Data security

There are a number of security threats associated with cloud data services, not only covering traditional security threats, e.g., network eavesdropping, illegal invasion, and denial of service attacks, but also including specific cloud computing threats, e.g., side channel attacks, virtualization vulnerabilities, and abuse of cloud services. To throttle the threats the following security requirements are to be met in a cloud data service.^[14]

Data Confidentiality

Data confidentiality is the property that data contents are not made available or disclosed to illegal users. Outsourced data is stored in a cloud and out of the owners' direct control. Only authorized users can access the sensitive data while others, including CSPs, should not gain any information of the data. Meanwhile, data owners expect to fully utilize cloud data services, e.g., data search, data computation, and data sharing, without the leakage of the data contents to CSPs or other adversaries.

Data Access Controllability

Access controllability means that a data owner can perform the selective restriction of access to his data outsourced to cloud. Legal users can be authorized by the owner to access the data, while others can not access it without permissions. Further, it is desirable to enforce fine-grained access control to the outsourced data, i.e., different users should be granted different access privileges with regard to different data pieces. The access authorization must be controlled only by the owner in untrusted cloud environments.

Data Integrity

Data integrity demands maintaining and assuring the accuracy and completeness of data. A data owner always expects that his data in a cloud can be stored correctly and trustworthily. It means that the data should not be illegally tampered, improperly modified, deliberately deleted, or maliciously fabricated. If any undesirable operations corrupt or delete the data, the owner should be able to detect the corruption or loss. Further, when a portion of the outsourced data is corrupted or lost, it can still be retrieved by the data users.