Computers and Electronics in Agriculture 178 (2020) 105476 Contents lists available at ScienceDirect Computers and Electronics in Agriculture journal homepage: www.elsevier.com/locate/compag Review Integrating blockchain and the internet of things in precision agriculture: Analysis, opportunities, and challenges T Mohamed Torkya,c, Aboul Ella Hassaneinb,c a Faculty of Computer and Information Systems-Islamic University in Madinah, KSA Higher Institute of Computer Science and Information Systems-Culture & Science City Academy, Egypt b Faculty of Computers and Artificial Intelligence-Cairo University, Egypt c Scientific Research Group in Egypt (SRGE), Egypt ARTICLE INFO ABSTRACT Keywords: Precision agriculture Blockchain technology Internet of things Challenges and solutions Blockchain quickly became an important technology in many applications of precision agriculture discipline. The need to develop smart P2P systems capable of verifying, securing, monitoring, and analyzing agricultural data is leading to thinking about building blockchain-based IoT systems in precision agriculture. Blockchain plays the role of pivotal in replacing the classical methods of storing, sorting and sharing agricultural data into a more reliable, immutable, transparent and decentralized manner. In precision farming, the combination of the Internet of Things and the blockchain will move us from only smart farms only to the internet of smart farms and add more control in supply-chains networks. The result of this combination will lead to more autonomy and intelligence in managing precision agriculture in more efficient and optimized ways. This paper exhibits a comprehensive survey on the importance of integrating both blockchain and IoT in developing smart applica­ tions in precision agriculture. The paper also proposed novel blockchain models that can be used as important solutions for major challenges in IoT-based precision agricultural systems. In addition, the study reviewed and clearly discussed the main functions and strengths of the common blockchain platforms used in managing various sub-sectors in precision agriculture such as crops, livestock grazing, and food supply chain. Finally, the paper discussed some of the security and privacy challenges, and blockchain-open issues that obstacles devel­ oping blockchain-IoT systems in precision agriculture. 1. Introduction There is a growing body of literature that recognizes the importance of utilizing emerging technologies in precision agriculture (Zhang et al., 2002; McBratney et al., 2005; Nikkil et al., 2010). Precision agriculture is a new technology that utilizes Information Technology (IT), satellite technology, Geographical Information System (GIS), and remote sen­ sing for enhancing all functions and services of the agriculture sector (Khanal et al., 2017). Today, precision agriculture started to rely upon Mobile apps (Jagyasi et al., 2013), smart sensors (Sartori and Brunelli, 2016), drones (Puri et al., 2017), cloud computing (Mekala and Viswanathan, 2017), Artificial Intelligence (AI) (Jha et al., 2019), in­ ternet of Things (IoT)Ahmed et al., 2018), and blockchain (Ge et al., 2017). Based on these technologies, it is become possible to process and access real-time data about the conditions of the soil, crops, and weather along with other relevant services such as crops and fruits supply chain, food safety, and animal grazing. Many statistical reports announced that precision agriculture will add more improvement to the global economy based on the use of advanced technology in all agriculture subsectors. According to market research and advisory firm, the global market of precision agriculture will grow at an average rate of 13.7 percent to reach 10.55 billion U.S. dollar by 2025 (Xinhuanet, 2020). In addition, the global precision farming market is evaluated to grow from USD 7.0 billion in 2020 to USD 12.8 billion by 2025, at a Compound Annual Growth Rate (CAGR) of 12.7% (Markets and Markets, 2020). In precision agriculture, forecasting and predictive analytic software systems can use agricultural data to provide farmers with guidance about soil management, crop maturity rotation, optimal planting times, and harvesting times, etc. For example, machine learning technology can be integrated with remote sensing for accurate forecasting of crop production and nitrogen levels estimation in precision agriculture (Chlingaryan et al., 2018; Lee et al., 2010). In addition, historical crop planting maps can be used for developing a machine learning system for predicting annual crop planting (Zhang et al., 2019; Elavarasan et al., 2018). Predicting crop growth in the smart greenhouse using a selflearning model and IoT data is another contribution of machine learning in precision agriculture (Kocian et al., 2020). AgriProduction (Dos Santos et al., 2019) is another system that able to anticipate agricultural problems related to soil humidity, temperature, and leaf growth based on both LoRa IoT technology and the ARIMA prediction model. https://doi.org/10.1016/j.compag.2020.105476 Received 25 November 2019; Received in revised form 29 April 2020; Accepted 1 May 2020 Available online 08 September 2020 0168-1699/ © 2020 Elsevier B.V. All rights reserved. Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Sensor technology and IoT can also mitigate various challenges in precision agriculture (Tzounis et al., 2017). Agricultural monitoring systems can provide surveillance services that maintain the plant growing at an optimal level and early anticipate the conditions that lead to epidemic plant disease outbreak based on wireless sensor networks installed in the planted area (Khattab et al., 2019; Ibrahim et al., 2019). Smart irrigation systems based on IoT and sensor technology is another solution for the shortage of clean water resources that are necessary for a lot of plants kinds as well as achieving optimum water-resource uti­ lization in the precision agriculture (Huong et al., 2018). Building flexible and automated platforms able to cope with soilless needs in full smart greenhouses using moderately saline water is an important issue in precision agriculture that depends on combining IoT with cloud and edge computing for mitigating this challenge. Deep learning technology represents a recent technology in preci­ sion agriculture (Kamilaris and Prenafeta-Bold, 2018). This new tech­ nology can help in designing automated and reliable fruit detection systems for fruit yield estimation and automated harvesting through applying neural network models on imagery data obtained from two modalities: color (RGB) and Near-Infrared (NIR)Sa et al., 2016) like Mango fruit detection (Koirala et al., 2019), cotton detection and seg­ mentation (Li et al., 2017), and apple detection and segmentation (Kang and Chen, 2019). Utilizing deep learning for visual detection and re­ cognition of weeds in grasslands is an additional contribution of deep learning in terms of weed control in precision agriculture discipline (Kounalakis et al., 2018). Decision Support Systems, data analysis, and data mining become a significant technique for managing many services in precision agri­ culture (Zhai et al., 2020). Managing smart farms through web-based decision support systems can help in complying with many require­ ments in precision agriculture such as crop production, optimizing farming costs, and monitoring market dynamics in more efficiency (Narra et al., 2020). In addition, many steps have been made to improve irrigation decisions based on various irrigation decision models that can help the farmers to carry out critical irrigation actions and optimize irrigation depth (Car, 2018; El Baki et al., 2018). Moreover, water loses reduction and improving water supply efficiency can be achieved through automating irrigation canal operations, and manipulating both known and unknown patterns of water demands that can be recognized by different irrigation systems in the farms (Shahdany et al., 2019). Agricultural robotics has brought also a significant development for various applications in precision agriculture (Pedersen et al., 2006). The objective of agricultural robotics is more than just the use of ro­ botics for specific functions in precision agriculture, but most of the recent the automatic agricultural vehicles are multi-function, such that it can be used for weed detection, agrochemical dispersal, terrain le­ veling, irrigation, field supervision, as well as tree fruit production (Cheein and Carelli, 2013; Bergerman et al., 2015). Moreover, devel­ oping a smart drone system becomes an interesting and significant technology in precision agriculture (Mogili and Deepak, 2018). Smart drones able to solve many big challenges in precision agriculture such as irrigation monitoring, weed identification, crop dusting, crop mon­ itoring, pesticide spraying as well as deterring fertility levels, identi­ fying bacteria, fungus or diseases based on Infra-red radiation com­ monly reflected from sensors or thermal imagery (Smith, 2020). Recently, blockchain represents the last new technology that can be used for mitigating significant challenges in precision agriculture, especially when integrated with IoT technology (Tripoli and Schmidhuber, 2018). According to a new market intelligence report by BIS Research, employing blockchain technology in precision agricul­ ture,and food supply chain markets is anticipated to increase from $41.9 M in 2018 to $1.4B by 2028 (BIS Research, 2018). Blockchain can introduce a variety of benefits and support in several applications in precision agriculture. For instance, Smart farming, supply chain mon­ itoring and tracking (Lin et al., 2018; Bordel et al., 2018; Tse et al., 2017; Casado-Vara et al., 2018), finance management (Chinaka, 2016), data assurance and security (Mann et al., 2018; Xie et al., 2017; Liang et al., 2017). The Increased utilization of the public blockchain in food markets has also motivated the governments to restructure their legis­ lative frameworks and regulations to consider blockchain in its eco­ nomic policies. Recently, the need for blockchain in precision agri­ culture is mandatory to bridge the demand and supply gap along with attaining sustainability in the ecosystem. Although some reviews studies in integrating blockchain with IoT have been introduced (Dorri et al., 2017; Fernáez-Caramés and FragaLamas, 2018), these reviews didn’t go deep into investigating the benefits and solutions that blockchain can introduce for developing new applications in precision agriculture (Bermeo-Almeida et al., 2018). As a response to this limitation in the literature, this paper is one of the first mature studies that introduces a holistic approach and a systematic review for investigating more contributions of blockchain technology in precision agriculture. The rest of this paper is designed as follows: Section 2 introduces an overview of blockchain technology. Section 3 discusses the major contributions of Blockchain in IoT applications. Section 4 discusses the major uses cases of integrating blockchain with IoT in precision agriculture. Section 5 discusses some challenges and open problems that obstacle building blockchain-IoT networks in pre­ cision agriculture. Finally, Section 6 summarizes the general conclu­ sion. 2. Blockchain technology: an overview The theory of Blockchain was invented by ”Satoshi Nakamoto” in 2008 to work as a public ledger of the bitcoin transactions (Nakamoto, 2008; Al-Jaroodi and Mohamed, 2019). The concept of blockchain can be defined as a decentralized, distributed ledger for storing