How Blockchain Works

Blockchain Technology Basics: A Complete Explanation

Blockchain is one of the most important technological innovations of the 21st century, but also one of the most frequently misunderstood. This page explains how blockchain actually works, from the basics to advanced concepts, without unnecessary jargon.

What Is a Distributed Ledger?

Imagine a standard banking database: a central server stores all transaction records. The bank has complete control, it can freeze an account, reverse a transaction, or (in theory) change a balance. This is a centralized system based on trust in an institution.

Blockchain is the opposite. Instead of a single central server, there is a network of thousands of nodes, each holding an identical copy of the entire database. There is no single “master” server. Every node is a full participant in verifying new transactions. This is a distributed ledger.

On the Bitcoin network, at the time of writing, there are more than 15,000 active nodes distributed around the world. To “hack” Bitcoin, you would have to simultaneously rewrite the database on a majority of these nodes, which is economically and technically nearly impossible.

Blocks and the Chain

Data is not stored randomly; it is organized into blocks. Each block contains:

• Header: Metadata including a timestamp, a nonce (a number used in mining), and the hash of the previous block.
• Body: A list of transactions confirmed in that block.
• Hash: A cryptographic fingerprint of the entire block content.

The key element is the link between blocks: each block contains the hash of the previous block in its header. This link forms a chain, hence “blockchain.” If you tried to alter a transaction in block number 100, you would change that block’s hash, which would disrupt block 101, then 102, and so on up to the current block. The rest of the network would immediately detect this inconsistency and reject the altered version.

Cryptographic Hashing

A hash function converts data of any length into a fixed string of characters (e.g., 64 hexadecimal characters for SHA-256, which Bitcoin uses). Key properties include:

• Deterministic: The same input always produces the same hash.
• One-way: You cannot reconstruct the original data from the hash.
• Avalanche effect: Even the smallest change in the input data results in a completely different hash.

Example: The SHA-256 hash of the text “Blockchain” is always 625da44e4eaf58d61cf048d168aa6f5e492dea166ce1d57ec1f9ce10dc4b67b. Changing one letter produces a completely different hash. This property makes blockchain immutable.

Consensus Mechanisms

Who decides which block gets added to the chain? This is solved by consensus mechanisms:

Proof of Work (PoW) – Bitcoin

Miners competitively solve complex mathematical problems. Whoever finds the solution (a valid nonce) first adds the new block and receives a reward in bitcoins. This process requires enormous computing power, which is intentional, because it makes attacks expensive. The downside is high electricity consumption: the Bitcoin network uses about 120-150 TWh per year, roughly as much as the Netherlands.

Proof of Stake (PoS) – Ethereum

In September 2022, Ethereum switched from PoW to PoS in an event known as “The Merge.” Instead of miners, there are validators who lock up (stake) a minimum of 32 ETH as a guarantee of honest behavior. Validators are randomly selected to propose blocks. If a validator tries to cheat the network, they lose part or all of their staked ETH (slashing). With this transition, Ethereum reduced its energy consumption by more than 99.9%.

Public vs. Private Blockchain

A public blockchain (Bitcoin, Ethereum) is open to everyone: anyone can read transactions, run a node, and participate in the network. Transactions are transparent, every transaction ever executed is visible on a block explorer.

A private blockchain is used by companies for internal purposes: Hyperledger Fabric (IBM), Corda (R3). Access is restricted, but the benefits of immutability and auditability of data are retained.

Smart Contracts

Smart contracts are programs that live on the blockchain and automatically execute when predefined conditions are met. They are written in programming languages such as Solidity (Ethereum), Rust (Solana), or Move (Sui/Aptos). Example: “Automatically transfer 1 ETH from address A to address B as soon as the price of ETH reaches $4,000” without intermediaries, without delays, without the possibility of postponement.

This is the foundation of the entire DeFi ecosystem: lending protocols, decentralized exchanges (DEXs), yield farming platforms, all are smart contracts. But this is also where the risk lies: errors in smart contract code are permanent and can cost millions. That is why there is an entire industry of smart contract auditing.

Conclusion

Blockchain is not just “technology for cryptocurrencies.” It is a new paradigmatic approach to storing and verifying data that eliminates the need for a central authority. Understanding how it works, from hashes and blocks to consensus mechanisms and smart contracts, is a fundamental prerequisite for understanding the security risks in this space.