Cloud computing enables to reduce operating costs and maximize resource utilization. However, current cloud infrastructure is insufficient to guarantee the confidentiality of classified information for cloud users because one of administrators with privilege or remote hackers compromising management tools can leak the information. This paper addresses storage issues in cloud computing and proposes a secure storage service where stored user data are protected even against a malicious administrator and compromised software. We describe the architecture of proposed design and discuss the security issues of the design.