timestamped transactions between many computers in a peer to peer net­ work. So that any involved record cannot tamper retroactively. This allows the blockchain users to audit and verify transactions in­ dependently and transparently. So, the blockchain can be designed as a growing stack of records, called ”blocks”, which are connected using cryptographic techniques. Each block must have a hash code of the previous block, a timestamp, and a set of confirmed transactions (Zheng et al., 2017). Simply, a blockchain is an invented way to structure data in a decentralized manner, which structured as a book that contains an infinite number of pages, each page (i.e. block) contains new transac­ tions in the blockchain. The blockchain ledger is controlled autono­ mously using a P2P network and a public time-stamping server (Tapscott and Tapscott, 2016). The decentralized transparent design of blockchain tracing and secure the transaction workflow. This feature can solve the long-standing problem of double-spending (Chohan, 2017). In the blockchain, each block has a unique hash value that identifies the identity of the block. The first block in the chain is named a ”genesis block” which has no parent block as depicted in Fig. 1. The general architecture of each block is explained in Fig. 2. Each block unit consists of a block header and a block body. Especially, the block header involves six components: • Block version is a software version number indicates which con­ sensus protocol to follow. • Markle Tree Root Hash is used to verify the hash code that iden­ • • • • 2 tifies all block transactions.It recursively defined as a binary tree of hash codes. Timestamp is given in seconds since 1/1/1970. It is used to im­ mutably track the creation and update time of the block for block integrity guarantee. N-Bits identifies the target threshold of hash code that specifies the valid block. Nonce is an arbitrary number that can be used just once in a cryptographic communication. It is a 4 byte field, which usually begins with ’0s’ and grows for every hash computation. Parent Block Hash is a 256 bit hash code that refers to the Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 1. Blockchain as a sequence of hashed blocks. previous block. Without this component, there would be no con­ nection and chronology between blocks in the blockchain. 2.1. Blockchain features Blockchain has four major features as depicted in Fig. 4 that make it is better than the common centralized database systems: On the other hand, the block body contains all the number of transactions that are confirmed and validated within the block. All transactions in the block are counted via Block Transaction Counter (BTC). The block state represents who sent which data (e.g. Bitcoin) to whom at a specific timestamp. An identified transaction between two nodes only occurs once it is involved in a block, then the block is ver­ ified and added to the blockchain. To achieve this, the ledger must be publicly available, this clears the importance of peer-to-peer networks in blockchain systems (Zyskind and Nathan, 2015). Fig. 3 explains how the blockchain system works while a user ’A’ transfers a transactional data (e.g. bitcoin) to a user ’B’. In a P2P network, the nodes can guar­ antee the blockchain is protected and up-to-date, where, every node stores the last updated version of the blockchain. Utilizing P2P network architecture in the blockchain system has three main advantages: • Decentralization: The set of transactions in blockchain are pro­ • • 1. The user can always brows and check the blockchain status by a blockchain explorer without depending on a third party 2. A malicious attacker is challenged to attack thousands or millions of nodes at the same time in order to compromise the blocks 3. Blockchain is never removed because it would have to be re­ moved by all nodes in P2P network • cessed and validated through a distributed ledger-based on P2P network. For example, in the bitcoin blockchain, there is no need for the central trusted party (i.e. the central Bank). All nodes work to­ gether as peer to peer for adding and verifying block transactions in the blockchain. Persistency: In blockchain, it is impossible to drop or rollback an identified transaction once it is added to an block in the blockchain. Moreover,invalid transactions could be discovered immediately. Anonymity: Each participant can communicate with the blockchain by a generated virtual identity code, which does not uncover the real identity of the participant. Hence, this feature raises several security and privacy challenges of blockchain transactions (Kosba et al., 2016). Auditability: This feature specifies that each block is securely linked to the previous block. This design makes transactions are easily verified and tracked. With respect to who are the miners and validators of blocks in blockchain, who is authenticated to access blockchain system, level of Fig. 2. Block design. 3 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 3. Blockchain system working. network. These principles make sure the blockchain system works as intended to do in a synchronization manner. The blockchain protocol sets rules on three key issues: creating data blocks, verifying and vali­ dating data blocks, as well as resolving block conflicts in the chain. Recently, there are different blockchain protocols used to verify and add blocks to the blockchain in different ways. A newly mined block can be inserted to the blockchain if it follows the formulated principles stated by the blockchain protocol. Then, the peers in the network run software to test if the block is rightful or not. An illegal block will simply be rejected. In Table 2, the functionality of some major con­ sensus blockchain mechanisms is presented and compared in terms of the mining process, the used technology for generating blocks, the power save during mining process,the block verification speed, the network structure on which each protocol is working, scalability, access rights to users, and a platform example for each protocol. As depicted in tale 2, the main disadvantages of old protocols such as Proof of Work (Pow) (Zheng et al., 2018), Proof of Stake (PoS) (King and Nadal, 2012), Proof of Authority (PoA) (Bentov et al., 2014; Lin and Liao, 2017), and Proof of Burn (PoB) (Frankenfield, 2018; CoinCheckup, 2019) are that those protocols consume more powers and have low speed during mining process. On the other side, the new protocols such as Proof of Luck (Pol) (Milutinovic et al., 2016; Kim et al., 2015; Chen et al., 2017), and Proof of Assignment (PoAss) (ICO Bench, 2019; IOTW, 2019) are more power savers and able to generate a new block in the blockchain in less than 10 s. Moreover, these protocols is working based on novel secure technologies, such as Intel Software Guard Extension (SGX) as in Pol (Milutinovic et al., 2016; Kim et al., 2015; Chen et al., 2017), and green mining technology as in PoAss (ICO Bench, 2019; IOTW, 2019). This novel technologies provides more security, trusted environments for block mining, and more power saving during block verification and generation. The literature introduced additional blockchain protocols that can be used in different fields and applications, for instance, in crypto­ currency exchange (Schwartz et al., 2014; Buchman, 2016; Bach et al., 2018; Gibbs and Yordchim, 2014; Jake Frankenfield, 2019; Chohan, 2019; Mser et al., 2018; Hileman and Rauchs, 2017; Chang and Svetinovic, 2016), identity verification and privacy preserving (Umeh, 2016; Jeffrey Maxim, 2019; Keybase, 2019; Eric Weiss, 2019), E-gov­ ernment sector (Aman Soni, 2018; Nuss et al., 2018; Buchmann et al., 2017; Vos et al., 2017; Pawlak et al., 2018), healthcare systems (Brennan, 2017; Azaria et al., 2016), and energy and smart grids (Martens et al., 2017; Pop et al., 2018). Fig. 4. The major features of blockchain. Table 1 A Comparison between blockchain types. Property Public Blockchain Private Blockchain Consortium Blockchain Blockchain Validation Access Rights Immutability and Security Efficiency Centralization Blockchain Authority All peers One organization public or Private tampered Selected peers public or Private tampered High Yes Permissioned High Partial Permissioned Public Very tough to tamper Low No Permissionless security and efficiency, design method, blockchain authority, block­ chain systems can be classified into three types: public, private, and consortium blockchain which are compared in Table 1. 2.2. Blockchain protocols Executing a specific blockchain protocol is where the magic occurs. It allows all nodes in a P2P network to cooperate and work together without trust requirements between them. The blockchain protocol is responsible for verifying and securely adding blocks to the chain ac­ cording to the set of mining rules. So, the blockchain protocol is simply a set of principles that are agreed upon by all peer nods in the P2P 4 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Table 2 A comparison between six blockchain protocols. Measure Pow (Zheng et al., 2018) PoS (King and Nadal, 2012) PoA (Bentov et al., 2014; Lin and Liao, 2017) PoB (Frankenfield, 2018; CoinCheckup, 2019) Pol (Milutinovic et al., 2016; Kim et al., 2015; Chen et al., 2017) PoAss (ICO Bench, 2019; IOTW, 2019) Mining Base Tech. Handling Power Save Verification Structure Scalability Access Platform puzzle coin-based No No > 100s P2P high public Bitcoin-NG (Eyal et al., 2016) wager coin-based partial partial < 100s P2P high public Peercoin (King and Nadal, 2012) puzzle + wager coin-based partial No < 100s P2P high public Coin Proz (ProzCoin, 2019) burn coins. coin-based No yes < 100s P2P high public Slimcoin (CoinCheckup, 2019) luck algo. Intel SGX yes yes < 10s P2P/central high public/private Hayekcoin(ANN, 2019) hashcodes green mining yes yes < 10s central low private IOTW (IOTW, 2019) 3. An integration model between blockchain and IoT energy and smart grids (Yang et al., 2017) is another important trend by 2030. In the subsections below, we will discuss in more details the blockchain design patterns for IoT, the major solutions which block­ chain can provide to IoT challenges, as well as the recent blockchain protocols in IoT. Internet of Things (IoT) is a base technology and key player in the digital transformation witnessed by industry 4.0 (Lu, 2017). In industry 5.0 (Daniel Sontag, 2019), IoT is predicted to have more dependence on sensing devices, big volumes of data, and more patterns of connected devices within different network topologies. we must call it the Internet of Things 2.0 (Sheth, 2016). Recently, IoT 2.0 moves from devices and data technology to Actionable Intelligence Technology (I-Scope, 2019). Based on more integration between IoT as a base technology and other technologies such as AI, Cloud Computing, and Data Science, the digital transformation moves from IoT 2.0 to the Internet of Transformation which makes the IoT communications so powerful (I-Scope, 2019; Darwish et al., 2017; Vermesan et al., 2017; Sowe et al., 2014). The integration of blockchain technology with IoT is another im­ portant contribution predicted to revolutionize the digital transforma­ tion of various domains (Makhdoom et al., 2018). Blockchain as a distributed ledger can be verified and deployed across several hetero­ geneous IoT networks. In IoT-based environments, Blockchain is pre­ dicted to add 176B$ to the global economic value by 2025 and over 3T$ by 2030 (Fourquadrant, 2019). Fig. 5 explains the top five predictions of integrating Blockchain with IoT by 2030. For