What Is Blockchain? A Simple, Step‑by‑Step Guide to Its Core Concepts

1. The Essence of Blockchain

Blockchain is essentially a special kind of distributed database. It stores information that can be written to and read from any node in the network, and every node holds a full copy of the database, ensuring consistency through synchronization.

2. The Biggest Feature: No Central Administrator

Unlike traditional databases that rely on a central administrator, blockchain is completely decentralized. This design prevents any single entity from controlling the system, but it also raises the question of how data integrity is maintained without a trusted authority.

3. Blocks

Blockchain consists of a chain of blocks, each similar to a database record. Every block has two parts:

Block Header (Head): stores metadata such as timestamp, the hash of the block’s body, and the hash of the previous block. Block Body (Body): contains the actual transaction data.

Understanding the concept of a hash is crucial for grasping blockchain.

A hash is a fixed‑length fingerprint computed from any input. In blockchain, a SHA‑256 hash is 256 bits long; different inputs always produce different hashes.

Example: the string 123 has the hash a8fdc205a9f19cc1c7507a60c4f01b13d11d7fd0. Only the exact string 123 yields this hash.

Inference 1: Each block’s hash uniquely identifies the block. Inference 2: Changing a block’s content changes its hash.

4. Hash Immutability

The hash of a block is calculated from its header: Hash = SHA256(Block Header). Because the header contains the previous block’s hash and the current block’s body hash, any alteration propagates forward, breaking the chain. To tamper with a block, an attacker would need to recompute hashes for all subsequent blocks, which is practically impossible without controlling >51% of the network’s computing power.

5. Mining

New blocks are added roughly every ten minutes. To add a block, miners must find a hash that satisfies a difficulty target, which requires massive computational effort. The process of repeatedly hashing until a valid result is found is called mining; the hardware performing the work is a mining rig, and its operator is a miner.

6. Difficulty Coefficient

Not every hash qualifies; only those below a target value are accepted. The difficulty coefficient determines how low the target is. For example, block 100 000 has a difficulty of 14484.16236122, making the target extremely small.

The block header also stores a Nonce —the number of hash attempts. For block 100 000, the nonce is 274148111, meaning 274 million attempts were needed to find a valid hash.

7. Dynamic Difficulty Adjustment

To keep the average block time around ten minutes, the protocol adjusts difficulty every 2016 blocks (approximately two weeks). If the average time is shorter than ten minutes, difficulty increases; if longer, it decreases. This ensures a stable issuance rate despite changes in total mining power.

8. Forks

When two miners produce blocks at the same height, a temporary fork occurs. Nodes resolve forks by adopting the longest chain, measured by the number of subsequent blocks (typically six confirmations, about one hour). The chain with the majority of computational power becomes the canonical blockchain.

9. Summary

Blockchain is a decentralized, immutable ledger that has operated reliably since 2009. Its advantages include trustless operation and resistance to tampering, but it suffers from low throughput (minimum ten‑minute confirmation) and high energy consumption due to intensive mining.

No central authority governs the network. Data written to the chain does not require real‑time access. Mining rewards must offset the cost of computation.

If these conditions are not met, traditional databases are more appropriate. Currently, the most viable application of blockchain is cryptocurrency, exemplified by Bitcoin.

10. References

How does blockchain really work? – Sean Han (https://medium.freecodecamp.org/how-does-blockchain-really-work-i-built-an-app-to-show-you-6b70cd4caf7d)

Bitcoin mining the hard way: the algorithms, protocols, and bytes – Ken Shirriff (http://www.righto.com/2014/02/bitcoin-mining-hard-way-algorithms.html)