Provably secure partially blind signatures

Abstract

Partially blind signature schemes are an extension of blind signature schemes that allow a signer to explicitly include necessary information (expiration date, collateral conditions, or whatever) in the resulting signatures under some agreement with the receiver. This paper formalizes such a notion and presents secure and efficient schemes based on a widely applicable method of obtaining witness indistinguishable protocols. We then give a formal proof of security in the random oracle model. Our approach also allows one to construct secure fully blind signature schemes based on a variety of signature schemes.