example, In e-governments, by 2030, most governments will depend on digital currency in most of (maybe all of) financial transactions. In the digital economy, by 2030, blockchain will produce more token-based protocols for enhancing digital economy transactions. By 2030, the Self-Sovereign Identity standard (Baars, 2016) will emerge for managing the individuals’identities locally and internationally. One of the most promising trends where blockchain and IoT can work together by 2030 is the global supply chain man­ agement and tracking. Moreover,Blockchain and IoT benefits in digital 3.1. Blockchain design patterns-based IoT Networks In IoT-device communications, IoT peers collaborate and build trust over a blockchain design pattern. Each IoT- peer device can be re­ presented by one or more nodes in a P2P network. This network is used to broadcast IoT transactions between devices based on a blockchain protocol. This protocol is responsible for managing, verifying, and se­ curing IoT transactions. The Effective monitoring and management of a blockchain-IoT network system requires a special framework for managing data traffics, and sense the events and transactions between IoT devices. The blockchain-IoT framework should be modular enough to enable the monitoring of a variety of IoT transaction Patterns as discussed in (Hitarshi, 2019). Fig. 6 depicts a proposed update of the Standard Blockchain Monitoring Framework in IoT (SBMF-IoT) when utilized to monitor three trucks which provide food patterns to various customers through a specific food production company. The SMBF-IoT comprises of the following components: 1. A Monitoring Agent (MA) which embedded with each IoT truck through the associated IoT-decentralized Application (IoT-dApp). It can read the logs generated as a part of the transaction process. 2. A log Collection Engine (LCE) that manipulates the streaming log information of IoT trucks and realize it for further transaction pro­ cessing. 3. The Elastic Nodes Cluster (ENC) which processes a large amount of log data to organize and index it into matching IoT data files, which are shared and stored as replicas. 4. A Visualization Platform (VP) consumes the transactional IoT data collated by ENC and provides effective insight into the block­ chain nodes and network statistics. Leveraging the SBMF-IoT as a design standard for managing and monitoring blockchain-IoT transactions will help in achieving the fol­ lowing: • Providing transparent end to end IoT transactions. • Providing more control in the performance and throughput of the blockchain network. • Installing non-invasive monitoring routines that can be dynamically enabled for each on-boarded IoT peer and also support a common network provider model. The blockchain is a distributed ledger that will perform a major role in how IoT-devices will be linked together directly/indirectly between each other. Integrating blockchain within IoT communications require Fig. 5. Top five predictions of integrating blockchain and IoT by 2030. 5 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 6. Standard Blockchain Monitoring Framework in IoT (SBMF-IoT): A proposed Model. to identify the design pattern on which the communication occurs: the communication may be in three basic design patterns: from IoT device to IoT device, from IoT device to the blockchain, or a hybrid design. The key benefits of utilizing blockchain as a design base for IoT transactions are building trust, reducing cost, and accelerating transactions. -IoT to IoT Design Pattern: In this design pattern, blockchain work as only data storage for IoT- devices. Only some bytes of data are re­ gistered in the blockchain whereas the IoT communications occur outside the blockchain. This design would be helpful in scenarios where the IoT interactions are taking place with low latency. Fig. 7 explains how two IoT-cars are communicating based on IoT-IoT design pattern via a Management Hub component which allows the IoT devices to store data in the blockchain. -IoT to Blockchain Design Pattern: In this design pattern, all IoT interactions go through blockchain. It works as a data storage and transaction monitor and manager. This design guarantees that all IoT communications are traceable as defined in the blockchain. Moreover, it increases the independence of IoT nodes such that each device can interact directly with the blockchain. This design approach is effective when the transactions happen between a variety of IoT devices in dif­ ferent domains. However, assimilating a large number of IoT transac­ tions and data volumes in blockchain will lead to bandwidth and la­ tency problems. So the scalability is one of the well-known dilemmas of blockchain (Tasca and Widmann, 2017). Fig. 8 explains the three types of interactions between three IoT-devices with the blockchain, IoTbuilding,IoT-energy node, and IoT-Truck. Although the three nodes Fig. 8. Multi IoT-devices to Blockchain-design pattern: A proposed model. appear that they are heterogeneous, based on this design pattern, the blockchain is used as a storage repository for heterogeneous data as well as a transaction monitor, and a verifier for different communica­ tion patterns. -Hybrid Design Pattern: In the early years of IoT communications, the disparate endpoints of IoT-devices were not doing a lot of data analysis and processing. Now, the endpoints are talking to each other with more interdependence and processing more data, this a promising approach is called Edge Computing (Satyanarayanan, 2017). The in­ tegration between IoT and other technologies, including Fog Com­ puting (Chiang and Zhang, 2016), Artificial Intelligence (AI) (Vermesan et al., 2017), and blockchain (Li et al., 2018) leads to a hybrid design pattern. In this pattern, the data needs to be manipulated just on the IoT-device and does not need to be transmitted back to the cloud. Also, AI will become a key player in this design pattern. such that it will help IoT devices to make critical decisions. Blockchain can be leveraged for providing trust and security as missed links in the edge computing approach. The hybrid IoT network requires more security and relia­ bility. Moreover, it requires a lot of transmitted data volumes and dif­ ferent IoT transaction patterns which can be managed by the Block­ chain. Fog Computing can play a major role in this design pattern. It can remedy the limitations of blockchain and IoT regarding energy con­ sumption and computing power, such that fog computing-based devices such as gateways, and data sensors require a little computation power. These advantages make fog computing a key player for reducing the Fig. 7. IoT- device to IoT- device- design pattern: A proposed model. 6 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 9. Hybrid design pattern: A proposed model. amount of bandwidth and latency. Moreover, it accelerate blockchain mining operations. Fig. 9 explains the architecture of the hybrid design pattern which integrates IoT, Cloud Computing, Fog Computing, and Blockchain in a coherent design model. This figure depicts how blockchain can be utilized to work as a data repository and transactions monitor and verifier for two different heterogeneous fog networks that are managed by a cloud. The strength of this design pattern here is that blockchain is not only dedicated to store and verify data from different IoT devices as explained in the previous design pattern but also to store and verify data from different heterogeneous and complex fog and cloud networks. the other side, Precision agriculture network systems are challenged by network performance problems such as the communication speed with a huge number of heterogeneous devices and sensors, the power con­ sumption of these devices, bandwidth and latency as well as limited data storage. So, this section explains how blockchain technology can makes IoT communications are more secure, transparent and tamper­ proof. Moreover, it will improve digital agricultural processes with realtime data monitoring in accelerated end-to-end transaction processes. Hence, blockchain technology can introduce good solutions to the se­ curity and performance of IoT networks in the precision agriculture systems. 3.2. Challenges of IoT networks and blockchain solutions 3.2.1. IoT security challenges and blockchain solutions By 2025, it is predicted that will be more than 21 billion IoT nodes (more than 75 million IoT devices in agriculture sector lonely) which will motivate the attackers for executing a variety of IoT attack patterns (Norton, 2019). In 2016, Mirai malware (Kambourakis et al., 2017) has been considered as the first IoT malware that can infect linked devices such as Digital Video Recorder (DVR), IP cameras, and home router. This malware is able to turn the affected devices into a botnet for ex­ ecuting Denial of Service (DDoS) attacks (Kolias et al., 2017). Another example is IoT-reaper (Gary Davis, 2019), which appeared in 2017. It Building robust IoT networks in the precision agriculture systems is challenged by a lot of network security threats, and communication performance dilemmas in this type of networks (Makhdoom et al., 2018). For example, farmers need to secure supply chain systems for trading their crops and protecting their smart greenhouse networks against cyber attacks. Moreover, they need a trusted environment to manage and access their IoT-agricultural machines without threats to identity, privacy, and integrity of data processed by those devices. On 7 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Signature Algorithm (ECDSA) is 20 bytes (Ziegler et al., 2015). With 160-bit address space, blockchain can derive and assign addresses spaces about 1.46 * 10 48 for IoT nodes (Khan and Salah, 2018). Hence, the possibility of address collision is roughly 10 48 , which is secure enough to assign a GUID (Global Unique Identifier) to IoT devices. With blockchain technology, there is no need for a central authority for providing and generating limited Internet Assigned Number Authority (IANA) (Ziegler et al., 2015). Furthermore, blockchain able to derives 4.3 billion addresses spaces compared to IPv6. So, Blockchain provided a magical solution for solving the scalability and security challenges in IoT. 2) Managing Identity of Things. Generating identities and mana­ ging access for IoT devices is considered another benefit of blockchain in IoT security. Blockchain can be utilized for granting trustworthy identity creation, ownership monitoring and tracking of goods, pro­ ducts, and services. Data transparency and end-to-end process tracking is another benefit of robust blockchain. For example, Trust-Chain (XXXX, YYYY) has been proposed for verifying and managing trusted transactions while maintaining the integrity in distributed IoT net­ works. Each Block in the Trust-Chain represents a transaction between two IoT participants and creating new transactions is depending on the hash codes of the previous transaction. Trust-Chain records are cryp­ tographically authenticated and signed by both parties and connected in a directed graph. The main advantage of Trust-Chain beside security is each agent in the Trust-Chain system monitors the interactions by others and collects records to compute trustworthiness levels. Block­ chain also can provide control functions for trustworthy and decen­ tralized transactions in the three design patterns explained previously. Moreover, it allows to remote asset management and instant data ver­ ification from end to end between IoT devices. 