In this paper, a new quantum encryption based on the key-controlled chained CNOT operations, which is named KCCC encryption, is proposed. With the KCCC encryption, an improved arbitrated quantum signature (AQS) protocol is presented. Compared with the existing protocols, our protocol can effectively prevent forgery attacks and disavowal attacks. Moreover, only single state is required in the protocol. We hope it is helpful to further research in the design of AQS protocols in future.