Designated Confirmer Signatures With Unified Verification
After the introduction of Designated Confirmer Signatures (DCS) by Chaum in 1994, considerable researches have been done to build generic schemes from standard digital signatures and construct efficient concrete solutions. In DCS schemes, a signature cannot be verified without the help of either the signer or a semi-trusted third party, called the designated confirmer. If necessary, the confirmer can further convert a DCS into an ordinary signature that is publicly verifiable. However, there is one limit in most existing schemes: the signer is not given the ability to disavow invalid DCS signatures.