3) IoT Transaction Verification: Blockchain can perform an important function in managing the authentication and authorization of IoT systems. With blockchain, all IoT transactions mad by devices are registered on the distributed ledger and can be monitored and tracked securely. Each IoT transaction communicated with the blockchain system will always be crypto­ graphically proofed by the valid sender that holds a unique PK and GUID. Hence, this will be helpful in ensuring the authentication and integrity of the triggered transaction. Blockstack (Ourad et al., 2018) is a common blockchain technique that utilizes JSON Web Token (JWT) for authenticating IoT-transactions easily. As depicted in the proposed model in Fig. 11, Blockstack can be used to authenticate the access to a smart greenhouse. The authentication with Blockstack requires a spe­ cial communication between a decentralized application (DApp) of an IoT greenhouse and the Blockstack Browser. The authentication process can be explained through eight steps: doesn’t intrinsic depend on breaking prosaic passwords like Mirai does, but instead avails the vulnerabilities in various IoT devices and exclude them into a botnet cram. Due to the limitation to unstandardized se­ curity models for IoT, Other attacks can execute data forgery routines, data block and encryption. Ransomware (Yaqoob et al., 2017) encrypt victim’s data and ask for a ransom to decrypt it can work in different ways with IoT devices. It needs to identify the correct IoT-device owners to ask for ransom money. Moreover, plenty of IoT devices are operated by other devices; hence, the attacker needs to get the In­ dustrial Control Systems (ICS) to penetrate the target device and en­ crypt the data. Shamoon 2 and DuQu-2 (Makhdoom et al., 2018) are another IoT attack models that target ICS of IoT devices based on its ability to replicate across different operating systems and IoT devices. In 2012, King Saudi Arabia announced that there were about 15 gov­ ernmental proxies and communities have been attacked with Shamoon 2 (Smith, 2019). Shamoon removed data within 35,000 devices and hijacked the computer’s boot record, which prevents the computer from being rebooted. Hence, the development of future IoT communication systems requires to meet the following security requirements: 1. IoT devices have to operate securely in an authenticated manner. 2. Data integrity should be ensured versus data forgery, alteration and unauthorized access. 3. The IoT-device codes have to be secure against Tamper proof. 4. All IoT-devices have to be authenticated within the IoT system before installed in the network. 5. IoT Networks have to be tamper-resistant regarding both software and hardware tamper. 6. IoT data should be encrypted with efficient and secure key gen­ erator systems in which the breaked key can be updated as and when required 7. IoT systems have to ensure user security such as, ID management, enrollment, authentication, authorization, and non repudiation. 8. IoT system has to be immunized against unauthorized access to private IoT data and network. By the coming generations of blockchain systems and the advance in developing untraditional smart contracts and distributed ledger, it is expected that blockchain will provide magic solutions for many chal­ lenges in IoT networks security and achieve the required security re­ quirements. Fig. 10 depicts the key solutions, which blockchain can grant for IoT-networks security (Khan and Salah, 2018). In the fol­ lowing, these key solutions of blockchain that can mitigate the security challenge in IoT networks are discussed in some details. 1) Extending Address Space: The limitation of IPv6 address space is a big scalability challenge for addressing IoT devices. IPv6 has a 128bit address space, whereas Blockchain has a 160-bit address space. So, with blockchain addressing, the generated PK by Elliptic Curve Digital 1. A user (e.g. farmer) signs in with blockstack by requesting a new access to the smart greenhouse by establishing a new connection with its decentralized application (DApp). 2. The DApp then sends the sign in data to the function ”Redirect _To _Sign ()” for processing the access request. 3. The function ”Redirect _To _Sign () ” asks the blockstack browser to generate a new Authentication Request Token for the user’s access re­ quest. 4. The blockstack browser responds bycreating new JWT authentica­ tion response token that being forwarded to the DApp. 5. The DApp then manipulates the JWT authentication response token by calling the function Habndle _Pending _Sign () for verifying the issued JWT authentication response token by the blockstack browser. 6. After the function Habndle _Pending _Sign () has verified the JWT token, it forwards the JWT verification result to the DApp for re­ sponding the user’s access request. 7. The DAppm then grants the user the required access data to access greenhouse system. Fig. 10. Key security solutions of Blockchain for IoT. 8 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 11. Blockstack authentication protocol: A proposed model. different bandwidth options. 2. IoT platform layer:It is sometimes called network layer. It defines the various communication protocols and networks used for con­ nectivity and edge computing. So, it is responsible for recording and analyzing the transmitted data from sensors and other physical endpoints through session protocols between IoT gateways and IoT platform. 3. Application Layer. Is responsible for providing IoT services to the end users through several applications such as mobile applications, public web or back-office applications. It depend on HTTP protocol to exchange data between the IoT platform and those applications. 8. The user (e.g. farmer) inputs the granted access data and establishes the connection with his greenhouse system. 4) Securing IoT Communications: To provide secure communication between IoT devices, the classical protocols such as ”Hypertext Transfer Protocol (HTTP)”, or ”Extensible Messaging and Presence Protocol (XMPP)” must be replaced with more secure protocols such as ”Datagram Transport Layer Security (DTLS)” or ”Transport Layer Security (TLS)” for providing secure communica­ tion (Nguyen et al., 2015; Kothmayr et al., 2013). However, DTLS or TLS protocols have some drawbacks in terms of computation time or memory requirements as they considered heavy and complex protocols. Moreover, these protocols have some problems with centralized gov­ ernance and control of key generation and distributions using the common PKI protocol. Using blockchain can remove these problems and enhance key management between IoT devices by assigning each device a unique GUID and PKI pair once installed and connected to the blockchain network (Khan and Salah, 2018). With blockchain, new secure communication enhancement can be conceived such that there is no need to handshake phase to exchange PKI certificates as in DTLS or TLS protocols. Therefore, blockchain is the best solution to cover run­ time computing and memory management requirements for achieving secure communications between IoT devices. Moreover, the firmware of the IoT devices can be hashed into a Blockchain continually for de­ tecting IoT Malware and alert the device owners to take the necessary security measures, or auto defends against the detected malicious bot. Instruction verification and authentication is another benefit of block­ chain for securing communication between IoT devices. For instance, the sender node hashes a message that wants to forward to another IoT node and add the hash code into a Blockchain. On the other hand, the receiver node then hashes the same message. The verification rule state that, if the hash value matches the hash value on the Blockchain, then the received message has not tampered in the transit. The IoT performance problems in the precision agriculture networks can be summarized in five challenges as depicted in Fig. 12. Blockchain can provides also good solutions for the those challenges: (1) Blockchain and Sensing problem. This problem is concerned with the perception layer in IoT layer model. IoT sensors are embedded in a lot of agricultural machines, such as agriculture tractors,smart greenhouses, farming devices, etc. These sensors continuously emit data about the working status and permit IoT nodes to send and receive data from each other via the cloud. Blockchain can be used for defining communication rules between these sensors as well as managing all M2M transactions. For instance, IOTA (Internet of Things Application) (Popov, 2016) is a promising update of the blockchain platforms which specially designed to facilitate a large number of transactions between IoT devices using IOTA ledger and Directed Acyclic Graph (DAG). Al­ though IOTA is still new, it can provide magic solutions for the sensor 3.2.2. IoT performance challenges and blockchain solutions Due to the huge number connected IoT devices in the precision agriculture networks, IoT system have to harmonize a future large number of network topologies and process big data volumes with high level of throughput. So, the performance of IoT networks in the preci­ sion agriculture systems represents another big challenge. The IoT performance problems result from some limitations in the traditional IoT layer model that involves three basic layers. The endpoints and gateway layer, The IoT platform layer, and the Application layer. 1. Endpoints and Gateway layer: It is sometimes called perception layer that involves several IoT devices such as sensors, controllers, and mobile devices. in this layer, the physical endpoints send IoT messages to the IoT platform through a gateway. Each sensor con­ nects to the gateway through one of several data link protocols with Fig. 12. IoT performance challenges in the precision agriculture networks. 9 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein communications and the scalability challenge in the precision agri­ culture. (2) Blockchain and Energy Consumption Problem: This problem is concerned with the Network layer in IoT layer model. Due to the increasing of IoT network systems in the precision agriculture, IoT devices are predicted to be low-power devices. Moreover, IoT com­ munications in precision agriculture networks are depending on Wireless technology which consumes far more energy than wired con­ nections Such as Fiber (5G? IoT, 2019). Although fiber is safer, faster, more reliable, and energy-efficient than wireless, pushing for 5G tech­ nology everywhere is cheaper than to depend on fiber. But un­ fortunately, this will greatly grow energy consumption. Recent IoT devices in precision agriculture networks consume energy via data centers, M2M communication, embodied energy (e.g. mining, manu­ facturing, and transporting), and Obsolescence of digital technologies. But with the decentralization feature of Blockchain, it can introduce some solutions to handle the energy consumption problem. The private blockchain can be utilized for ensuring the proportion between the high computation power along with the high bandwidth connection for IoT nodes (Makhdoom et al., 2018). Blockchain will grant the resilience needed for the smart grids in the future. Blockchain-based flexible power systems will witness low-carbon power produced at scale-not only by large utilities, but also by renewable power sources. Blockchain will enable us to measure how much energy IoT-devices and sensors consume in real-time. Blockchain can maximize three energy trends decarbonization, digitization, and electrification (Maher Chebbo, 2019). All renewable energy-based processes such as