Dennis Y. W. Liu
Nominative Signature: Application, Security Model and Construction
Since the introduction of nominative signature in 1996, there have been only a few schemes proposed and all of them have already been found flawed. In addition, there is no formal security model defined. Even more problematic, there is no convincing application proposed. Due to these problems, the research of nominative signature has almost stalled and it is unknown if a secure nominative signature scheme can be built or there exists an application for it. In this paper, we give positive answers to these problems. First, we illustrate that nominative signature is a better tool for building user certification systems which are originally believed to be best implemented using a universal designated-verifier signature. Second, we propose a formal definition and a rigorous set of adversarial models for nominative signature. Third, we show that Chaum's undeniable signature can be transformed efficiently to a nominative signature and prove its security.
An Efficient One-move Nominative Signature Scheme
A signer in a Nominative Signature (NS) scheme can arbitrarily choose a nominee, then jointly generate a signature in such a way that the signature can only be verified with the nominee's consent. NS is particularly useful in user certification systems. Currently, the only secure NS scheme available requires multi-round communications between the nominator and the nominee during signature generation. This implies that an NS-based user certification system requires a certification issuer to interact with a user using a complicated multi-round protocol for certificate issuance. It remains an open problem to construct an efficient and non-interactive NS scheme. In this paper, we solve this problem by proposing the first efficient one-move (i.e. non-interactive) NS scheme. In addition, we propose an enhanced security requirement called Strong Invisibility, and prove that our scheme satisfies this strong security requirement.