# Validating the Adoption of Heterogeneous Internet of Things with Blockchain
## 1 Introduction  
The importance of Internet of Things (IoT) has been demonstrated by the innovative and intelligent technologies and services that it can provide. It is composed of numerous physical objects that are linked to the Internet and are able to communicate with each other. These objects eventually generate a massive amount of data and thereby gather and broadcast them into information systems and technologies such as the cloud, Service-oriented Architecture (SoA), and workflow management system. The integrated technologies have proven their effectiveness in enhancing IoT systems' availability as services worldwide. An IoT system can be described as a network of interconnected smart devices and objects that are able to communicate and transfer data using unique identifiers. Communications are processed without the intervention of humans or other computers. IoT has been a platform for different domains, including business, health, and education, which have generated considerable recent research interest. Furthermore, a distributed trust technology, scalability, security, and privacy, is fundamental to the growth of IoT applications [1]. Therefore, blockchain technology requires these underlying features in order to build a solid transaction process. Blockchain first appeared as a solution for the crypto-currency Bitcoin founded by [PERSON] in 2008 [2] which relies on security features such as digital signatures and distributed consensus mechanisms [3; 4]. Its transaction flows in a peer-to-peer network of nodes by generating a chain of data structure that contains blocks of encrypted data and informationin a chronological order. Blockchains basically form a distributed ledger that provides a data storage service and records secure transactions or transactional events using cryptography. Integrating blockchain with the IoT environment will inherit some of IoT's challenges which prevent the direct deployment of blockchain for IoT. In the following, we will discuss critical issues and challenges behind the integration. The crucial challenge has centered around the use of consensus protocol. [PERSON] et al. [PERSON] et al. (2018) have shown the lack of IoT centric consensus protocol through testing a case scenario of an IoT-based supply chain monitoring system. In addition, [PERSON] et al. [PERSON] et al. (2018) have analyzed some challenges related to the use of consensus protocol specifically in the time required to reach a finality settlement. They claimed that most IoT applications require a time-critical operations which indeed affect the finality settlement. The delay is also influenced by the number of nodes which is a primary step in the selection of consensus protocol either public, private, and permissioned blockchain systems. Additionally, storage and trust are critical issues in IoT devices, and blockchains usually generate massive data as composing transaction blocks. The challenge is that IoT devices are unable to verify the transactions generated by others while sender needs historical data. [PERSON] et al. [PERSON] et al. (2018) have stated that the IoT devices should either trust itself by taking the storage load, or trust remote servers, which impose extra communication overhead and secured communication between the IoT devices and the trusted servers. They also claimed that reducing the storage load is done by dealing with IoT devices as a light node in the blockchain system which only save the block headers. Security and privacy have received significant attention in the studies. [PERSON] et al. [PERSON] et al. (2018) have raised an important concern in ensuring the secure input of sensor data to the blockchain. Security should also be confirmed in communication between the IoT devices and the trusted servers. A survey on privacy protection has been presented by [PERSON] et al. [PERSON] et al. (2018). They classified the privacy attacks into de-anonymization and transaction pattern exposure. These threads could be reduced by considering two privacy requirements: identity and transaction.