## 2 Foundations of Blockchain, Ethereum, Smart Contracts, and Digital Wallets  
In this section, we provide an overview of the fundamental technologies relevant to the paper, including blockchain, Ethereum, smart contracts, and digital wallets. Blockchain technology is a relatively new innovation in Information and Communications Technology (ICT), and its adoption across industries is steadily increasing. At its core, the blockchain is a sequential chain of blocks, where each block contains data on multiple transactions. Each newly added block carries a unique identifier, along with the identifier of the preceding block, thereby forming an unbroken chain linking the first block (genesis block) to the most recent one. These identifiers are generated using cryptographic hash functions, which create a unique digital fingerprint based on the block data. This mechanism ensures the integrity and immutability of the stored information, making the blockchain a tamper-resistant and reliable system for recording transactions [8]. Data stored on the blockchain are managed through a peer-to-peer (P2P) network, eliminating the need for a central authority. One of the fundamental processes in a blockchain network is mining, which involves validating and adding new blocks containing transactions to the chain. To ensure that the network nodes can verify the authenticity of the transactions and determine which node should join the next block, consensus mechanisms are implemented [9]. Several consensus algorithms exist, each with its own strengths and weaknesses. The most widely used are as follows:  
* Proof of Work (PoW) [10]--uses cryptographic computations to validate transactions but requires high energy,
* Proof of Stake (PoS) [11]--selects validators based on staked cryptocurrency, reducing energy consumption,
* Proof of Authority (PoA) [12]--depends on trusted validators, making it more centralized but efficient. The choice of a consensus algorithm depends on the specific requirements and objectives of the blockchain-based system, such as scalability, security, and energy efficiency. Figure 1 presents a simplified diagram illustrating the operation of a blockchain. Blockchain has several key properties: (i) immutability--once recorded, data cannot be changed without altering all subsequent blocks and reaching network consensus; (ii) decentralization--each participant holds a full blockchain copy, reducing reliance on a central authority; (iii) transparency--all transactions are visible to participants; and (iv) security--advanced cryptographic techniques ensure data confidentiality, authenticity, and integrity. Depending on access requirements, blockchain networks can be classified into public, private, and hybrid blockchains, each offering varying levels of accessibility and control. The combination of decentralization, immutability, transparency, and security makes blockchain valuable for applications beyond finance, such as supply chain management, digital identity verification, or secure voting. Over time, as blockchain technology began to be utilized beyond the financial sector, the Ethereum platform was introduced, serving as the foundation for the development of dApps [13]. Due to their immutability, transparency, and decentralization, dApps are particularly valuable in use cases where data integrity and resistance to manipulation are of the highest importance. These applications operate on blockchain networks, eliminating reliance on centralized intermediaries and ensuring trustless interactions. At the core of Ethereum lies the Ethereum Virtual Machine (EVM), a decentralized computational environment that ensures the consistency of the network's state across all nodes. Each Ethereum node maintains a copy of this state, enabling a synchronized and secure system. Ethereum operates on an account-based model, where accounts have 20-byte addresses.