energy selling/ payments transaction, and energy contracts can take place on a blockchain immediately. Blockchain can provide techniques for col­ lecting and storing data from countless distributed sources as well as processing it in real-time. Blockchain will also maximize the elec­ trification by providing decentralized energy ledgers for monitoring a large number of batteries and a variety of energy sensors used in the precision agriculture networks. (3) Blockchain and Networks Complexity Problem: This problem is also concerned with the Network layer in IoT layer model. IoT sys­ tems in precision agriculture are designed based on un heterogonous Network topologies which lead to complex communications. The IoTfarming machines have to communicate and interact seamlessly through different platforms and infrastructures. It’s possible, but it can be hard, expensive,and time-consuming. In response to these chal­ lenges, Blockchain can help in acquiring and managing data based on secure standard-based and decentralized networks. As we mentioned previously in Section 3.1, blockchain can manage the communications between IoT devices through three design patterns, this lead to more simplicity in IoT communications, supporting edge processing at farming machines endpoints, and decrease the latency of data trans­ mission across the precision agriculture networks. (4) Blockchain and bandwidth and latency Problem: Another important IoT performance problem against building precision agri­ culture networks is the bandwidth and latency of device communica­ tions. In IoT communications, the data traffic always originates outside the data centers. Hence, immediately, the communication has to be installed in the highest latency between large numbers of scattered IoT devices. A large number of different IoT devices need to be updated every small time period. Moreover, device communication needs lots of routing and multiple levels of packet inspection. Replacing the data center with blockchain will mitigate these problems. The decen­ tralization feature of blockchain will make the workload more dis­ tributed closer to the endpoints. Hence, the IoT communication will be constructed inefficient bandwidth and low latency. However, the de­ centralized public blockchain may take control of the public nodes is very difficult such that there is a great chance that the IoT device with the smallest bandwidth will cause network bottleneck. In addition, due to the growth of blockchain size, the need for computing power, Table 3 Cloud versus Blockchain as a data storage medium. Cloud-based Storage Blockchain-based Storage Centralized Trust by the cloud provider Centralized Design Not protected against data alteration Single point of failure Vulnerable to un-authorized data propagation User data is managed by Decentralized Trust in the network Decentralized Design Protected against data alteration multi points of failure data propagation are based on smart contracts User data is replicated between all peers and controlled by smart contracts. The transactions are transparent to user identities. Provide edge/fog computing at IoT endpoints so it is a good option for IoT networks. Less expensive infrastructure cloud provider The transactions aren’t transparent regarding users identities Not ideal for low latency and high availability for IoT networks Costly design infrastructure storage,and bandwidth is very importantMakhdoom et al., 2018). On the other hand, with a private blockchain, these limitations can be re­ moved, such that the private Blockchain can process over 1,000 transactions per second on Ethereum or Bitcoin (Preethi, 2017). Hence, a huge number of heterogeneous agriculture transactions can be pro­ cessed using the coming blockchain systems based on processing digital asset tokens. (5) Blockchain and Limited Data Storage Problem: Due to the rapid growth of IoT-precision agriculture networks, large volumes of data have to be stored and managed through flexible repositories. The existing cloud-based storage has limited solutions to manipulate the large scale of different patterns of IoT data. This limitation based on the requirements of real-time data monitoring, high availability, scalability, security, and low latency (Sharma et al., 2017 Sep). In response to these limitations of cloud-based storage, Blockchain-based storage will enable IoT endpoints to make more data analysis and manipulation in realtime. Satyanarayanan (2017). Table 3 explains the major differences between cloud-based storage and blockchain-based storage. The P2P design of blockchain makes the trust is replicated among all peers. Hence, if any tamper occurred in any node, all peers in the system will detect it rejects its procedure, moreover, the current status of block­ chain will not be modified or tampered. Moreover, the cloud is also vulnerable to unauthorized data sharing, whereas, blockchain gives users the freedom to set access rules without dependence on a third party or a cloud service provider. Hence, blockchain is also a very good option for data availability and security (Makhdoom et al., 2018). 4. Blockchain opportunities in IoT-based precision agriculture The IoT growth in the last few years has granted many opportunities for enhancing the precision agriculture sector. The witnessed increase in using mobile-broadband access devices, smart networks, analyzing big data volumes, and AI have provided the stakeholders with some magic tools in developing precision agriculture systems. Blockchain is one of the most promising technologies that can provide untraditional solutions in smart agriculture (Lin et al., 2017). Blockchain can be used in managing warehouses, soils, and supply chains more intelligently. It can be utilized as a key tool to transmit real-time data about crops and livestock. Moreover, it can be used for food safety, logistics, monitoring, as well as managing payment transactions (Sam, 2018). Blockchain adoption in smart agriculture and food supply chain market is predicted to grow at a CAGR of 47.8% by 2023 (Report Linker, 2018). Moreover, utilizing blockchain in the supply chain market is evaluated to be $60.8 million in 2018 and is forecasted to reach $ 429.7 million by 2023 (Report Linker, 2018). In the following subsections, the major use cases of utilizing blockchain in developing IoT-precision agriculture networks 10 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein proving quality and ethicality (Caro et al., 2018). This can provide consumers and stakeholders more trust in the agricultural products, ensuring food safety, and reducing food frauds (Sylvester, 2019). In the supply chain process, blockchain can provide key five services: 1. Data Recording. Blockchain is able to work as a distributed storage unit for all information moving between supply chain nodes 2. Monitoring. Blockchain is able to track purchases, orders, updates, receipts, shipment notifications, or other trade-related transactions (Li and Wang, 2018). 3. Verifying. Blockchain can be utilized for verifying transactions or certain properties of physical products, such as identifying if a food product is an organic or fair trade (Platform with duplicated and shared bookkeeping, 2018). 4. Assigning and Linking. Blockchain can be used to link the physical products to bar codes, serial codes, digital tags like RFID, etc. 5. Sharing. Blockchain can be utilized for disseminating information about manufacturing procedures, delivery, assembly and main­ tenance of agricultural products with suppliers and vendors. Fig. 13. Five Use Cases of Blockchain in the precision agriculture. Moreover, blockchain can provide three advantages to the shippers: Transparency Enhancement, Greater Scalability, where Blockchain virtually enables stakeholders from any endpoint to access the supply chain system, and Better Security, where blockchain could potentially protect the system against any tamper and data alteration during the product lifecycle. Table 4 compares between blockchain-based supply chain and tra­ ditional supply chain system in terms of achieving data integrity, the way in which data security is managed, the possibility of data ver­ ification, and government regulations for authenticating processes and activities in the supply chain system. Fig. 15 explains a proposed architectural model in which blockchain can manage agricultural transactions process between resource de­ mands and resource suppliers in a supply chain system. The main role of blockchain in this model is storing new supply chain transactions between many customers’ demands and many suppliers’ products. The customers can create new demand as a new transaction through the decentralized customers’orders engine, and the suppliers can offer new product as a new transaction through the decentralized suppliers’products engine. The smart contract works here as an authenticating protocol between the two engines for verifying and protecting the transaction data patterns between suppliers and customers, then store the valid transactions as a new block in the blockchain. 3) Land Registration: (Barbieri and Gassen, 2017). It can be de­ fined as the process of determining, recording and sharing transactional information about rights, value, and use of land pieces (Anand et al., 2016). The current classical land registry system has a lot of limitations. These systems don’t provide the full authentication for all land trans­ actions between peoples, organizations, and governments. It is esti­ mated that about(70–80%) of land transactions worldwide are not formally registered in any national system (Anand et al., 2016). With Blockchain technology, we became to have a big chance to solve these problems. Blockchain can enhance data security and ensure the authenticity of land registration records. With the transparent, de­ centralized public ledger it becomes easy to store time-stamped land transactions and historical rights of land pieces. Since blockchain does not rely on a single data center, It is able to auto-reject any illegal land transaction. It is able to detect tamper proofs on registered records and protect all land transactions and registry details based on ”colored coins. The colored coins-based protocol can be applied to land regis­ tration by representing the ownership of a piece of land by a single or multiple tokens. The metadata associated with the token can be used to monitor public registry information such as size, GPS coordinates, year built etc. Verifying and tracking the ownership of each token can be executed across the internet using a blockchain explorer software. Proof of Concept (Luckas, 2019) with Ethereum (Vujicic et al., 2018) is a good will be discussed in subSection 4.1. Moreover, some of the prominent blockchain platforms that can be used in managing different sectors in precision agriculture are investigated and discussed in subSection 4.2. 4.1. Blockchain usecases in the precision agriculture Although the research in adopting blockchain technology in the precision agriculture is in its early stages, the research trend explained major five use cases of applying blockchain in the precision agriculture as summarised in Fig. 13. Using blockchain technology in the precision agriculture can introduce new contributions and improve many func­ tions such as monitoring and traceability, transparency, and efficiency at levels of the farmers and the consumers. 