A Multi-Policies Threshold Signature Scheme with Group Verifiability

The multi-policies threshold signature is very practical in the research of signature. In this kind of scheme, multiple secret keys are shared among a group of users, and each secret key has its specific threshold value. Moreover, the secret keys corresponding to different threshold values can be used to sign documents depending on their significance. However, all current multi-polices threshold signature schemes cannot deal with the group verifiability. In order to solve this problem, a group-verifiable multi-polices threshold signature scheme is proposed in this paper. In the presented scheme, the group verifiability can be realized and the property of the traceable multi-polices threshold signature keeps unchanged. Namely, not only the threshold values of the signing group but also the threshold values of the verifiable group can change with the secure classifications of the signing documents. In the process of verifiability, the threshold values of the verifiable group depend on the significance of the documents. The main merit is that the signing group and the verifiable group can swap their roles. Therefore, the two groups can sign and verify each other, i.e., it is a two-way signing and verifying scheme. The analysis shows that the proposed scheme is also secure and practical.