Abstract
Cloud data storage and sharing services are now becoming very popular. However, there are also security risks that may compromise the data stored on the cloud and shared over the cloud. In this talk, I will first make a security analysis of three cloud storage services Dropbox, Google Drive, and Microsoft SkyDrive, and demonstrate all three services have security weaknesses that may result in data leakage without users' awareness. After that, I present a fine-grained access control mechanism for sharing encrypted cloud data. The new mechanism supports secure cloud data sharing without the assumption of trust on cloud service providers, and also provides effective user revocation.