1) Farm Overseeing: building smart farms based on IoT sensors (e.g. temperature, humidity, light, crop maturity sensors, etc.) Enable the farmers and stakeholders to digitize the obtained agricultural data from the sensors for different purposes. Utilizing blockchain here will provide more rapid and smooth communication between sensor net­ works. For example, blockchain can be used for monitoring crop storage techniques for preventing post-harvest losses. Moreover, it can be uti­ lized for tracking CO2 concentration for avoiding mold growth invasion (Sam, 2018). Traditional sensors able to detect the potential for losses 3 5 weeks earlier than traditional monitoring techniques do, how­ ever, 52% of the nation’s essential fruits and vegetables being thrown out due to missing the control and monitoring over the supply chain. Blockchain can be utilized also for providing secure communication in Smart Greenhouse Farming (SGF) as depicted in the proposed model in Fig. 14 (Patil et al., 2017). The figure explains a farm overseeing fra­ mework that involves four subsystems: smart greenhouse farm, private blockchain, cloud storage, overlay network and the end-users (farmer (s)). The SGF is equipped with several IoT sensors (e.g. humidity sen­ sors, light sensors, water level sensors, and CO2 sensors) as well as some actuators (such as, LED light, Fan, Heater and sprinkling). All transac­ tions that can be occurred between IoT devices in the SGF can be stored and mined in a private blockchain. Moreover, the secure data com­ munications between SGF, blockchain, cloud storage and end-user (i.e. farmers who can remotely access its SGF using smart devices such as mobiles and computers) can be managed through an overlay network. On the other hand, Blockchain can be used for monitoring water sys­ tems that serve a set of smart farms (Lin et al., 2017) at the same time. 2) Supply Chain: Monitoring processes of the supply chain using a public blockchain ledger adds a great value to agricultural goods and promote the transparency of supply chain processes. Blockchain enables consumers to track agricultural machinery, crops, and livestock for 11 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 14. Blockchain-based smart greenhouse farming model: A proposed model. 10B 15B annually (Galvin, 2017). Utilizing Blockchain in the food industry, consumers will be able to verify the source and safety of their food in seconds. Blockchain could be used to tell consumers that the fruit and vegetables were grown with herbicide. It will provide realtime tracking, authenticating, securing and monitoring functions for the food supply chain process (Ge et al., 2017; Galvez et al., 2018). Blockchain also can introduce good solutions for detecting food fraud and enhance provenance transparency such as organic food verifica­ tion. Although utilizing blockchain technology in food safety is in its early stage, some interesting benefits of integrating blockchain and IoT can be summarized as follows (Tian, 2016): Table 4 A comparison between blockchain-based supply chain and traditional supply chain. Comparative item Blockchain-based supply chain Traditional supply chain Data integrity Data Security Data Verification Government regulations Tamper proof Decentralized protection Achieved using authentication protocol No tamper proof Centralized protection Not achieved without authentication protocol integration example of colored coins in managing the ownership and land transactions (Alexandru and Chami, 2019). The proposed model in Fig. 16 explains how blockchain can be utilized to manage the land registry process in an automated form based on NEM blockchain (New Economy Movement)Bach et al., 2018) and ”InterPlanetary File System (IPFS)” (Benet, 2014). NEM is a P2P cryptocurrency blockchain laun­ ched in 2015 as a novel platform depends on the colored coin XEM which can be mined using Proof of Importance (POI) algorithm (Bach et al., 2018). InterPlanetary File System (IPFS) is a distributed ubiqui­ tous file system that allows users/devices to not only receive but host P2P shared content of land pieces information (Benet, 2014). The land registry process is based on NEM multi-signature accounts that ask N out of M (e.g. 10 out of 30) proofs to create certain land transactions process. The system issue NEM mosaics which are used as confirmation tokens. The system uses a dashboard to monitor all land transaction updates and present them in a visualized form through web APP. The core logic layer is responsible for managing the communications be­ tween the dashboard, API, and IoT land location sensor and IPFS. It also enables to create logical NEM account for land pieces or other real estates through NEM server layer. 4) Food Safety (Lin et al., 2018): In the food industry, Blockchain could transform the entire process and introduce untraditional solutions for food problems. Several studies reported that almost 1 in 10 people in the world fall ill after eating contaminated food every year. More­ over, 68.2% of food safety events happened in China was caused by illegal activities, and the cost of food fraud incidents reaches to 1. Food tracking and monitoring management. 2. Reducing the agri-food loses and logistic costs 3. Detecting food fraud and verifying product information. 4. Protecting agri-food safety information based on integrating RFID technology with blockchain and IoT 5. Maintaining safety and quality of food products. 6. Facilitating the communication between all stakeholders of food industry process. Integrating IoT sensors and electronics chips such as RFID tags are evolving rapidly. So, companies will be able to attach IoT sensors to food products to track and detect food fraud incidents and potential failures. Forwarding these data from IoT sensors to the blockchain can provide standardization, transparency and traceability to the supply chain and help food stakeholders to detect temper-proof. Walmart’s blockchain is a good example of tackling the food safety of Mango and Pork in the food supply chain process (Kamath, 2018). The proposed model in Fig. 17 explains a general architecture model of how block­ chain can be used in the food safety during the major four stages of food supply chain process: food production, food processing, food shipping, and food distribution. 5) Real Time Remittance for small farms: Farmers may need to use a public payment system for receiving real rime remittances from the agricultural organizations or from the governments. With mobile block­ chain systems (Xiong et al., 2018), small farmers become able to execute 12 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 15. Managing supply chain process using blockchain technology: A proposed model. Fig. 16. Managing Land registry and administration using blockchain technology: A proposed model. 13 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 17. Managing food safety using blockchain technology: A proposed model. real-time payments for goods, crops, agricultural services. Moreover, they can receive agricultural remittances through a blockchain mobile APP. Mobile blockchain will make all real-time transactions are faster, trans­ parent and keep farmer information protected. With mobile blockchain APPs, the farmer can get the following benefits (David, 2019): Table 5,6 summarizes the research work in the five blockchain-use cases in the precision agriculture. Fig. 19 depicts the research progress with respect to a number of published papers for each use case. The research analysis result con­ firms that blockchain has more contributions to supply chain proce­ dures than other agriculture use cases. Moreover, farm overseeing, land registry and real-time agricultural remittance transfer still in the early stages of maturity, whereas food safety tracking become a real appli­ cation of blockchain technology. • Cryptocurrency Applications enable farmers to execute payment transactions with crop traders and receive real time remittances. • Electronic Wallet APPs that enable farmer to store and manage their digital assets and money. • Digital crop tracker apps to provide farmers updated information • • 4.2. Blockchain platforms in precision agriculture about the trade rates, cryptocurrency-based transactions, crop market dynamics and a portfolio of various agricultural variables. Retail APPs allowing its Farmer to execute payment transactions through digital currencies Smart Contracts or self-executable protocols APPs allow the farmer to detect any fraud or illegal operations regarding their digital crops or digital assets The rapid growth of using blockchain in precision agriculture leads to developing some platforms that can be used for various agricultural activities. This subsection discusses the most common five blockchain platforms in smart agriculture. 1) Provenance is founded by Jessi Baker in 2013 as the first blockchain platform that supports supply chain activities (Digital Social Innovation, 2019). Provenance enables producers, consumers and re­ tailers to track their products during all stages of the product’s life cycle. It enables every physical product to authenticated by ”a digital passport” that confirms its authenticity and origin for preventing selling fake goods. With Provenance’s trust engine, the participants able to verify their supplier transactions for better supply chain integrity. They can also turn their digital certifications into data-backed marks for the customers to review, then it is forwarded to the blockchain to be stored in a secure, and genuine form. Provenance enables stakeholders to share honest stories about their goods and products in a trustworthy mode. Producers and consumers can show the traceability of each product item through the Provenance’s tracking tool (Provenance, 2019). Moreover, issuing a digital asset for a specific physical product using Provenance and connect to it via a protected tag, e.g. an NFC, will decrease the traceability time from days to seconds, reducing good frauds, providing faster recalls, improving transparency, protecting Integrating blockchain with a remote sensing satellite, data, and mobile money techniques can ensure transparent secure transactions, automated payment remittance transfer between smart farms (Sylvester, 2019). The farmer can execute all financial transactions through a mobile wallet account created on a mobile blockchain such as COIN22 (Sylvester, 2019). As depicted in the proposed model in Fig. 18, farmers can exchange, buy, sell their digital crops through the wallet App created in COIN22 blockchain. When a new transaction occurs between two or more farmers, it should be verified by other farmers who work as verifiers for the new transactions. If the transaction is valid, a new digital token is issued regarding this transaction and stored in a new block that will added to the COIN22-blockchain. On the other hand, based on satellite data sent to COIN22-blockchain, farmers can trace some major indexes of their farms (e.g. soil, water, drought in­ dexes, etc) by using a digital tracer App connected with COIN22. 14 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 18. The architectural model of real time financial transactions between smart farms: A proposed model. brand valueFilatov, 2019). OriginTrail (Konic, 2019) is a similar blockchain platform that developed for data integrity and validation in supply chain activities. 