Patent ID: 8495362

Claim:
A signature system that is structured such that said signature system includes a public key certificate obtainment device, a public key certificate issuance device, a signature device, a signature verification device, and a tracing device, wherein said public key certificate obtainment device inputs item data and an infrastructure public key that includes an item key that is an element corresponding to each item of said item data and outputs both a public key certificate including item data and a secret key using said data that have been input and data supplied from said public key certificate issuance device, wherein said public key certificate issuance device inputs an infrastructure public key that includes the item key that is the element corresponding to each item of the item data and outputs a proof that will be used to identify a signer using said data that have been input and the data supplied from said public key certificate obtainment device, wherein said signature device inputs a message, a revelation item set that represents items to be revealed, the secret key and the public key certificate that said public key certificate obtainment device has output and outputs a selectively anonymous signature corresponding to said message and revelation item data that are item data that belong to said revelation item set using said data that have been input, wherein said signature verification device inputs both the selectively anonymous signature and the revelation item data that said signature device has output and verifies said selectively anonymous signature using said data that have been input, and wherein said tracing device inputs the selectively anonymous signature that said signature device has output and a secret key for tracing used to decrypt an encryption text of a part of a proof included in said selectively anonymous signature and outputs the part of said proof and decryption validity certification that is information that identifies said selectively anonymous signature using said data that have been input.