Patent ID: 7917764

Claim:
A signature generation apparatus for performing a digital signature operation with use of a signature key, comprising: a key storage unit storing therein the signature key; a signature generation unit operable to perform the digital signature operation on signature target data with the use of the signature key to generate signature data; a counter unit operable to count a cumulative count of digital signature operations having been performed by the signature generation unit with the use of the signature key; a judgment unit operable to judge whether the cumulative count has reached a predetermined count; and a signature inhibition unit operable to, in a case where the judgment unit determines that the cumulative count has reached the predetermined count, inhibit the use of the signature key in the digital signature operation from then onward, wherein the signature inhibition unit generates a different signature key and overwrites the signature key stored in the key storage unit with the different signature key to inhibit the use of the signature key in the digital signature operation, wherein the signature generation apparatus further comprises: a verification key certificate storage unit storing therein a verification key certificate including (i) a verification key corresponding to the signature key and (ii) verification key signature data indicating authenticity of the verification key and which is generated by a 1 st private key; a public key certificate storage unit storing therein a public key certificate including (i) a public key corresponding to the 1 st private key and (ii) public key signature data indicating authenticity of the public key and which is generated by a 2 nd private key held by an outside functional entity; and a transmission unit operable to transmit the signature target data, the signature data generated by the signature generation unit, the verification key certificate, and the public key certificate to a signature verification apparatus that performs a verification of the signature data, and wherein the signature inhibition unit, in order to inhibit the use of the signature key in the digital signature operation, (i) generates a different verification key that corresponds to the different signature key, (ii) generates different verification key signature data for the different verification key using the 1 st private key, (iii) generates a different verification key certificate that includes the different verification key and the different verification key signature data, and (iv) overwrites the verification key certificate stored in the public key certificate storage unit with the different verification key certificate.