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Data sharing is a main application of cloud computing.Some existing solutions are proposed to provide flexible access control for outsourced data in the cloud.However,few attentions have been paid to group-oriented data sharing when multiple data owners want to share their private data for cooperative purposes.In this paper,we put forward a new paradigm,referred to as secure,scalable and efficient multi-owner (SSEM) data sharing in clouds.The SSEM integrates identity-based encryption and asymmetric group key agreement to enable group-oriented access control for data owners in a many-to-many sharing patt.Moreover,with SSEM,users can join in or leave from the group conveniently with the privacy of both group data and user data.We proposed the key-ciphertext homomorphism technique to construct an SSEM scheme with short ciphertexts.The security analysis shows that our SSEM scheme achieves data security against unauthorized accesses and collusion attacks.Both theoretical and experimental results confirm that our proposed scheme takes users little costs to share and access outsourced data in a group manner.