Analysis and Improvement of a Threshold Signature Scheme Based on the General Access Structure

AbstractHua-wang Qin et al. proposed a novel threshold signature scheme based on the general access structure in order to break the applied limitation of the conventional threshold signature schemes. The security of the scheme was analyzed in this paper, and it is pointed out that the scheme is insecure because it cannot withstand conspiracy attacks and what's more, the identity of signer cannot be investigated. To overcome these security vulnerabilities, this paper proposed an improved threshold signature scheme, and the security analysis results show that the improved scheme can not only resist the conspiracy attack, but also have the properties of anonymity and traceability simultaneously

On-Line/Off-Line Threshold Proxy Re-Signature Scheme through the Simulation Approach

On-line/off-line threshold proxy re-signatures can efficiently improve the the performance of threshold proxy re-signature schemes. A simulation theorem for on-line/off-line threshold proxy re-signature schemes is presented in this paper. This theorem provides a theoretical basis for constructing an on-line/off-line threshold proxy re-signature scheme through the simulation approach, where the security of an on-line/off-line threshold proxy re-signature scheme can be reduced to that of its underlying divisible online/ off-line proxy re-signature scheme. Furthermore, we propose an on-line/off-line threshold proxy re-signature scheme which is proven secure (unforgeable and robust) under the computational Diffie-Hellman assumption and the discrete logarithm assumption. The on-line phase of the proposed scheme is efficient: computing a re-signature does not require any heavy computations such as exponentiations or pairings