# Comparative Study of Blockchain Hashing Algorithms with a Proposal for HashLEA
## 3 Background  
### Blockchain Technology and IoT Applications  
The IoT intends to connect devices to the Internet in a peer-to-peer pattern for efficient data collection and sharing in our daily lives. Blockchain has been integrated with the IoT to resolve the obtainable IoT problems. Blockchain technology has been broadly used in IoT applications. In contrast to the other similar technologies--which keep data and information in central locations--data and information with blockchain technology will be reserved inside secure loops in the network. Thus, this process can enhance the level of security of the information. Unlike centralized technologies, blockchain decentralizes data storage, making unauthorized access or hacking more difficult and almost impossible. The high capability of blockchain to encrypt and protect data contributes to the heightened security of information [46]. Traditional systems often lack transparency regarding the location, storage, and transmission of private data. Thus, when blockchain technology is applied, it will record all the data and communications that occur between the consumer and the producer. It will also let him know the information he wants to know. This will reflect positively on increasing and enhancing the reliability between the two parties. For example, highly secure transfers can be achieved by the implementation of blockchain technology services, which are activated by the principle of payment first. Thus, the decentralized storage networks of blockchain facilitate secure fund transfers and transactions with reliability [47]. A centralized server/client paradigm is used in most IoT solutions, where, through the Internet, clients are connected to the servers hosted in the cloud, and this can be costly to maintain. Even though these solutions are capable of working successfully, as IoT grows, a new paradigm is considered necessary. The proposed decentralized solutions with a P2P pattern cannot guarantee security and privacy [48]. Blockchain has the latent qualities or abilities to answer a lot of the challenges that arise from the usage of IoT [49]:  
* The centralized server/client IoT solutions that are hosted in the cloud can be costly to maintain. * Maintaining millions of distributed smart devices is considered a significant challenge. * Transparency is crucial for safety and trust. It is recommended that open-source solutions be employed and evaluated in the context of the next generation of IoT devices. * Usually, the IoT needs a central entity, so at any point in which a failure occurs, it will be prominent. Managing aspects such as time synchronization, registries, privacy, and trust on a continuous basis will be challenging. Blockchain applied to IoT has three big challenges [50]:
* Scalability issues: as the size of the blockchain grows with the increase and growth of transactions, there are concerns about scalability and potential centralization. * Computing power and time constraints: IoT devices are low on processing power and consume low energy; therefore, it is difficult to use secure encryption algorithms, which may take too long to process. * Storage challenges: All nodes in a blockchain keep a copy of all dealings or transactions that have ever happened in the blockchain since its formation. The size will become greater, leading to potential storage issues over time. IoT devices may face limitations in storing large amounts of data. The challenges for blockchain as applied to IoT begin with low resources. Despite the fact that the processing power of most IoT devices is low, optimization of the algorithms in these devices enables certain operations. The cryptographic operations are the most processing-demanding operations in blockchain; testing and optimizing hash functions for IoT devices are essential to ensure performance feasibility [51]. Many companies and industries are now using specific sensors for their IoT applications to control the operations of managing the company's affairs and monitor the time that these operations take.