Improvement of a Forward-Secure Ring Signature Scheme

In the regular ring signature, once the secret key is compromised, all signature before the compromise will not be trustworthy any more. Recently, to overcome the shortcomings, Wang et al. proposed a forward-secure ring signature scheme. However, in this paper, we show the scheme doesn´t satisfy the forward security. That is the adversary can forge the former signature if the signer´s current secret key is lost. Furthermore, based on Wang et al.´s scheme, we propose an improved forward-secure ring signature scheme.