Analysis and Improvement of a Proxy Blind Multi-signature Scheme without a Secure Channel

Proxy blind signature is a cryptographic research hotspot, and has been applied in many occasions. Many proxy blind signature schemes were proposed, however, all the schemes rely on secure channels to transmit proxy secret key. Therefore, Lu, Cao and Zhou proposed a new proxy blind multi-signature scheme recently, which does not need a secure channel and is provably secure under the random oracle model. In this letter, however, we show that their scheme is not secure against the original signer´s forgery attack. Moreover, we give four improved proxy key generation algorithms to counter this attack.