New Types of Verifiably Encrypted Signature Schemes

A verifiably encrypted signature scheme involves a signer, a verifier, and an adjudicator. It can convince a verifier that a given ciphertext is an encryption of signature on a given message. At a later stage on agreed or in case of dispute, the adjudicator can extract and give the signer's signature to the verifier. In existing verifiably encrypted signatures, the adjudicator is assumed to be a trusted third party who will not conspire with either of the two parties involved. Obviously, this assumption is naive. In this paper, we propose two new types of verifiably encrypted signature schemes. They can resolve the problem that the adjudicator may collaborate with the verifier. We also analyze the security of the proposed schemes.