3-Multi Ranked Encryption with Enhanced Security in Cloud Computing

Searchable Encryption (SE) enables data owners to search remotely stored ciphertexts selectively. A practical model that is closest to real life should be able to handle search queries with multiple keywords and multiple data owners/users, and even return the top-k most relevant search results when requested. We refer to a model that satisfies all of the conditions a 3-multi ranked search model. However, SE schemes that have been proposed to date use fully trusted trapdoor generation centers, and several methods assume a secure connection between the data users and a trapdoor generation center. That is, they assume the trapdoor generation center is the only entity that can learn the information regarding queried keywords, but it will never attempt to use it in any other manner than that requested, which is impractical in real life. In this study, to enhance the security, we propose a new 3-multi ranked SE scheme that satisfies all conditions without these security assumptions. The proposed scheme uses randomized keywords to protect the interested keywords of users from both outside adversaries and the honest-but-curious trapdoor generation center, thereby preventing attackers from determining whether two different queries include the same keyword. Moreover, we develop a method for managing multiple encrypted keywords from every data owner, each encrypted with a different key. Our evaluation demonstrates that, despite the trade-off overhead that results from the weaker security assumption, the proposed scheme achieves reasonable performance compared to extant schemes, which implies that our scheme is practical and closest to real life.