A New Undeniable Signature with Partially Inheritable Confirmation Ability

Abstract

The concept of undeniable signature was introduced by Chaum et al. in 1989 [CA89], where the signature can only be verified by cooperation with the signer. Two alternative schemes, the convertible undeniable signature [BCDP91] and the confirmer signature [Cha94], can overcome the shortcomings of the original undeniable signature that a signer should become unavailable or refuse to cooperate. However, a critical problem of these two schemes is no limitation to the verifiers. Once the signature is converted to a self-authentication signature (by the signer or confirmer), anyone can be convinced that the signature is correct. Moreover, in the confirmer signature scheme, the confirmer can immediately prove the validity of the signature to any verifier upon the signature being created; this means that the singer cannot flexibly control the time of delegating confirmation ability to the confirmer. Many applications require more precise design on the signer's control capability.

This paper will propose a new undeniable signature scheme that allows an additional party, called inheritor, to inherit the partial confirmation ability from the signer. Our scheme has the features that the signer can properly determine who can obtain the assurance from the inheritor that the signature is correct, and when the inheritor can acquire the confirmation ability. An inheritance key Kinh defined in our scheme is used to prevent the confirmation ability from being misused by the inheritor. The inheritor has no ability to prove the signature until he receives Kinh from the signer.