Cryptanalysis of Okamoto Blind Signature Scheme and Partially Blind Signature Scheme

Recently, Okamoto proposed a signature scheme without random oracles and its variant, and then constructed a blind signature scheme and a partially blind signature scheme without random oracles based on the variant scheme. He also provided security proof for each signature scheme. However, in this paper, the author shows that the variant scheme and the (partially) blind signature scheme are not all secure, anyone who do not query the signing oracle can forge signature of any message.