Informatica

Delegation of rights is a common practice in the real world. We present two identity-based threshold proxy signature schemes, which allow an original signer to delegate her signing capability to a group of n proxy signers, and it requires a consensus of t or more proxy signers in order to generate a valid signature. In addition to identity-based scheme, privacy protection for proxy singers and security assurance are two distinct features of this work. Our first scheme provides partial privacy protection to proxy signers such that all signers' identities are revealed, whereas none of those t participating signers is specified. On the other hand, all proxy signers remain anonymous in the second scheme. This provides a full privacy protection to all proxy signers; however, each valid signature contains a tag that allows one to trace all the participating proxy signers. Both our proposed schemes are secure against unforgeability under chosen message attack, and satisfy many other necessary conditions for proxy signature.

With rapid growth of mobile wireless networks, handheld devices are popularly used by people and many mobile applications have been rapidly developed. Considering the limited computing capability of smart cards or mobile devices, the security scheme design suitable for these mobile devices is a nontrivial challenge. A user authentication scheme is a mechanism to authenticate a remote user over an open network. In 2006, Das et al. proposed an identity (ID)-based remote user authentication scheme with smart cards using bilinear pairings. Unfortunately, their scheme is insecure against forgery attack. Recently, Giri and Srivastava proposed an improved scheme to overcome the forgery attack. The computational cost required by the Giri–Srivastava scheme is expensive, especially for smart cards with limited computing capability. In addition, the Giri–Srivastava scheme is unable to be used for a multi-server environment. This paper presents an efficient and secure ID-based remote user authentication scheme using bilinear pairings. Based on the computational Diffie–Hellman assumption, we show that the proposed scheme is secure against existential forgery on adaptively chosen-message and ID attack in the random oracle model. As compared with the recently proposed pairing-based authentication schemes, our scheme has better performance in term of the computational cost and it is suitable for a multi-server environment in distributed networks. Performance analysis and experimental data of related pairing operations on smartcards are given to demonstrate that our scheme is well suited for mobile devices with limited computing capability.

A key exchange (or agreement) protocol is designed to allow two entities establishing a session key to encrypt the communication data over an open network. In 1990, Gunther proposed an identity-based key exchange protocol based on the difficulty of computing a discrete logarithm problem. Afterwards, several improved protocols were proposed to reduce the number of communication steps and the communicational cost required by Gunther's protocol. This paper presents an efficient identity-based key exchange protocol based on the difficulty of computing a discrete logarithm problem. As compared with the previously proposed protocols, it has better performance in terms of the computational cost and the communication steps. The proposed key exchange protocol provides implicit key authentication as well as the desired security attributes of an authenticated key exchange protocol.

Recently, Tseng et al. proposed an improvement on Peyravian and Zunic's protected password transmission scheme and protected changing scheme to remove some security flaws. However, as we will point out in this paper, any adversary can intercept the request for changing the password sent by a legal user and modify it with a wrong password. Furthermore, we shall also propose an improved version of their protected password changing scheme to help it out of the trouble.

Smart card has been adopted to various applications. In 2000, Hwang and Li proposed a remote user authentication scheme, which is also using smart card. Nine months later, Chan and Cheng pointed out that there is a weakness in the remote authentication scheme proposed by Hwang and Li. In this paper, we show that Chan and Cheng's attack does not work well because they did not consider the format of user's identity. In addition, we propose several ways to solve the problem of Chan and Cheng's attack.