## 3 Related Work
The key exchange algorithm was not applicable to sign signatures; thus, it is vulnerable to a man-in-middle attack. In [37], the authors proposed an ABAC with authorized search scheme (EACAS); then an attribute-based encryption is used to ensure secure data. The major entities that are involved in this system model are data owner, data user and cloud server. The EACAS operates consecutively as system setup, key generation, encryption, trapdoor generation, data search and reverse of encryption. The attributes were hidden based partially on the conversion of the cipher text. Then the access trees were constructed using AND and OR gates during which user access was provided. The increase in policies will also increase the length of the tree. A device access control scheme was proposed for the IoT, and it was known in short as DACS-IoT [38]. A one-way cryptographic hash function, i.e., SHA-1 and ECC algorithm, was proposed in this work. Initially, the user identity was verified followed by a certificate check and then a signature verification check. This verification was carried out between two smart devices, before data transmission. The ECC algorithm was weak in the selection of the curve. An ABAC scheme was carried out by the following steps of system initialization, registration, address creation, attribute request and access control [39]. The device has a unique identity and an address. This address was created by hashing the public key and identity using a concatenation operator. Then the hashed address was signed in attribute authority which will be updated in a Merkle tree that is present in the blockchain. During registration, identity-based cryptography is used to verify identities; however, this is not sufficiently secure since identities are basic credentials that can be forged. Two concepts of ABAC and identity-based signature (IBS) were presented in [40]. The designed architecture performs four steps as system setup, request control, point decision point (PDP) and point enforcement point (PEP) execution. The PDP consists of an identity device, a request number, a decision and a signature. On the other hand, PEP is composed of the identity, decision and signed identity and signature. Based on the access request, the access decision was evaluated for each user. However, the identity was not a secure constraint; hence it can be eavesdropped on easily by attackers. A blockchain-aided searchable attribute-based encryption (BC-SABE) that was decentralized using a blockchain was proposed [41]. The designed coalition blockchain enables creation of partial tokensfor users. This system model is composed of four main entities such as data owner, data user, blockchain and cloud. The sequential processes are system initialization, registration, revocation, key generation, encryption, token generation, search and decryption. The user attribute set was validated with respect to the access structure, and then the search results are returned. The access validation in blockchain was performed one after the other which consumes time for processing. A blockchain-enabled decentralized capability access control, i.e., BlendCAC was discussed in this paper [42]. The BlendCAC architecture is comprised ofthe data user, the data owner and the blockchain network. Initially, in registration, the public and private keys were generated, and the identity was verified for authentication. A virtual identity (VID) was also developed. Then, according to the process of access control, a capability token was generated, and the policy decision was performed to give access to the user. An attribute-based framework was proposed to provide access control and communication control (ABAC-CC) [43]. Communication was established between the devices to the gateway, gateway to gateway, gateway to cloud and cloud to cloud. The authentication of the devices was performed using the cryptographic keys and then followed by the access control based on the attributes.