2) AgriDigital is a cloud-based blockchain platform founded in 2015 by a team of Australian farmers and agribusiness professionals (Xu et al., 2019) AgriDigital makes the agriculture supply chain simple, easy and secure between farmers and consumers. The farmers and stake­ holders are able to manage their contracts, deliveries, orders and pay­ ments all in one place and in real-time. The AgriDigital platform has five core subsystems (Agridigital, 2019): based transactions, trusted expertise, such that more than 1500 com­ pany and technical experts prefer to work with IBM blockchain. Moreover, it can bring together regulators, suppliers, consumers, and professionals to work with each other in IBM Blockchain Ecosystem (IBM, 2019). IBM Blockchain enables equal visibility of activities and reveals where an agricultural asset is at any point in time, who owns it and what condition it’s in (Tripoli and Schmidhuber, 2018; Kamath, 2018). 4) Foodcoin (Bitcoin Wiki, 2018) is a new blockchain ecosystem consists of 1000 Eco Farms. It designed to create a global marketplace of food and agricultural products. The Foodcoin system is working through the use of smart contracts and verifying food transactions based on a cryptocurrency called Foodcoin (FOOD). In order to develop the FOOD ecosystem, the FOOD tokens will be created on the Ethereum blockchain, where it can be used as a colored token currency (Rosenfeld, 2012) to purchase or sell food products. The implementa­ tion of the FoodCoin Ecosystem is based on seven subsystems (Bitcoin Wiki, 2018): 1. Transactions. Through this subsystem, farmers and stakeholders able to easily buy and sell several goods 2. Storage. In which, the accounts, payments, orders, delivers, and other sensitive information are digitized and stored 3. Communications, through which, the farmer and consumers can build the connections patterns. 4. Finance, through which, all financial transactions and virtual currency transfers between farmers and consumers can performed. 5. Remit, through which, the real time remittances issued to the farmers can be transferred. 1. Distributed database in a distributed ledger 2. The Foodcoin (FOOD) 3. Multi-functional crypto wallet called (WALLOK). 4. Payment system called (DiPay). 5. Participant verification called DIGID 6. Multi-signature (Multisig)-based smart contracts systems called (Smaco). 7. Food Product authentication system called (Product Orgin ID (PRORID)) The main feature of AgriDigital is the creation of digital assets in the form of tokens. These tokens represent the physical agricultural goods (e.g. tons of grains). Since the digital asset transfer from farmer to the consumer along the supply chain, an immutable data of the physical asset is created using proof of concept protocol (Luckas, 2019). Once a digital asset is issued, users can use the application layer of AgriDigital platform to send/receive data. 3) IBM Blockchain is one of the most common blockchain plat­ forms that is used in agricultural logistics. It is a good choice for opti­ mizing agricultural transactions and global trade relationships (Cook, 2018). What makes IBM blockchain is a popular platform for agri­ cultural stakeholders are: the high security, multi-cloud flexibility- There are also similar blockchain platforms that can be utilized in food industry and supply chain such as ’Ambrosus’, ’TE-Food’, and ’Ripe.io’,Cook, 2018). 5) AppliFarm is a leading blockchain platform which founded in 2017 by Neovia combines (Neovia, 2019). It can be utilized for 15 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Table 5 Summary of the research work of adopting blockchain in smart agricultures. Use Case Research Blockchain Contribution Year Farm Overseeing Lin et al. (2017) 2017 Farm Overseeing Patil et al. (2017) Farm Overseeing Supply Chain De Clercq et al. (2018) Caro et al. (2018) Supply Chain Dujak and Sajter (2019) Supply Chain Li and Wang (2018) Supply Chain Platform with duplicated and shared bookkeeping (2018) Supply Chain Toyoda et al. (2017) Supply Chain Leng et al. (2018) Supply Chain Saberi et al. (2019) Supply Chain Chen et al. (2017) Supply Chain Lu and Xu (2017) Supply Chain Xie et al. (2017) Land Registration Barbieri and Gassen (2017) Land Registration Anand et al. (2016) Land Registration Vos et al. (2017) Land Registration Chavez-Dreyfuss (2016) Food Safety Lin et al. (2019) Food Safety Lin et al. (2018) Food Safety Tse et al. (2017) Food Safety Tian (2016) Monitoring system for water distributions Tracing system for securing sensor communications in the farms Future farming tech. in agriculture 4.0. AgriBlockIoT mechanism for managing Agri-Food supply chain. Blockchain application in supply chain and logistics Monitor system for agricultural products. Provenance system for supply chain trust Blockchain system for the Post Supply Chain Double Blockchain chain system for securing public transactions Review of blockchain in supply chain Supply Chain system for Quality Management Monitoring system the product origins in supply chains Secure blockchain system for tracking products A Blockchain model for managing digital land registry Blockchain system for managing land admiration activities Analysis model for applying blockchain in Land Administration ”Proof of concept”: a blockchain in the Swedish land registry Blockchain system for preventing food data tampering Food tracking technique based on IOT and blockchain Blockchain usecases in securing food supply chain process Tracking system for an agri-foo supply chain in China Research Blockchain Contribution Year Food Safety Galvez et al. (2018) Blockchain in 2018 Real Time Agricultural Remittance Chinaka (2016) Real Time Agricultural Remittance Holotiuk (2019) food Sypply chain Blockchain for managing agricultural products in Africa Blockchain impacts in financial transactions 2018 2018 2019 2018 2018 2017 2018 2019 2017 2017 2017 2017 2016 2017 2016 2019 2018 2017 2016 5. Challenges and open issues Table 6 Summary of the research work of adopting blockchain in smart agricultures (Cont—). Use Case 2017 Adopting blockchain in precision agriculture is in its early phases. Most agricultural projects are less than two years old, and none of those projects are recently more than 1,000 beneficiaries. Moreover, pilot and small scale blockchain projects are started in a limited number of countries around the world. 93% of these projects are either in concept stage or have started a small pilot and 7% of these projects don’t have available information (Galen et al., 2019). Fig. 20 summarises the current status of blockchain-based projects in the precision agriculture. In precision agriculture, Merging blockchain technology with IoT as well as other techniques such as Radio Frequency Identification (RFID) (Ali and Haseeb, 2019), Cyber-Physical Systems (CPS) (Hu et al., 2012), and 4G/5G broadband communications (Dahlman et al., 2016; Agiwal et al., 2019) faces several important challenges and requires more re­ search work (Fernáez-Caramés and Fraga-Lamas, 2018). Developing IoT networks and applications in precision agriculture based on blockchain technology is a complex process and leads to more chal­ lenges and open questions. The next subsection discusses these chal­ lenges in some details. 2016 2017 providing digital proof of animal welfare, and livestock grazing (Carole, 2018). It is able to track livestock data within the animal production sector. Placing linked tags around the cows’necks, that identifies the areas in which they graze, enough digital data can be gathered to guarantee high-quality grazing. For instance, presence in grazing, the number of actual pasture days, pasture changes, etc. Moreover, the Applifarm system can ensure the dependency of monitored livestock farms with animal welfare requirements. Moreover, animal welfare digital data is integrated into the AppliFarm platform and accessible by stakeholders at any time. AppliFarm is well ahead of the market and already operational for #meat, #dairy and #cattle. Another application of Applifarm is the guarantee of tracked livestock farms provides GMOfree feed for their animals. 5.1. Privacy and security challenges Although the P2P design and time stamping-based transactions of blockchain make IoT networks are more secure against a lot of attacks, blockchain-based IoT systems and networks still suffer from four major 16 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Fig. 19. Research progress of blockchain in precision agriculture use cases. attacks: Denial of Services (DoS) attacks (Kolias et al., 2017), Sybil Attacks (Zhang et al., 2014), Eclipse Attacks (Nayak et al., 2016), and Routing Attacks (Apostolaki et al., 2017). DoS is a cyber-attack in which the adversary tries to compromise the availability of an IoT device or a network device to the authenticated users. For example, the attacker can create this attack by sending a fake connection to the blockchain network to deceives the authenticated users and prevents them to mine the valid tokens of a digital asset. DoS can target blockchain-based IoT systems through different types such as Distributed Denial of Services (DoS), in which the adversary uses thousands of fake IP address to flood IoT nodes with streams of bits to make it unable to correctly respond. The common instances of DDoS attacks are SYN flooding, smurf, and Fraggle (Bhattacharyya and Kalita, 2016). An application-layer DDoS attack (Beitollahi and Deconinck, 2012) is another form of DDoS attack where the adversary target applicationlayer functions and features in blockchain-based IoT systems. For ex­ ample, disrupting the farming functions of farmers’accounts for drop­ ping the smart wallet system in COIN22 blockchain (Sylvester, 2019). DDoS Extortion (Dragomiretskiy, 2018), A Challenge Collapsar (CC) attack (Chun-Tao et al., 2012), Permanent Denial-of-Service (PDoS) or Phlasing attack (Leyden, 2019), Shrew Attack (Mahjabin, 2018), Slow Read Attack (Park et al., 2015), Mirai Botnet (Kolias et al., 2017), Teardrop Attack (Shekhar, 2016), and RUDY attack (Najafabadi et al., 2016) are another examples of DoS attacks that can be executed on blockchain-based IoT networks in e-agriculture systems. There are some techniques to limit the probability of success of DoS attacks but it is very tough to completely remove it. One of these techniques is Application Front-End Hardware (O’Dell, 2009). It can be used as smart hardware which works as a firewall for IoT networks for verifying data packets before traffic reaches the blockchain system. Blackholoing and Sinkholing (Xie and Ettema, 2016) is another DoS defense technique. Blackhole Routing can be utilized for protecting blockchain-based IoT system in e- agricultural against DoS attacks where all packet traffic to the attacked IoT device, DNS or IP address is sent to a ”black hole” (e.g. non-existent server). on the other hand, Sinkholing Routing can be used to routes traffic to a valid IP address of IoT device or server which analyzes traffic and rejects bad packets, however, Sinkholing technique is not efficient for most severe attacks. Fig. 20. Recent status of blockchain projects in precision agriculture. 