
+	// "and finally, is is_verified and first_message_index are equal, then it will keep the key with a lower forwarded_count"
+	if uploaded.ForwardedCount < existing.ForwardedCount {
+		return true
+	}
+	return false
+}