Auditing has vital significance in cloud computing,because data owners are afraid that their outsourced data will be lost or tempered.In current auditing schemes,the data owner stores its data and signatures together into the cloud,while the cloud server provides aggregated proof to the third-party auditor or the data owner,in ensuring that it correctly stores data.However,once the private key expires,the data owner will have to generate a new key,download all its data blocks and signatures,verify them using the old key,re-sign data blocks using the new key,and upload data blocks/new signatures.This will lead to high communication cost between the data owner and the cloud server,as well as high computation cost on the data owner.To address it,this paper introduces a novel key-changing and signature-updating scheme that permits the cloud server updating the signatures instead of the data owner.Finally,we prove our scheme to be secure under the random oracle model,and implement it on the OPENSTACK cloud platform.The results show that our scheme is secure and efficient.Especially,it reduces the communication and computation cost.