17 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein Intrusion Prevention System (IPS) (Rodas and To, 2015) is another DoS defense technique that works efficiently on attack recognition, how­ ever, it is not able to block behavior-based DoS attacks. One of the serious attacks that targets blockchain-based IoT net­ works in precision agriculture systems is Sybil attacks (Zhang et al., 2014). In this attack scenario, the attacker seeks to use fake IoT nodes or fake sensors by duplicating their identities to set up fake connections in the blockchain-based IoT networks. The honest IoT nodes become unable to distinguish between valid and valid connections. Detecting such attacks is a very hard task, but unfortunately, they do occur. For example, the Swiss-based company Chainalysis that provides block­ chain services created over 250 fake Bitcoin nodes to harvest in­ formation about transactions propagating over the network (Caffyn, 2019). Although there are some countermeasures can be used for de­ creasing the chance of succeeding Sybil attacks, there isn’t a way to eliminate them. Verifying node identities and detecting fake nodes using Finite Automat can be utilized in IoT networks for detecting Sybil nodes (Meligy et al., 2017). Sybil Guard (Yu et al., 2008), Sybil Infer (Danezis and Mittal, 2009) are other techniques that can be utilized to defend against Sybil attack. moreover, Sybil resistant for bitcoin (Bissias et al., 2014) can be used to address Sybil attacks, denial-ofservice attacks, and timing-based inference attacks. Sybil belief (Gong et al., 2014) also is another Sybil attacks defender which based on a semi-supervised learning algorithm. 1) Eclipse Attack (Nayak et al., 2016) is another attack in which the adversary aims to obscure certain nodes from the entire P2P net­ work. The attack scenario monopolizes an IoT node’s connections so that it cannot receive data from any nodes other than the attacking nodes. In contrast to Sybil attacks, Eclipse attacks mainly target single IoT nodes rather than the entire network at once. The attacking node could easily execute double-spending transactions with the blockchain system. This can easily be done by sending a transaction showing proof of payment to the victim IoT node, obscuring it from the network, then finally sending another transaction to the entire network spending the same tokens again. In this way, the victim node becomes isolated and only receives data from the malicious nodes until to drop it (Wst and Gervais, 2016). There have been multiple countermeasures discussed that may reduce the success of eclipse attacks. Most of them propose how a specific IoT node locally stores IP addresses that it will use to later reconnect to the network or set an upper limit on the number of incoming TCP connections (Marcus et al., 2018). However, there is no effective way to completely remove the Eclipse attacks (Fantacci et al., 2009). 2) Routing attack is the last attack model that target blockchainbased IoT networks. The attacker seeks to intercept messages propa­ gating between IoT devices and tamper these messages before sending them to the peers in the network (Wallgren et al., 2013). Routing at­ tacks can be executed through two models: 1) Portioning attacks, in which the adversary divides the network into two or more disjoint groups by hijacking a bridge node between two groups of networks. 2) Delay attack in which the adversary intercepts the propagated mes­ sages, tamper with them and finally propagate them again to the net­ work (Apostolaki et al., 2017). Routing attacks cannot completely be prevented, however, there are some countermeasures that may reduce its success on blockchain-based IoT networks. For example, diversifying the connections between IoT nodes based on dynamic topologies will prevent the attacker to hijack the bridge nodes between two sub-net­ works topologies (Lu, 2014). Another technique is to monitor the net­ work features such as Round-Trip Time (RTT) (Tun and Thein, 2008) and detect anomalous patterns. 3) Privacy preserving is another challenge in blockchain-based IoT network systems (Fernáez-Caramés and Fraga-Lamas, 2018). All IoT devices and participants are authenticated by their public key or a hash value with the blockchain. The anonymity is not ensured and, since all transactions are shared publicly, there is a likelihood for the attacker to analyze such transactions and infer the real identities of the IoT nodes. This makes the privacy is a complex challenge and open problem. For addressing privacy challenges, some limited techniques are proposed for mitigating privacy issues. Permission blockchain (Nikkil et al., 2010) can be utilized for issuing digital certificates for identifying the identities of IoT devices. Extracting device signature automatically can be used for authenticating IoT applications and its users (Dorri et al., 2017). Blockchain-based multi-level mechanisms (Li and Zhang, 2017) can be utilized also to define a set of access lists and access rights for authorizing user/device access. Privacy can also be improved through zero-knowledge proof techniques such as Zerocoin (Miers et al., 2013) and Zerocash (Sasson et al., 2014). However, these techniques still vulnerable to other attack patterns (Peng, 2012). 5.2. Blockchain size and energy consumption Due to the continuous transactions with blockchain, blockchain tends to grow rapidly and block size will increase. This leads to larger download times and the need for a larger memory space for mining purposes (Fernáez-Caramés and Fraga-Lamas, 2018). Moreover, a lot of IoT devices must store large volumes of data that are not interesting to them. this leads to a waste of computational power and resources. This issue can be addressed by using lightweight blockchain (Gruber et al., 2018). However, this approach requires designing a hierarchical and centralized blockchain system. An alternative approach to address the block size growth is miniblockchain (França, 2019). This approach is working through the use of an accounting tree, which registers only the recent status of every node linked to the blockchain. Also, block size has to be scaled according to the bandwidth limitations. Many small transactions would increase energy consumption, while a few large ones may involve big payloads that cannot be processed by some IoT devices (Fernáez-Caramés and Fraga-Lamas, 2018). Moreover, energy consumption is a major factor in blockchain-based IoT computing since most IoT nodes are powered by batteries. Therefore, energy efficiency is a major aspect of keeping longtime computing of IoT nodes. Energy consumption can result during blockchain mining operations (Truby, 2018) and P2P communication (Zhou et al., 2014). Proof of Stake (King and Nadal, 2012) and Proof of Space (Dziembowski et al., 2015) are good algorithms for solving en­ ergy-consuming problems during mining processes. Mini-blockchain (França, 2019) is also a good choice to reduce energy consumption during P2P communications. Moreover, the cryp­ tographic techniques such as Scrypt (Asolo, 2018) or Myriad and multialgorithm mining (CoinBrief, 2018) are faster and thus can be utilized for reducing mining energy consumption. 5.3. Complex technical challenges There are still unsolved technical challenges that can oppose de­ signing blockchain-based IoT network systems in precision agriculture (Nikkil et al., 2010). Some of these challenges can be summarized as follows: 1) Storage capacity and scalability. In the context of IoT-based eagricultural applications the scalability limitations are much difficult to address. Blockchain may appear to be not appropriate for IoT models. With IoT communication, IoT nodes can send gigabytes (GBs) of data in real-time. This attribute represents a solid barrier against the block­ chain and IoT integration model. The known blockchain platforms can only manipulate a few numbers of transactions per second. So this could lead to a potential bottleneck for IoT systems. Moreover, blockchain is not designed to store large amounts of data, So, scaling blockchain to serve thousands of different heterogeneous devices is a big technical challenge (Khan and Salah, 2018). 2) Blockchain Forking. Forking is a common technical problem with blockchain. It occurs when two peers (i.e. miners) add two right blocks to the chain at the same time. This situation is called ”Blockchain forking” (Spanos et al., 2017). All known blockchain protocols solve the 18 Computers and Electronics in Agriculture 178 (2020) 105476 M. Torky and A.E. Hassanein issues that obstacles developing blockchain-IoT systems in precision agriculture. Before this study, a lot of research work discussed the integration between IoT and blockchain as abstract technologies, but this study is one of the first research attempts that investigated how this integration between IoT and blockchain can be implemented in precision agri­ culture domain. Further research work is needed to be carried out in order to validate the proposed blockchain solutions and implement the conceptual models introduced in this study. Moreover, additional re­ search should focus on investigating more blockchain platforms used in precision agriculture and conducting a comparison study under some major criteria in deeper analysis and assessment. Finally, more research work is also needed to examine more closely the link between block­ chain and IoT in additional use cases in precision agriculture tech­ nology. forking problem with a simple rule: The longest chains of blocks is the right one. When we have blockchain fork, some IoT-peers will start mining through one branch of the chain, and the other peers mine through the other chain. Definably, one chain will have more miners than the other, and as such, will insert new blocks to their chain faster. The rest of the miners will then switch over to the longer chain and the forked chain will always die out. Hence, A specific IoT device miner must be programmed to doesn’t execute a transaction on a forked blockchain. The Conventional rule said that it is therefore wise to wait for 6 blocks to really verify and confirm a specific transaction (Cryptohelp, 2018). Blockchain forking can create confusion, fake transactions, technical challenges, and economic uncertainty. Some new blockchains platforms such as Tezos (Fernandes and Alexandre, 2019) suggest formal design structures of blockchain systems to de­ crease the risk of occurring blockchain forking. 3) Latency and Throughput. Due to developing many topologies of IoT networks, developing blockchain-based IoT networks requires rapid processing for a variety of transaction patterns per time unit. This re­ presents a great challenge in IoT networks regarding throughput. For example, Bitcoin’s blockchain can execute a maximum of 7 transactions per second (Vukolic, 2015) while VISA network (VisaNet) able to pro­ cess 100,000 transactions per minute (Vermeulen, 2016). Latency is another challenge related to the time required by the blockchain al­ gorithm to create a novel block in the chain. For example, in the case of Bitcoin, block creation times take a 10-min mean according to Poisson distribution (Fernáez-Caramés and Fraga-Lamas, 2018), while latency requires only a few seconds in the case of VISA blockchain (Vermeulen, 2016). Hence, developing an optimal blockchain-based on IoT network with rapid throughput and low latency represents an open problem. 4) Multi-chain Management. In some cases, professionals and blockchain engineers need to configure more than one blockchain platform for different purposes in an IoT network (Lee and Kim, 2008). For example, in smart agricultural system, Foodcoin (Bitcoin Wiki, 2018) is used to manage food supply chain transactions, COIN22 (Sylvester, 2019) is used to manage financial transactions between farmers, and AppliFarm (Neovia, 2019) can be used to monitor animal welfare, livestock grazing. Configuring more blockchain platforms in a standalone system leads to more security, privacy, scalability, oper­ ability, and monitoring problems. Moreover, the collaborative im­ plementations and the use of collaborative standardization regarding consensus protocols, authentication, authorizations, and encryption algorithms are needed for managing multi-chain platforms (FernáezCaramés and Fraga-Lamas, 2018). 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