Nowadays, ubiquitous sensor devices such as mobile phones, laptops, GPSes, etc. allow one to access not only his own data but also others' on cloud servers. To enhance security, data is usually encrypted before sending to the servers. However, making use of others' ones encrypted data without decryption keys is very challenging. In this paper, we suggest a framework that allows users of cloud-based social networks to share their private data in a secure manner. In our framework, every user in a group has his own secret key to encrypt and decrypt data. The key will be revoked if the user leaves the group. Using proxy re-encryption schemes, the framework helps any user be able to access others' data in the same group.
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