# Internet of Things and Blockchain Integration: Security, Privacy, Technical, and Design Challenges
## 2 Background and Related Work
### Blockchain Platforms
All the platforms do not use special hardware preparations, while only HLF and Multichain provide ID and key management, enable data confidentiality, and require trusted validators to validate the transactions. It is essential to discuss the concept and functions of the smart contract in the context of BC platforms because they are a requirement of many BioT platforms [45]. A smart contract is defined as a computerized protocol that implements a contract's terms [46]. A smart contract's ability to implement or self-execute contractual clauses is one of its most important characteristics [47]. Furthermore, smart contracts have greatly added to the energy of BC, and this integration has resulted in the second generation of BCs (i.e., BC 2.0). In a trustworthy environment, a mix of automatically executed contracts and no centralized oversight has the potential to revolutionize the way business is conducted today [47]. In \begin{table}
\begin{tabular}{p{113.8 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Features** & **Bitcoin** & **Ethereum** & **HLF** & **Multichain** \\ \hline Access & Public & Public & Consortium & Private \\ \hline Open source & Yes & Yes & Yes & Yes \\ \hline Consensus & PoW & PoS/PoW & PBTF/SIEVE & PBTF/Ripple \\ \hline Crypto currency & Bitcoin & ETH & None & Multicurrency \\ \hline Smart contracts & Bitcoin script & Smart contract & Chain code & Smart filters \\ \hline Special hardware requirement & No & No & No & No \\ \hline Average transaction per second & 7 & 15–20 & 3500 & 200–1000 \\ \hline Hashing algorithm & SHA-256 & Ethash, KECCA-256 & SHAKE256, SHA3 & SHA-256 \\ \hline ID management & No & No & Yes & Yes \\ \hline Key management & No & No & Yes & Yes \\ \hline Trustless operation & Yes & Yes & Trusted validators & Trusted validators \\ \hline Data confidentiality & No & No & Yes & Yes \\ \hline Authentication & No & Medium & High & High \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Comparison of Bitcoin, Ethereum, HLF, and Multichain BCs’ platforms. essence, the smart contract code is stored on the BC, and each contract is known by a unique address, which users may access by sending a transaction to [28]. The BC consensus protocol ensures that the contract is executed correctly. Smart contracts provide several benefits, including cost savings, speed, accuracy, performance, and openness, which have prompted the development of a slew of new applications in a diversity of fields [48]. While Bitcoin includes a simple scripting language, it has proven inadequate, prompting the development of modern BC systems that provide Smart contract features [49]. Ethereum, the most common smart contract BC network, is a BC with a Turing-complete programming language that enables smart contracts and dispersed applications to be defined. Ethereum contracts are written in a stack-based bytecode language at a basic level called \"Ethereum Virtual Machine (EVM) code\" [50]. Financial smart contracts also require details about current events and states in the real world. The so-called oracles have this information. These institutions are essential for the efficient incorporation of smart contracts into the real world, but they add to the challenge by requiring authentication, confidentiality, and oracle trust [51]. Table 3 reports the advantages and disadvantages of these four platforms [42; 43; 44; 10; 13]. The fact that all four most common BC platforms are open-source is a major factor in their success. While HLF and Multichain can provide high scalability and authentication, Bitcoin can provide low levels of authentication and scalability, and Ethereum can provide medium levels of scalability and authentication. Both Bitcoin and Ethereum are linked to a 51% attack level, while this value is 33% for HLF and Multichain. The security level provided by Bitcoin and Ethereum is low since the data are accessible to the public; however, the level is medium for HLF and high for Multichain.