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Author | Xiaok Source | Dao Jian Shuo Whisery Word count | 2,509 Reading | About 5 minutes An often overlooked but core difference between the two cryptocurrency giants, Bitcoin and Ethereum, is their account models. Bitcoin adopts the UTXO model, while Ethereum has chosen an account-based model. This is not only a difference in technical implementation, but also directly affects user experience, security and application scenarios.Let’s first review Bitcoin’s UTXO model:Bitcoin UTXO Model: An Elegant Design for Digital Cash As the pioneer of blockchain technology, Bitcoin's account asset model is based on UTXO (unspent transaction output). The core idea of this model is derived from digital cash systems rather than traditional bank accounts. In the UTXO model, a user's balance is not a clear number, but is determined by calculating all unspent transaction outputs belonging to the user. Every Bitcoin can be traced back to its source transaction, forming a complete chain of ownership. This design makes the Bitcoin system more like a distributed ledger network, recording the flow path of every fund. Specifically, you can see what UTXO is? What is the difference between Bitcoin's UTXO model and Ethereum's account model? The privacy protection advantages of the UTXO model are quite significant. Since users can generate an almost unlimited number of addresses, and the correlation between these addresses is difficult to track by the outside world, users' financial privacy is guaranteed to a certain extent. In actual use, many Bitcoin wallets will automatically generate new receiving addresses for users, a mechanism that further enhances privacy. However, the UTXO model also brings considerable barriers to use. Ordinary users often find it difficult to understand why every transaction requires "spending" all coins and then sending the remaining funds back to a new address through the change mechanism. This operating logic is far from the traditional bank transfer experience and requires a certain learning cost. Ethereum Account Model: Innovation for Smart Contracts When building Ethereum, Vitalik Buterin, the founder of Ethereum, chose a different path from Bitcoin - an account-based ledger model. Behind this decision is a deep thinking about the positioning of Ethereum: Ethereum should not only handle currency transactions, but also become a platform for decentralized applications. The account-based model makes the Ethereum experience closer to a traditional bank account. Each account has a clear balance display, and users do not need to care about the specific source of each coin when initiating a transfer. This intuitive design significantly lowers the user threshold and lays a solid foundation for Ethereum to become the most active blockchain application platform in the future. In terms of security mechanisms, the account model naturally resists the double-spend attack problem faced by Bitcoin. Because the system only needs to check whether the account balance is sufficient, it can effectively prevent the same funds from being spent repeatedly, which simplifies the complexity of transaction verification. New challenges for account models: replay attacks Any technical design comes with trade-offs, and Ethereum’s account model introduces a new threat that doesn’t exist in the Bitcoin world—replay attacks. Imagine this scenario: User A transfers 10 ETH to User B, and the transaction is packaged and uploaded to the chain normally. However, malicious user B re-broadcasts the same transaction on the network. If the system does not have appropriate protection mechanisms, user A's account may be deducted by 10 ETH again. Replay attacks form an interesting symmetry with double-spend attacks. A double-spend attack is when the payer attempts to send the same funds twice, while a replay attack is when the receiver tries to make the same payment happen again. In Bitcoin's UTXO model, a replay attack essentially turns into a double-spending attack and is therefore impossible to occur, but in the Ethereum account model, this is a real threat. Ethereum’s Intelligent Protection Network: Nonce Mechanism Faced with the challenge of replay attacks, Ethereum has designed a sophisticated Nonce mechanism. The core idea of this mechanism is to assign a unique sequence identifier to each transaction to prevent any transaction from being executed repeatedly. Each Ethereum account has a Nonce value, which records the number of transactions initiated by the account so far. When a user creates a new transaction, the current Nonce value must be included in the transaction content and signed with the private key. The full nodes in the system will maintain the Nonce status of each account, and only transactions that meet the expected Nonce value will be executed. Specifically, if an account's current Nonce is 20, then the next transaction it initiates must use a Nonce value of 21. When verifying a transaction, the full node will check whether the Nonce value in the transaction is correct. Only after the verification is passed, the transaction will be executed and the locally stored Nonce value will be updated to 21. If someone tries to replay a transaction that has already been executed, the node will find that the Nonce value of the transaction is less than or equal to the current value and refuse to execute it. This mechanism not only solves the problem of replay attacks, but also ensures the reliability of the transaction sequence. Because Nonce values must be used strictly in order, transactions cannot be maliciously reordered, which is particularly important in financial application scenarios. Ethereum’s dual identity system: external accounts and contract accounts Ethereum innovatively designed two different types of accounts, which form the infrastructure of its rich ecosystem. External accounts are accounts controlled by users via private keys, similar to Bitcoin accounts. This type of account has an Ethereum balance and Nonce value, and can actively initiate transactions and call smart contracts. External accounts are the initiators of active actions in the Ethereum network and are the source of activity for the entire system. Contract accounts represent the revolutionary innovation of Ethereum - smart contracts. The contract account not only has balance and Nonce, but also contains code and storage space. They cannot actively initiate transactions and can only execute preset code logic when called by external accounts or other contract accounts. When a contract is deployed to the Ethereum network, the system generates a unique contract address. Through this address, users and other contracts can call the contract's functions. During the execution of the contract, its code remains the same, but the stored state changes with each call. This design allows the smart contract to maintain deterministic execution logic and have the ability to store state. Contract accounts also need the Nonce mechanism, because one contract may call other contracts, forming a complex interaction chain. Nonce here ensures the order and security of calls between contracts. Why does Ethereum give up Bitcoin’s proven UTXO model and instead design a new account system? The answer to this question is rooted in the different visions of the two platforms. Bitcoin is mainly positioned as a peer-to-peer electronic cash system, emphasizing privacy and decentralization. Using a new address for each transaction fits perfectly with this positioning. Ethereum's vision is to become a decentralized application platform, which requires a more stable identity. Smart contract applications such as financial derivatives, decentralized organizations, etc. usually require participants to have persistent and identifiable identities. If addresses are changed frequently like Bitcoin, it will be difficult to establish a trust relationship between contract parties and maintain long-term application status. It is worth pointing out that Ethereum’s account model does not completely sacrifice privacy. Users can still create multiple accounts as needed to spread different trading activities into different accounts. This design provides necessary privacy-preserving flexibility while keeping the primary identity stable. Conclusion Ethereum’s account model represents a key step in the evolution of blockchain technology from a pure currency system to a comprehensive application platform. By introducing an account-based system and a sophisticated Nonce mechanism, Ethereum maintains the core value of the blockchain while providing an underlying architecture that is more in line with application development needs. The implications of this design choice are far-reaching. It not only makes Ethereum the most active smart contract platform, but more importantly, it opens up new possibilities for the entire blockchain industry. From DeFi to NFT, from DAO to the Metaverse, countless innovative applications are built on the Ethereum account model. Understanding the design logic of the Ethereum account system not only helps us use this platform better, but also gives us insight into the evolution direction and future possibilities of blockchain technology. In this new world built by code, accounts are not only the carrier of identity, but also the bridge of value and trust. |
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