A broadcast receiving system is disclosed that verifies a current digital certificate extracted from a digital broadcast signal using a previous digital certificate previously stored as trusted. The current and previous digital certificates are associated with digital signatures with which data received with the broadcast signal has been signed. Also disclosed is a system for signing application data to be broadcast together with a digital certificate in a digital broadcast signal. A current digital certificate attesting the validity of a digital signature attached to broadcast data is in turn signed with a digital signature using one or more previous private keys associated with respective previous certificates identifying the issuer of the current digital certificate. These disclosures are in particular applicable to HbbTV.