## 2 Literature Review and Exploration of Concepts  
### Literature Review and Technological Background  
In this section, what a blockchain is and which concepts and technologies help blockchains to emerge are examined. The following questions will be answered thoroughly in the section: what is hashing, and how does the Hashcash algorithm work? What are distributed ledger technologies (DLTs)? What a blockchain is, how Proof of Work (PoW) works, what Ethereum is, and the advantages of using blockchain technology over its legacy counterparts, alongside its inherent limitations and those compared with legacy applications, will be discussed. The notion of an immutable and tamper-proof chain of hashed blocks was initially proposed by [PERSON] and [PERSON] in 1991 [PERSON] and [PERSON] (1991). Their pioneering work aimed at authenticating and timestamping digital documents, involving one-way hashing and timestamping by a pool of clients selected pseudo-randomly. This concept laid the foundation for chaining hash values to verify predecessor transactions. Furthermore, they introduced the idea of consensus mechanisms via distributed ledgers. Distributed ledgers are defined as databases of transactions or assets shared among participants, irrespective of their statuses ([PERSON], 2014) or geographical locations. This consensus mechanism mandates systems to reach a consensus, enhancing resilience against forgery due to the eventual consistency of these systems, even in the face of disruptive attempts to alter ledgers or disrupt networks. A blockchain comprises blocks composed of hashes, data, and nonce values. Hashes result from hashing functions, which convert data into fixed-length strings. Initially, the Hashcash function, proposed by [PERSON] in 1997 [PERSON] (1997), played a pivotal role in generating these hashes. Hash functions are mathematical algorithms with critical properties, including determinism, efficiency, uniform distribution, and the avalanche effect [PERSON] (1997). They find applications in data structures, cryptography, and data verification, serving purposes such as efficient data storage and retrieval through hash tables and ensuring data integrity and authentication in digital signature schemes. Ethereum, another blockchain implementation introduced in 2013 and deployed in 2015 by [PERSON], stands out as an innovative and disruptive technology. Ethereum prioritized smart contracts and Turing completeness over being merely a financial instrument. Smart contracts encode contract terms directly into the code and execute autonomously, eliminating the need for intermediaries and escrows. Ethereum's native cryptocurrency, Ether (ETH), offers transactional value and fuel for smart contract execution. Ethereum initially relied on PoW for consensus, later transitioning to PoS [7]. DLTs, as illustrated in Figure 1, can be considered a type of distributed database management, spreading the database across multiple locations, parties, or devices, either with equal rights or in a master-slave management schema [8]. This approach mitigates single points of failure that result from centralized databases, which can be seen in Figure 2, and ensures the database remains desired. Ethereum's impact on the blockchain ecosystem has inspired various alternative blockchain implementations and platforms, marking a significant shift in the blockchain landscape. In the study titled \"Making Drug Supply Chain Secure, Traceable and Efficient: a Blockchain and Smart Contract Based Implementation\" [9], the complexities and vulnerabilities of the healthcare supply chain are addressed. The authors leverage Ethereum blockchain technology and smart contracts to propose a decentralized track-and-trace system. This approach aims to mitigate issues such as fraud, data inaccuracies, and transparency deficits that are prevalent in the healthcare supply chain. By employing smart contracts and hash functions, the system ensures data protection, automates agreement execution, and provides  
Figure 1: DLT database.