Key exposure free chameleon hash schemes based on discrete logarithm problem

Abstract

A chameleon hash scheme is a trapdoor collision-resistant hash scheme, and it provides many interesting features in signature schemes with hash-and-sign construction. In this paper, we introduce the notion of key exposure threshold τ for a chameleon hash scheme for which a key exposure free chameleon hash scheme can be understood as the case with τ=∞. We propose chameleon hash schemesCHτ with the key exposure threshold τ based on discrete logarithm problem (DLP). For τ<∞, the proposed scheme is noninteractive and key exposure free as long as k ephemeral trapdoors are disclosed for k<τ. The proposed schemeCH∞ is a key exposure free chameleon hash scheme based on DLP, and it requires a label directory that can be managed by a third party. This improves the only known efficient key exposure free chameleon hash scheme based on DLP, which requires one interaction with the trapdoor holder. © 2012 John Wiley & Sons, Ltd..