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Top1. Introduction
Cloud computing provides on-demand services like servers, storage, applications, networking resources etc. to the users by connecting tons of computing resources together. Among these services, cloud storage is a new network-based data storage technique which can be used for data outsourcing at reduced operational cost and this stored data can be accessed at any time anywhere quiet easily through any device connected to the Internet (Ren et al., 2012). In spite of these benefits, users are sometimes reluctant to adopt it because of inherent security issues. Therefore, to address these issues data is stored in the encrypted form over an untrusted server (Kamara and Lauter, 2010) but at the same time encryption eliminates searching capability for the data owner. Hence, the concept of searchable encryption (SE) comes into play. SE enables a third-party cloud server to perform keyword-based search over encrypted data on behalf of the data user without asking for the secret key. SE allows search over encrypted data if the data user provides a search trapdoor for that particular keyword to the third-party cloud server. Searchable encryption schemes (Gupta et al., 2016; Yu et al., 2018; Zheng et al., 2018; Yu et al., 2018) have been developed for both symmetric and asymmetric encryption settings. If symmetric key setting is used for the construction of searchable encryption, then it is known as symmetric searchable encryption (SSE) (Song et al., 2000; Goh et al., 2003; Agrawal et al., 2004; Curtmola et al., 2011). In multi-user setting SSE suffers from the complicated process of key sharing, i.e. each sender must get a secret key before encrypting the message for the intended recipient. In order to make this process simple the idea of using the public-key setting was first proposed by Boneh et al. (2004) and is known as public key encryption with keyword search (PEKS). PEKS enables data encryption by any user who can see the public key of the recipient, thus provides flexibility. So, public-key setting is the preferable choice for searchable encryption. After this, many searchable encryption schemes were developed in public key setting using techniques like identity-based encryption (Abdalla et al., 2005; Wu et al., 2017a; Lu et al., 2017) and attribute-based encryption (Sun et al., 2016; Han et al., 2017; Miao et al., 2016; Fan et al., 2018). In this paper, the identity-based encryption is used for the construction of proposed searchable encryption scheme.