Cryptanalysis of a certificateless proxy signature and its extension to blind signature

Abstract

Recently, Tso et al. proposed a certificateless proxy signature scheme and extended it to a certificateless proxy blind signature scheme. They claimed that their schemes have the unforgeability property. However, in this paper, we show that their schemes are forgeable under the public key replacement attack. By substituting the public keys of an original signer and a proxy signer, the Type I adversary can forge the proxy delegation of the original signer and the proxy signature of the proxy signer on any message.