# Blockchain-Based Lightweight Trust Management in Mobile Ad-Hoc Networks
## 2 Background and Related Work
### Blockchain-Based Trust Management  
Blockchain technology has become popular based on its strong security. This technology emerged from Bitcoin in 2008. Based on its strong security and decentralized management, it has been applied to various types of monetary transactions. In summary, several transactions are performed in a transaction pool. Several nodes attempt to create blocks of unspent transactions to perform a mining process, resulting in a proof-of-work (PoW), which indicates that a block has been created, accepted, and chained into the existing blockchain. After chaining a block into the chain, it is difficult to change information in the block because new blocks can be chained only when a miner obtains the correct nonce that can generate a valid hash value. Hash values are generated based on the nonce that is mined and the previous block hash.  
Owing to its security, potential applications of blockchain in various areas technology has been widely researched. Blockchain-related research on trust management for wireless and ad-hoc network security has recently been published. In [13], a trusted routing scheme based on blockchain technology and reinforcement learning was introduced for wireless sensor networks. In this work, routing activities were stored in a blockchain as transactions for the purpose of non-repudiation while reinforcement learning helped routing nodes choose trusted relay nodes based on information stored in the blockchain. Two types of nodes were defined: validators, which maintain the blockchain; and minions, which track routing information in the network. Validators performed blockchain validation by using proof-of-authority (PoA) to eliminate the resource-consuming tasks in PoW. However, based on the influence of the centralized and predefined validator concept, this method seems to be inappropriate for decentralized MANETs.  
[PERSON] et al. [19] introduced a distributed management system for trust and reward (DMRR) in MANETs. The DMRR utilizes a blockchain to enhance the conventional reputation system, which computes node reputation values based on node behavior and a price-based system, where a sender node gives points to relay nodes. General nodes report information regarding neighboring nodes in the network to specific mining nodes and the mining nodes manage the blockchain. The mining nodes collaborate to create a single target block by eliminating the application of PoW in MANETs. In this work, although the authors have proposed a distributed management system, blockchain management relied on a centralized authority with some predefined trusted nodes because blockchain processes are too heavy to be handled by routing nodes in MANETs.  
A blockchain-based decentralized trust management scheme was also introduced for vehicular networks [20]. Based on the high mobility and dynamic nature of vehicles, vehicular networks require a trustful environment, similar to MANETs. In this paper, the authors have introduced blockchain technology combined with PoW and proof-of-stake (PoS) to regulate the benefits of both mechanisms. Vehicles performed a rating process for other vehicles, while roadside units (RSUs) verified and maintained the TVs in the blockchain network. Because blockchaining was conducted by RSUs, this scheme could be considered as a decentralized system for vehicular networks. However, for completely distributed MANETs without centralization, the application of a more decentralized and lightweight blockchain for trust management is still an important research topic.