With the trend of networking and the growth of data value, networked storage security becomes hotpot of research. Aiming at the scalability and security requirement of massive storage system, we proposed a security storage service model combining storage mechanism and security policy and designed a set of scalable third-party security protocols. The protocols adopt public-key cryptography to guarantee the integrity of capability, avoiding the maintenance of shared key. The results of the formal analysis logically ensure the feasibility of the proposed security protocol. Furthermore, the overhead evaluation of the capability illustrates that the security protocol can meet the scalability requirement of storage system.