R-OO-KASE: Revocable Online/Offline Key Aggregate Searchable Encryption

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R‑OO‑KASE: Revocable Online/Offline Key Aggregate Searchable Encryption Mukti Padhya1   · Devesh C. Jinwala1 Received: 31 October 2019 / Revised: 30 January 2020 / Accepted: 16 July 2020 © The Author(s) 2020

Abstract The existing Key Aggregate Searchable Encryption (KASE) schemes allow searches on the encrypted dataset using a single query trapdoor, with a feature to delegate the search rights of multiple files using a constant size key. However, the operations required to generate the ciphertext and decrypt it in these schemes incur higher computational costs, due to the computationally expensive pairing operations in encryption/decryption. This makes the use of such schemes in resource-constrained devices, such as Radio Frequency Identification Devices, Wireless Sensor Network nodes, Internet of Things nodes, infeasible. Motivated with the goal to reduce the computational cost, in this paper, we propose a Revocable Online/Offline KASE (R-OO-KASE) scheme, based on the idea of splitting the encryption/decryption operations into two distinct phases: online and offline. The offline phase computes the majority of costly operations when the device is on an electrical power source. The online phase generates final output with the minimal computational cost when the message (or ciphertext) and keywords become known. In addition, the proposed scheme R-OO-KASE also offers multi-keyword search capability and allows the data owners to revoke the delegated rights at any point in time, the two features are not supported in the existing schemes. The security analysis and empirical evaluations show that the proposed scheme is efficient to use in resource-constrained devices and provably secure as compared to the existing KASE schemes. Keywords  Searchable encryption · Data sharing · Data retrieval · Cloud server · Multi-keyword search · Online/offline encryption · Revocation Mathematics Subject Classification  94A60 · 68P25

1 Introduction Cloud computing services are often resorted to, with an aim to reduce the overhead of data management and data processing at the user side. However, when the data are outsourced and stored on a remote cloud, it is often desired to encrypt the same in order to protect the data from unauthorized access. One of the issues associated with encryption is that the accessibility and usability of encrypted data are definitely lowered since the latter would require the decryption of data before being put to use. There are two distinct threads of research pursued in the literature with respect to addressing this issue of improving the usability of the * Mukti Padhya [email protected] 1



Department of Computer Engineering, Sardar Vallabhbhai National Institute of Technology (SVNIT), Surat, India

encrypted data viz. (1) carrying out arbitrary computations on the encrypted data using homomorphic encryption [8] or (2) devising operation by which the encrypted data can, at least, be searched for the desired keyword value, to be present or not. Our focus in this paper is on the latter, i.e., on Search