## 3 Related Work
### Problem Statement  
The problems identified from previous research works are expanded in this section. An access control scheme and a user credibility incentive mechanism was proposed in [44] called LBAC. The designed Hyperledger Fabric operates in three parallel phases, and the phases are execute, order and validate. The certificate authority (CA) initializes at first; then the attribute authority (AA) submits the attribute to the blockchain. A further attribute token was generated using the set of attributes of the user which is then allowed for storage or access into the Cloud Service Provider (CSP). In this work, meta-data were stored in the blockchain, whereas the whole data were stored in the CSP. The meta-data from the DO consists of a symmetric key in cipher text and a hash value of data in cipher text. Hence, it performs proxy re-encryption, i.e., pre-decryption in the blockchain and final decryption for the CSP data. In [45], Device Contract (DC), Policy Contract (PC) and Access Contract (AC) were proposed. These three contracts define the development of an attribute-based access control (ABAC) model, an ABAC policy and resource management. The defined policy can be updated and deleted in the blockchain. The major problems stated in these works are illustrated in the following,  
* An IoT environment deals with a massive number of devices; hence data arrive in a short time period. The decryption requires IoT devices, which are actually computation-constrained devices, to utilize scarce resources. * User data are not protected during storage that causes alteration of data, since the data can be sensitive and data privacy is essential. * In this work, the admin has rights to modify, add or delete the policy contract, but the admin was not authenticated.If the admin is compromised, the contracts will be altered in favor of the illegitimate user's requirements. * The blockchain technology uses the SHA-256 algorithm for hashing which is also used in this work. It is not a lightweight hashing algorithm; hence it is difficult with massive numbers of IoT devices. In [46], an HLF Blockchain was proposed using the performance of local authentication of client devices. A multi-layer architecture network is designed, and the layers are IoT devices, cluster heads, base station and data storage (server). A client, i.e., an IoT device and server communication, was established with a hello packet. It then exchanges a key using the Diffie-Hellman algorithm. The authentication takes place by exchanging the challenge-response that was generated by the client itself, and during authentication, the response was validated at the server side. The basic research issues in this proposed work are,  
* The performance of authentication using a challenge-response is generated by the client; in case the client is not legitimate, it can interrupt the system. This is the only validation that is performed to guarantee a client. The response computation at the server side is simpler using a single predefined mathematical operator. * The local authentication between the client and server fails to consider the unique security credential of the client. In [47], an access tree was constructed and managed by the authority node (AN). The access tree was created from the chaincode that defines the credentials of requesters. The ECC algorithm was applied for key generation which is used as the identity of the device. The device's credentials such as identity, public key, access policy, IP address, group identity, access history and attribute library are used for validation of device accounts. Then the device creates an access policy which is further converted into a collaboration access tree using the access for each device provided. The problems identified from this work are illustrated below. * In this work, if the request is not satisfied by the access tree in the authority node, then the access tree is reconstructed. This increases time consumption due to re-construction of trees.