Recent technological advances have sparked the popularity and success of cloud. This new paradigm is gaining an expanding interest, since it provides cost ecient architectures that support the transmission, storage, and intensive computing of data. However, these promising storage services bring many challenging design issues, considerably due to both loss of data control and abstract nature of clouds. The objective of this survey is to provide a consistent view about both data security concerns and privacy issues that are faced by clients in cloud storage environments. This survey brings a critical comparative analysis of cryptographic defense mechanisms, and beyond this, it explores research directions and technology trends to address the protection of outsourced data in cloud infrastructures