Cloud services is a great opportunity for the users to enjoy the on-demand cloud applications without considering the local infrastructure limitations. Several schemes have been proposed for access control of outsourced data in cloud computing. Security is the primary obstacle that prevents the wide adoption of this promising computing model. Identity-based encryption (IBE) is the sender of a message can specify an identity such that only a receiver with matching identity can decrypt it. In the KP-ABE, a ciphertext is associated with a set of attributes, and a private key is associated with a monotonic tree, which describes this user’s identity. A user can decrypt the ciphertext if and only if the access tree in his private key is satisfied by the attributes in the ciphertext. However, the encrypter does not have entire control over the encryption policy. Furthermore, when a re-encryption occurs, all of the users in the same system must have their private keys re-issued so as to gain access to the re-encrypted files, and this process causes considerable problems in implementation. All problems and overhead are solved in the CP-ABE. In this, ciphertexts are created with an access structure, which specifies the encryption policy, and private keys are generated according to users’ attributes. A user can decrypt the ciphertext if and only if his attributes in the private key satisfy the access tree specified in the ciphertext. Hence the encrypter holds the encryption policy. Also, issued private keys will not be modified till the whole system reboots.