This document discusses security and efficiency challenges with sharing data in the cloud. It notes that while cloud computing allows easy storage and sharing of data, this exposes user data to security attacks. When data is shared in the cloud, cryptographic and authentication techniques are needed to protect user data. Mechanisms for sharing data must also be efficient so they do not reduce cloud service performance or waste resources. The document reviews several existing approaches for secure and efficient data sharing in cloud computing and their limitations, noting the need for improved techniques that can handle multiple users and owners dynamically sharing data.