Abstract Batch verification is a method to verify multiple digital signatures at a batch in time less than total individual verification time. Batch verification for an identity‐based signature scheme (IBS) is attractive because a short public identity such as an e‐mail address can be used as a verification key. In this paper, we first review the recent IBS scheme proposed by Shim and its batch verifier to show that the batch verifier is vulnerable to a forgery attack. In order to resist to the attack, we propose a new efficient batch verifier for the IBS scheme. The proposed batch verifier can deal with arbitrary number of signatures as a batch. We prove formally that the proposed batch verifier is secure. Then, we analyze the computation cost of the proposed batch verifier using concrete parameters and compare it with well‐known batch verifiers. The comparison shows that our batch verifier can significantly outperform the existing batch verifiers in computation. We finally present a one‐round three‐party identity‐based key agreement protocol as an application of our batch verifier, which requires only three pairing operations in verification. Copyright © 2015 John Wiley & Sons, Ltd.

The controllable linkability of group signatures introduced by Hwanget al.enables an entity who has a linking key to find whether or not two group signatures were generated by the same signer, while preserving the anonymity. This functionality is very useful in many applications that require the linkability but still need the anonymity, such as sybil attack detection in a vehicular ad hoc network and privacy-preserving data mining. In this paper, we present a new group signature scheme supporting the controllable linkability. The major advantage of this scheme is that the signature length is very short, even shorter than this in the best-known group signature scheme without supporting the linkability. We have implemented our scheme in both a Linux machine with an Intel Core2 Quad and an iPhone4. We compare the results with a number of existing group signature schemes. We also prove security features of our scheme, such as anonymity, traceability, nonframeability, and linkability, under a random oracle model.

This paper presents a new bit-parallel multiplier for the finite field GF(2/sup m/) defined by an irreducible all-one polynomial. In order to reduce the complexity of the multiplier, we introduce a redundant representation and use the well-known multiplication method proposed by Karatsuba. The main idea is to combine the redundant representation and the Karatsuba method to design an efficient bit-parallel multiplier. As a result, the proposed multiplier requires about 25 percent fewer AND/XOR gates than the previously proposed multipliers using an all-one polynomial, while it has almost the same time delay as the previously proposed ones.