# The Security of Big Data in Fog-Enabled IoT Applications Including Blockchain: A Survey
## 6 Blockchain: A Versatile Security Solution
Even though blockchain allows anonymous transactions, [PERSON] et al. [156] discussed that pseudonyms still may be pursued. Furthermore,in consideration of IoT growth-rate, bitcoin blockchain will eventually face scalabilty issues. The blockchain is also prone to security hazards; the most common attacks are 51% and majority attacks [157; 158]. \begin{table}
\begin{tabular}{p{113.8 pt} p{113.8 pt}} \hline \hline
**Description** & **Advantages** \\ \hline A distributed IoT network architecture consisting of an SDN base network using the blockchains technique [159] & \(\bullet\) & Improved system’s performance and capacity Threat prevention and protection, data protection, access control, and mitigate network attacks such as cache poising/ARP spoofing, DDoS/DoS attacks \\ \hline An efficient decentralized authentication mechanism based on the public blockchain, Ethereum to create secured virtual zones for secure communication [152] & \(\bullet\) & Not limited to specific IoT services and scenarios Relies on a public blockchain, hence possesses all of its security properties Well defined security requirements for authentication \\ \hline A lightweight BC-based hierarchical architecture for IoT that uses a centralized private Immutable Ledger and a distributed trust to reduce the block validation processing time [149] & \(\bullet\) & Lightweight yet retains privacy and security benefits of classical blockchain security solutions Elimination of overheads associated with conventional blockchain No mining and its processing related delays Low packet and processing overhead \\ \hline A decentralized network model based on blockchain approach for data preserving, data integrity and blocking of unregistered devices using Physical Unclonable Functions (PUFs) and Ethereum [153] & \(\bullet\) & Unique identity to each IoT device Defense against botnets and bogus requests such as Denial of Service (DoS), and Distributed Denial of Service (DDoS) \\ \hline A blockchain-based decentralized, infrastructure-independent proof-of-location technique for location trustworthiness and user privacy preservation [160] & \(\bullet\) & Unlimited identifiers for users to avoid location attacks Blockchain is used to store proofs of location Geographic location verification User location privacy preservation \\ \hline A cloud-based blockchain solution for identifying IoT devices manufacturing provenance while enforcing users privacy preservation using EPID (Enhanced Privacy Identity protocol) of Intel to incentivize IoT devices for data sharing [161] & \(\bullet\) & Support anonymous device commissioning and incentive to IoT devices Ensures privacy-preservation \\ \hline A blockchain-based scheme called Healthcare Data Gateway (HGD) architecture to enable patient to own, control and share their own data easily and securely without violating privacy [150] & \(\bullet\) & No need for trusted third party Ensures privacy-preservation \\ \hline A blockchain-based security and privacy scheme for smart homes [151] & \(\bullet\) & No need for trusted third party Ensures privacy-preservation \\ \hline A blockchain-based security and privacy scheme for smart homes [151] & \(\bullet\) & Low packet, time and energy overheads Ensured availability of devices Resilient against DDoS and linking attacks \\ \hline \hline \end{tabular}
\end{table} 
Table 6: Blockchain-based security solutions in IoT systems. Fog-based IoT systems bring significant privacy and security concerns. The big data produced by a huge number of interconnected IoT device are sensitive and confidential. Thus, it is inevitable to provide end-to-end security and trust. The introduction of blockchain in fog-enabled IoT systems can solve such problems. The design of distributed fog services should be accompanied with state-of-the-art security systems that are capable of working autonomously in real time.