Security requirements for data storage services on public clouds

Nowadays, cloud computing is a consolidated technology and users are taking all their data to the cloud. Security and privacy are strongly required by users who are concerned about their data being exposed. Cryptography is one of the solutions to avoid unauthorized access to data, but with so many cloud service providers, can users trust them the safety of their data? How safe are they? In this paper we present an analysis of security features of some cloud service providers and point out some problems. Moreover, we propose a set of requirements for a privacy oriented cloud service and make recommendations to improve the security and privacy offered by new and existing providers.