diff --git a/backend/mpc-system/api/grpc/coordinator/v1/session_coordinator.pb.go b/backend/mpc-system/api/grpc/coordinator/v1/session_coordinator.pb.go
index dfba0e56..08fc72db 100644
--- a/backend/mpc-system/api/grpc/coordinator/v1/session_coordinator.pb.go
+++ b/backend/mpc-system/api/grpc/coordinator/v1/session_coordinator.pb.go
@@ -519,6 +519,7 @@ type JoinSessionResponse struct {
 	Success       bool                   `protobuf:"varint,1,opt,name=success,proto3" json:"success,omitempty"`
 	SessionInfo   *SessionInfo           `protobuf:"bytes,2,opt,name=session_info,json=sessionInfo,proto3" json:"session_info,omitempty"`
 	OtherParties  []*PartyInfo           `protobuf:"bytes,3,rep,name=other_parties,json=otherParties,proto3" json:"other_parties,omitempty"`
+	PartyIndex    int32                  `protobuf:"varint,4,opt,name=party_index,json=partyIndex,proto3" json:"party_index,omitempty"` // This party's assigned index
 	unknownFields protoimpl.UnknownFields
 	sizeCache     protoimpl.SizeCache
 }
@@ -574,6 +575,13 @@ func (x *JoinSessionResponse) GetOtherParties() []*PartyInfo {
 	return nil
 }
 
+func (x *JoinSessionResponse) GetPartyIndex() int32 {
+	if x != nil {
+		return x.PartyIndex
+	}
+	return 0
+}
+
 // SessionInfo contains session information
 type SessionInfo struct {
 	state         protoimpl.MessageState `protogen:"open.v1"`
@@ -1541,11 +1549,13 @@ const file_api_proto_session_coordinator_proto_rawDesc = "" +
 	"\n" +
 	"join_token\x18\x03 \x01(\tR\tjoinToken\x12?\n" +
 	"\vdevice_info\x18\x04 \x01(\v2\x1e.mpc.coordinator.v1.DeviceInfoR\n" +
-	"deviceInfo\"\xb7\x01\n" +
+	"deviceInfo\"\xd8\x01\n" +
 	"\x13JoinSessionResponse\x12\x18\n" +
 	"\asuccess\x18\x01 \x01(\bR\asuccess\x12B\n" +
 	"\fsession_info\x18\x02 \x01(\v2\x1f.mpc.coordinator.v1.SessionInfoR\vsessionInfo\x12B\n" +
-	"\rother_parties\x18\x03 \x03(\v2\x1d.mpc.coordinator.v1.PartyInfoR\fotherParties\"\xcc\x01\n" +
+	"\rother_parties\x18\x03 \x03(\v2\x1d.mpc.coordinator.v1.PartyInfoR\fotherParties\x12\x1f\n" +
+	"\vparty_index\x18\x04 \x01(\x05R\n" +
+	"partyIndex\"\xcc\x01\n" +
 	"\vSessionInfo\x12\x1d\n" +
 	"\n" +
 	"session_id\x18\x01 \x01(\tR\tsessionId\x12!\n" +