Re-encryption security model over outsourced cloud data Cloud computing is recommended as a promising technology, which delivers computational facilities as services to users over the Internet. As well as, the cloud computing brings significant risks for greater exposure to data security when users outsource sensitive data for sharing on cloud servers. To keep sensitive data confidentiality against untrusted cloud service provider, this paper discusses this challenging open issue using re-encryption scheme in outsourced cloud data. On the one hand, it allows the data owner to delegate most of the computation tasks to untrusted cloud servers providers without the need to have knowledge of the underlying plain texts. On the other hand, it employs double cryptographic methods to limit authorized users accessing updated cloud data with expired keys. This paper also obtains the restrictions of choosing appropriate encryption algorithm to establish secure re-encryption scheme in cloud data services.