Security Analysis and their Improvement of Two Signature Schemes
Jianghong Zhang, Jianjun Xie · 2008
Recently, Wang et. al presented a short group signature scheme \cite{BX} without random oracles, and Kang \emph{et.al} gave an efficient ID-based strong designated verifier signature scheme \cite{WW}. And security proof of the two signature schemes were provided. Unfortunately, in this work we show that Wang \emph{et.al}'s group signature is universally forgeable, Namely, any one can forge a group signature on arbitrary message, then an improved vision is presented; And we also show that Kang \emph{et.al}'s scheme is forgeable, namely, a third party can produce a signature on arbitrary message $m$ by a given signature information. Finally, we give the corresponding attack on the two signature schemes.