Cryptanalysis of a Certificateless Partially Blind Signature

Partially blind signature is an important technique in secure electronic cash system. Recently, Zhang et al. presented the first certificateless partially blind signature scheme and constructed an electronic cash system based on this scheme. They claimed that their certificateless partially blind signature scheme is secure in the random oracle model. However, in this paper, we demonstrate the scheme is not secure. Our attack indicates that a malicious KGC in the electronic cash system based on Zhang et al.'s certificateless partially blind signature can forge valid electronic coins without being detected by the bank. It will result in loss of the bank.