What Is Blockchain? Demystifying the Core Technology for Everyday Readers

Imagine a small residential community where, for years, a single property management company handled all financial records: maintenance fees, renovation deposits, and public facility rental income. Every year, residents received a cryptic statement with no way to verify whether funds were misused—until 2018, when a group of tech-savvy homeowners proposed a new system: every household would keep an identical copy of the community’s financial ledger, and any change to the ledger (such as a new maintenance expense entry) would require approval from at least 51% of households before being added to the shared record. Once recorded, no entry could be altered or deleted without leaving a clear, traceable mark. This simple, community-driven record-keeping system is a perfect, real-world analog of blockchain technology.

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1.1 The Core Analogy: A Shared Community Ledger

To understand blockchain, we first need to abandon the common misconception that it is an obscure, technical concept only for programmers. At its simplest, a blockchain is a shared, immutable public ledger—a record book that is not stored in a single location or controlled by a single entity, but copied and synchronized across thousands of computers worldwide. Every entry added to this ledger is verified by the network, locked in place with cryptography, and visible to all authorized participants.

Let’s return to our residential community example to break down the core differences between a traditional centralized ledger and a blockchain-based shared ledger: | Traditional Centralized Ledger | Blockchain Shared Ledger | |-------------------------------|--------------------------| | Stored and controlled by the property management company (single entity) | Copied and stored by every household (distributed across all participants) | | The property management company can alter or delete entries without notifying residents | Any alteration requires approval from most households; altered entries will be rejected by the network | | Residents can only see the final statement, not the full transaction history | Every resident can view the full history of all ledger entries at any time | | If the property management company’s server is hacked or fails, the entire ledger may be lost | Even if dozens of household computers fail, the full ledger remains intact on other nodes |

This analogy captures the three foundational value propositions of blockchain: decentralization, immutability, and transparency. Let’s explore each of these in detail, with real-world examples of why they matter for everyday users.

`#blockchain #analogy #distributed-ledger #core-concepts`

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1.2 Three Core Value Propositions of Blockchain

1.2.1 Decentralization: Eliminating Single Points of Failure and Trust Risk

Decentralization is the most defining feature of blockchain, and also the most different from the systems we use in daily life. Almost all traditional financial, administrative, and data systems are centralized: your bank statement is stored on the bank’s server, your student records are stored on your university’s database, and your e-commerce order history is stored on the platform’s cloud server. This centralization creates two major risks: 1. Single point of failure: If the central server is hacked, crashes, or is controlled by malicious actors, all data may be lost or tampered with. In 2022, more than 400,000 depositors of several small rural banks in Henan, China, found their online savings inaccessible overnight, with total frozen funds exceeding 40 billion yuan. The root cause was that the banks’ centralized backend systems were manipulated by internal personnel to hide bad loans, leaving depositors with no way to verify the true status of their funds[^1]. If these deposits were recorded on a blockchain, no single entity could freeze or alter the records without approval from the majority of network participants. 2. Trust dependency: In a centralized system, you have to trust the operator of the system to act honestly. For cross-border remittances, you have to trust your bank to charge a fair fee and transfer funds accurately; for public welfare donations, you have to trust the charity to use funds as promised. Blockchain eliminates this need for blind trust: the rules of the system are pre-written in code, and no participant can change them unilaterally.

> 📌 电子版侧边栏：为什么 decentralization 不等于“没有中心”？ > Many people misunderstand decentralization as “no rules at all”, but in fact, blockchain replaces the single central authority with a set of transparent, collectively agreed rules. For example, the Bitcoin network has no CEO, but all participants must follow the rule that only 21 million bitcoins will ever be issued, and no one can change this rule without the approval of over 90% of network nodes.

1.2.2 Immutability: Making Data Tampering Extremely Costly

Immutability does not mean data can never be changed—it means that altering recorded data requires an extremely high cost, making casual tampering economically unfeasible. This feature is achieved through the unique structure of blockchain: each “block” of data is linked to the previous block via a cryptographic hash value (a unique “fingerprint” generated from the block’s content). If even a single character in a block is altered, its hash value will change completely, breaking the link to the next block. To tamper with a record, an attacker would need to alter all subsequent blocks in the chain, and control more than 51% of the network’s computing power to have their altered chain accepted as the official one.

Let’s take the Bitcoin network as an example to calculate the cost of a 51% attack: As of 2024, the total computing power of the Bitcoin network is approximately 350 EH/s (exahashes per second). To control 51% of the network, an attacker would need to purchase at least 180 EH/s of mining hardware. The most efficient Bitcoin mining machine on the market, the Antminer S19, has a computing power of 110 TH/s (terahashes per second), so the attacker would need approximately 1.64 million units, costing over 3.2 billion yuan at the current price of 20,000 yuan per unit. In addition, the annual electricity cost for running these machines would exceed 2 billion yuan, and the attack would need to be sustained for at least 10 days to rewrite 6 blocks of transaction history. Even if the attacker succeeded, the Bitcoin community could hard fork the network to roll back the tampered transactions, rendering the attacker’s investment worthless.

This is why the Bitcoin network, which has been running for 15 years, has never suffered a successful 51% attack that caused permanent damage. The only successful 51% attack in history occurred on Ethereum Classic (ETC) in 2020, when an attacker spent 500,000 ETC (worth about $5.6 million at the time) to double-spend funds, but the attack only lasted a few hours before the community rolled back the transactions.

`#immutability #hash #51%-attack #security`

1.2.3 Transparency: All Records Are Traceable and Verifiable

Blockchain transparency means that all recorded data is visible to all authorized participants, and every operation leaves a permanent, traceable record. For public blockchains like Bitcoin and Ethereum, all transaction records are completely public: anyone can use a blockchain explorer to query the full transaction history of any address, without needing any permission. For example, you can search for the address `1A1zP1eP5QGefi2DMPTfTL5SLmv7DivfNa`, which is believed to be Satoshi Nakamoto’s address, and view all 50+ bitcoins he received as a mining reward in 2009, as well as all subsequent transfer records.

It is important to note that blockchain transparency does not mean loss of privacy: addresses on public blockchains are pseudonymous, meaning they are not directly linked to real-world identities unless the user voluntarily discloses their identity or