Fair Partially Blind Signatures

It is well-known that blind signature schemes provide full anonymity for the receiving user. For many real-world applications, however, this leaves too much room for fraud. There are two generalizations of blind signature schemes that compensate this weakness: fair blind signatures and partially blind signatures. Fair blind signature schemes allow a trusted third party to revoke blindness in case of a dispute. In partially blind signature schemes, the signer retains a certain control over the signed message because signer and user have to agree on a specific part of the signed message. In this work, we unify the previous well-studied models into a generalization, called fair partially blind signatures. We propose an instantiation that is secure in the standard model without any setup assumptions. With this construction, we also give a positive answer to the open question of whether fair blind signature schemes in the standard model exist.