Remark on Shao et al.'s Bidirectional Proxy Re-signature Scheme in Indocrypt'07.
Kitae Kim, Ikkwon Yie, Seongan Lim · 2009
Recently, Shao et al. proposed two bidirectional proxy re-signature schemes Smb and Sid−mb [3]. In their paper, the authors gave security proofs to say that both of them are secure in their security model without random oracles. But, we found that the scheme Smb is miss leaded and its security proof is false. In this paper, we present an attack on Smb and improve it to be secure in their security model.