Practical Constructions to Multiple Designated Confirmer Signatures

Designated confirmer signatures, initially introduced by Chaum in 1994, eliminated the undeniable signature shortcoming in which the signature can only be verified through the cooperation of the original signer. This paper proposes several practical constructions to multiple designated confirmer signature schemes. We employ the messagedependent proof of equality of the discrete logarithm and trap-door commitments to construct a new type of multiple confirmer scheme, where specified verifiers designated by the signer would have an advantage in verifying a signature where only one (out of n) confirmer is needed for a confirmation. Other verifiers, who the signer did not designate, must ask all n confirmers to collaboratively confirm this signature. This paper also provides an efficient and practical solution in applying the threshold functions on the designated confirmer signatures.