Designated-verifier proxy signature schemes
"In a proxy signature scheme, a user delegates his/her signing capability to another user in such a way that the latter can sign messages on behalf of the former. In this paper, we first propose a provably secure proxy signature scheme, which is based on a two-party Schnorr signature scheme. Then, we extend this basic scheme into designated-verifier proxy signatures (DVPS). More specifically, we get two versions of DVPS: weak DVPS and strong DVPS. In both versions, the validity of a proxy signature can be checked only by the designated verifier. In a weak DVPS scheme, however, the designated verifier can further convert such proxy signatures into public verifiable ones, while a strong DVPS scheme does not have the same property even if the designated verifier's secret key is revealed willingly or unwillingly. In addition, we briefly discuss some potential applications for DVPS."