  The increasing adoption of Cloud storage poses a number of privacy issues.
Users wish to preserve full control over their sensitive data and cannot accept
that it to be accessible by the remote storage provider. Previous research was
made on techniques to protect data stored on untrusted servers; however we
argue that the cloud architecture presents a number of open issues. To handle
them, we present an approach where confidential data is stored in a highly
distributed database, partly located on the cloud and partly on the clients.
Data is shared in a secure manner using a simple grant-and-revoke permission of
shared data and we have developed a system test implementation, using an
in-memory RDBMS with row-level data encryption for fine-grained data access
control
