# Utilizing Blockchain for IoT Privacy through Enhanced ECIES with Secure Hash Function
## 2 Related Works
### Blockchain Mechanisms for IoT Security  
Blockchain-based frameworks to preserve user privacy in IoT have been proposed in a majority of works. The authors of [30] proposed a blockchain-based data acquisition scheme for a secure collection of data from IoT devices using Unmanned Aerial Vehicles (UAVs). This solution was researched by collecting data from IoT devices using UAV and storing safely in blockchain through mobile edge computing. However, in this approach, the required verification increases the latency. The researchers in [31] enhanced privacy in IoT with the Hyperledger Fabric Blockchain framework and Attribute Based Access Control (ABAC) to ensure efficient access control even under large number of requests in the IoT environment. The performance of this approach is analysed using two terminals which may increase the computational cost. The authors of [5] enhanced the publish/subscribe model with a blockchain-based secure publish/subscribe system to protect the privacy of publishers and subscribers. This model uses the Ethereum platform to ensure identity protection of the publisher and subscriber, using public key encryption with an equality test to guarantee the confidentiality of IoT data transmitted in the blockchain network. Though the authors present a promising way to preserve privacy in IoT system, the use of Diffie-Hellman protocol for encryption procedure does not resist security attack, causing the user to compromise the security of their personal data. Based on consortium blockchain, the security and privacy in IoT were enhanced in [32] with a novel attribute-based access control scheme. This scheme avoids the need to maintain an access control list in the IoT system as compared to traditional access control technologies. The access policies are made up of attributes and stored in the form of transaction in the blockchain. The performance analysis of their system shows storage overhead increases linearly with an increase in the number of attributes, whereas the computation overhead is also linear in the number of attributes. The security analysis shows that their scheme provides resistance to various security attacks in the IoT system. However, the key pair developed for authentication of the transaction does not boost the security strength of the encrypted transactions. In [14], the authors enhanced user privacy preservation in the IoT system with a novel secure mutual authentication system to provide traceability and privacy protection of access policy and user consent. The use of ECIES protects the confidentiality and privacy of request transaction message and response data that is transmitted to obtain necessary consents before data transmission in IoT. It gives a correlation coefficient of 0.34499 between constructed request transactions and encrypted transaction with a computation time of 102.733 ms. The ECIES is implemented to generate the public/private keys for encrypting and decrypting the request transaction data and response data. However, keys generated from the publicly exposed point on the elliptic curve result in violating user privacy. A major concern regarding the adoption of blockchain technology in IoT networks is the enormous energy consumption associated with blockchains. This perception inevitably raises concerns about the further adoption of this technology, a fact that inhibits rapid uptake of what is widely considered to be a ground-breaking and disruptive innovation [33]. This fact, along with the significant increase in energy consumption caused by IoT networks has created a new challenge and diverted the focus towards creating an eco-friendlier IoT ecosystem, which provides energy efficient services and enables the production and use of renewable energy [34]. The combination of blockchains and a green IoT is focused on reducing energy consumption and adopting renewable resources rather than on energy generated by fossil fuels.