Abstract: We propose a forgery attack on a proxy blind signature scheme proposed by Tan et al. By using the forgery attack, a dishonest original signer can forge the proxy signing key and produce valid proxy blind signatures. By successfully identifying the forgery attack, we show that their scheme is insecure. Furthermore, to improve Tan et al's scheme, we propose an improved proxy blind signature scheme.

Key words: security analysis, proxy blind signature, proxy signature, digital signature