diff --git a/federationapi/internal/perform.go b/federationapi/internal/perform.go
index 5a98cd218..61e1a949b 100644
--- a/federationapi/internal/perform.go
+++ b/federationapi/internal/perform.go
@@ -2,6 +2,7 @@ package internal
 
 import (
 	"context"
+	"crypto/ed25519"
 	"encoding/json"
 	"errors"
 	"fmt"
@@ -170,13 +171,24 @@ func (r *FederationInternalAPI) performJoinUsingServer(
 		UserIDQuerier: func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
 			return r.rsAPI.QueryUserIDForSender(ctx, roomID, senderID)
 		},
-		SenderIDCreator: func(ctx context.Context, userID spec.UserID, roomID spec.RoomID) (spec.SenderID, error) {
+		SenderIDCreator: func(ctx context.Context, userID spec.UserID, roomID spec.RoomID, roomVersion string) (spec.SenderID, ed25519.PrivateKey, error) {
+			// assign a roomNID, otherwise we can't create a private key for the user
+			_, nidErr := r.rsAPI.AssignRoomNID(ctx, roomID, gomatrixserverlib.RoomVersion(roomVersion))
+			if nidErr != nil {
+				return "", nil, nidErr
+			}
 			key, keyErr := r.rsAPI.GetOrCreateUserRoomPrivateKey(ctx, userID, roomID)
 			if keyErr != nil {
-				return "", keyErr
+				return "", nil, keyErr
 			}
-
-			return spec.SenderIDFromPseudoIDKey(key), nil
+			return spec.SenderIDFromPseudoIDKey(key), key, nil
+		},
+		StoreSenderIDFromPublicID: func(ctx context.Context, senderID spec.SenderID, userIDRaw string, roomID spec.RoomID) error {
+			storeUserID, userErr := spec.NewUserID(userIDRaw, true)
+			if userErr != nil {
+				return userErr
+			}
+			return r.rsAPI.StoreUserRoomPublicKey(ctx, senderID, *storeUserID, roomID)
 		},
 	}
 	response, joinErr := gomatrixserverlib.PerformJoin(ctx, r, joinInput)
diff --git a/federationapi/routing/join.go b/federationapi/routing/join.go
index b886382f7..f0784e604 100644
--- a/federationapi/routing/join.go
+++ b/federationapi/routing/join.go
@@ -15,6 +15,7 @@
 package routing
 
 import (
+	"context"
 	"fmt"
 	"net/http"
 	"sort"
@@ -113,6 +114,10 @@ func MakeJoin(
 		}
 	}
 
+	if senderID == "" {
+		senderID = spec.SenderID(userID.String())
+	}
+
 	input := gomatrixserverlib.HandleMakeJoinInput{
 		Context:           httpReq.Context(),
 		UserID:            userID,
@@ -224,6 +229,13 @@ func SendJoin(
 		UserIDQuerier: func(roomID spec.RoomID, senderID spec.SenderID) (*spec.UserID, error) {
 			return rsAPI.QueryUserIDForSender(httpReq.Context(), roomID, senderID)
 		},
+		StoreSenderIDFromPublicID: func(ctx context.Context, senderID spec.SenderID, userIDRaw string, roomID spec.RoomID) error {
+			userID, userErr := spec.NewUserID(userIDRaw, true)
+			if userErr != nil {
+				return userErr
+			}
+			return rsAPI.StoreUserRoomPublicKey(ctx, senderID, *userID, roomID)
+		},
 	}
 	response, joinErr := gomatrixserverlib.HandleSendJoin(input)
 	switch e := joinErr.(type) {
diff --git a/roomserver/api/api.go b/roomserver/api/api.go
index 5d7728bd4..ab56529c5 100644
--- a/roomserver/api/api.go
+++ b/roomserver/api/api.go
@@ -74,6 +74,7 @@ type RoomserverInternalAPI interface {
 type UserRoomPrivateKeyCreator interface {
 	// GetOrCreateUserRoomPrivateKey gets the user room key for the specified user. If no key exists yet, a new one is created.
 	GetOrCreateUserRoomPrivateKey(ctx context.Context, userID spec.UserID, roomID spec.RoomID) (ed25519.PrivateKey, error)
+	StoreUserRoomPublicKey(ctx context.Context, senderID spec.SenderID, userID spec.UserID, roomID spec.RoomID) error
 }
 
