# Process Automation and Blockchain in Intelligence and Investigation Units: An Approach
## 3 Literature Review: Background and Related Work
### Blockchain Technology  
In 2008, [PERSON] introduced the core technology behind Bitcoin [36], the blockchain technology that has gained attention in both business and academic environments. With the growing interest and participation of information technology around the world, blockchain technology is considered one of the most promising technologies in our current era. In December 2018, Statista conducted a statistical survey where from 2019 to 2023, it was possible to observe a considerable increase in the size of the blockchain technology market around the world (Figure 3). According to [PERSON] [37], blockchain is defined as a distributed and decentralized network composed of peers responsible for the storage of the transactions carried out between participants in strict order in an immutable, transparent append-only ledger composed of blocks connected via cryptographic hashes [38; 39; 40; 41]. Through blockchain technology, the idea is to allow actors to trade data or digital assets in a decentralized network made up of peers that stores these transactions in a distributed manner. During these operations, transactions and other information like asset owners are recorded on a ledger. To allow validation of the performed transactions, network nodes employ a 'consensus mechanism' [42; 43]. Transactions stored on the P2P network are first validated by the nodes where, after the agreement of their legitimacy, the transactions are confirmed and stored in blocks. All new block are added to the previous chain of blocks and locked in the chain. The most recent block maintains the information about the current state of the blockchain [44]. The content of the blocks are hashed, forming a unique block identifier stored in the current and subsequent block. Each block stores time-stamped data transactions, where through hash algorithms and public key cryptography, integrity and authenticity are guaranteed. From the deterministic and irreversible result of the hash function, it is possible to verify if the block content has been modified. As each block also stores the hash of the previous block, a link is established between them forming the blockchain. By following the hashes from the current block, the first block creates a specific blockchain, also called the genesis block [45; 46; 47]. An illustrative example of the chain data structure of a blockchain is presented in Figure 4.  
The data (transactions) are digitally signed, broadcasted by participants, and chronologically grouped into blocks. After a new block is verified and included in the ledger, transactions cannot be included without the majority of the participants' consensus [48]. Figure 3: Size of the blockchain technology market around the word (in billion U.S. dollars). Survey period: 2018 to 2023. Publication date: December 2018. Source: statista.com. To maintain data consistency in a distributed ledger, consensus algorithms are used to guarantee data integrity within the existing copies in each peer of the network. For this, a consensus algorithm must be executed to reach an agreement to confirm the order of transactions that reaches an agreement on a suitable decision among nodes [48; 49; 50]. In order to contribute to the formalization and security of relationships over a blockchain network, a smart contract may be used to automate an agreement process between parties of the decentralized network. As first introduced by [PERSON] [51], a smart contract is an application (like a digital protocol) responsible for the verification, execution, and enforcement of business rules that have been agreed by network participants. With these contracts, transactions are securely and automatically executed, which allows for more agility, transparency. and absence of conflicts in operations without having to rely on third parties. By adding functionality to blockchain, business logic and validations are included to transactions [38; 49; 52].