A Secure Nominative Proxy Signature Scheme for Distributed Shared Object Systems

------------------------------------------------------------------ABSTRACT----------------------------------------------------------------Digital signature scheme is an important research topic in cryptography. An ordinary digital signature scheme allows a signer to create signatures of documents and the generated signatures can be verified by any person. A proxy signature scheme, a variation of ordinary digital signature scheme, enables a proxy signer to sign messages on behalf of the original signer. To be used in different applications, many proxy signatures schemes were proposed. Among them, Soe and Lee nominative Proxy Signature scheme, and Jianhong Zhang, Jianhong Zou, and Yumin Wang nominative Proxy Signature scheme for mobile communication. The authors of these schemes argued that their schemes satisfies the following security requirements: user anonymity, authentication and non-repudiation. However, in this paper, we show that their schemes do not satisfy the non-repudiation among their security requirements. And then we propose a new nominative proxy signature scheme that solves the weakness of their schemes. Unlike their schemes, the proposed scheme provides a non-repudiation property and moreover it is more secure than their schemes.