 type InputRoomEventsAPI interface {
@@ -235,7 +236,7 @@ type FederationRoomserverAPI interface {
 	QueryBulkStateContentAPI
 	QuerySenderIDAPI
 	UserRoomPrivateKeyCreator
-
+	AssignRoomNID(ctx context.Context, roomID spec.RoomID, roomVersion gomatrixserverlib.RoomVersion) (roomNID types.RoomNID, err error)
 	SigningIdentityFor(ctx context.Context, roomID spec.RoomID, senderID spec.UserID) (fclient.SigningIdentity, error)
 	// QueryServerBannedFromRoom returns whether a server is banned from a room by server ACLs.
 	QueryServerBannedFromRoom(ctx context.Context, req *QueryServerBannedFromRoomRequest, res *QueryServerBannedFromRoomResponse) error
diff --git a/roomserver/internal/api.go b/roomserver/internal/api.go
index 22ae23c80..2e12671ff 100644
--- a/roomserver/internal/api.go
+++ b/roomserver/internal/api.go
@@ -289,6 +289,15 @@ func (r *RoomserverInternalAPI) GetOrCreateUserRoomPrivateKey(ctx context.Contex
 	return key, nil
 }
 
+func (r *RoomserverInternalAPI) StoreUserRoomPublicKey(ctx context.Context, senderID spec.SenderID, userID spec.UserID, roomID spec.RoomID) error {
+	pubKeyBytes, err := senderID.RawBytes()
+	if err != nil {
+		return err
+	}
+	_, err = r.DB.InsertUserRoomPublicKey(ctx, userID, roomID, ed25519.PublicKey(pubKeyBytes))
+	return err
+}
+
 func (r *RoomserverInternalAPI) SigningIdentityFor(ctx context.Context, roomID spec.RoomID, senderID spec.UserID) (fclient.SigningIdentity, error) {
 	roomVersion, ok := r.Cache.GetRoomVersion(roomID.String())
 	if !ok {
@@ -307,7 +316,7 @@ func (r *RoomserverInternalAPI) SigningIdentityFor(ctx context.Context, roomID s
 		}
 		return fclient.SigningIdentity{
 			PrivateKey: privKey,
-			KeyID:      "ed25519",
+			KeyID:      "ed25519:1",
 			ServerName: "self",
 		}, nil
 	}
@@ -317,3 +326,7 @@ func (r *RoomserverInternalAPI) SigningIdentityFor(ctx context.Context, roomID s
 	}
 	return *identity, err
 }
+
+func (r *RoomserverInternalAPI) AssignRoomNID(ctx context.Context, roomID spec.RoomID, roomVersion gomatrixserverlib.RoomVersion) (roomNID types.RoomNID, err error) {
+	return r.DB.AssignRoomNID(ctx, roomID, roomVersion)
+}
diff --git a/roomserver/internal/perform/perform_create_room.go b/roomserver/internal/perform/perform_create_room.go
index 9316c1290..8c9656453 100644
--- a/roomserver/internal/perform/perform_create_room.go
+++ b/roomserver/internal/perform/perform_create_room.go
@@ -196,7 +196,7 @@ func (c *Creator) PerformCreateRoom(ctx context.Context, userID spec.UserID, roo
 		// sign all events with the pseudo ID key
 		identity = &fclient.SigningIdentity{
 			ServerName: "self",
-			KeyID:      "ed25519",
+			KeyID:      "ed25519:1",
 			PrivateKey: pseudoIDKey,
 		}
 	}
diff --git a/roomserver/internal/perform/perform_join.go b/roomserver/internal/perform/perform_join.go
index 3883a5b96..c14554640 100644
--- a/roomserver/internal/perform/perform_join.go
+++ b/roomserver/internal/perform/perform_join.go
@@ -314,7 +314,7 @@ func (r *Joiner) performJoinRoomByID(
 		// sign the event with the pseudo ID key
 		identity = fclient.SigningIdentity{
 			ServerName: "self",
-			KeyID:      "ed25519",
+			KeyID:      "ed25519:1",
 			PrivateKey: pseudoIDKey,
 		}
 	}