A broadcast receiving system comprising a receiver for receiving a digital broadcast signal and a processor configured to: extract a current digital certificate from the broadcast signal, wherein the current digital certificate has been digitally signed with one or more private keys associated with respective previous digital certificates issued by the issuer of the current certificate; and verify the current digital certificate extracted from the digital broadcast signal using a previous digital certificate previously stored as trusted by verifying the extracted digital certificate using a respective public key associated with the previous digital certificate stored as trusted, wherein the current and previous digital certificates are associated with digital signatures with which data transmitted with the broadcast signal has been signed, wherein the processor is configured to: - make a first determination before verifying the current digital certificate of whether the extracted current digital certificate has previously been stored as trusted; if the first determination is negative, make a second determination of whether a previous digital certificate issued by the issuer has been stored as trusted; if the second determination is positive, use the previously stored trusted digital certificate to make a third determination of whether the extracted current certificate is valid by verifying the extracted current digital certificate using a respective public key associated with the previously stored trusted digital certificate; and if the third determination is positive, store the extracted current digital certificate as trusted. extract a current digital certificate from the broadcast signal, wherein the current digital certificate has been digitally signed with one or more private keys associated with respective previous digital certificates issued by the issuer of the current certificate; and verify the current digital certificate extracted from the digital broadcast signal using a previous digital certificate previously stored as trusted by verifying the extracted digital certificate using a respective public key associated with the previous digital certificate stored as trusted, wherein the current and previous digital certificates are associated with digital signatures with which data transmitted with the broadcast signal has been signed, wherein the processor is configured to: - make a first determination before verifying the current digital certificate of whether the extracted current digital certificate has previously been stored as trusted; - make a first determination before verifying the current digital certificate of whether the extracted current digital certificate has previously been stored as trusted; if the first determination is negative, make a second determination of whether a previous digital certificate issued by the issuer has been stored as trusted; if the second determination is positive, use the previously stored trusted digital certificate to make a third determination of whether the extracted current certificate is valid by verifying the extracted current digital certificate using a respective public key associated with the previously stored trusted digital certificate; and if the third determination is positive, store the extracted current digital certificate as trusted.