Blockchain is the engine under almost every cryptocurrency. Strip away the hype and it is simply a way for a group of computers that do not trust each other to agree on a single, tamper-resistant record of events.
1. Blocks and the chain
Transactions are bundled into a block. Each block carries a digital fingerprint called a hash, plus the hash of the block before it. Because every block points back to the last one, they form a chain. Alter a single old transaction and its hash changes, which breaks every block after it — making tampering obvious to everyone.
2. Hashing — the tamper alarm
A hash function takes any data and produces a fixed-length string. Change one character of the input and the output looks completely different. Blockchains use hashing to seal each block so that history cannot be quietly rewritten.
3. Nodes — the distributed ledger
Thousands of computers, called nodes, each store a full copy of the chain. There is no master server. If one node disappears or lies, the others still hold the truth. This is what people mean by "decentralized."
4. Consensus — agreeing on the next block
How does the network decide whose block comes next? Two common methods:
- Proof of Work (mining): computers race to solve a hard math puzzle. The winner adds the next block and earns a reward. Used by Bitcoin.
- Proof of Stake (staking): participants lock up coins as collateral and are chosen to validate blocks. Far less energy-intensive. Used by Ethereum and many newer networks.
Public vs. private blockchains
Public chains (Bitcoin, Ethereum) are open to anyone. Private or "permissioned" chains are run by a known group — useful for businesses tracking supply chains or settlements. Both share the same core mechanics.
Beyond currency
Because a blockchain is really a shared, trustworthy database, people use it for more than money: digital ownership records, supply-chain tracking, voting experiments, and smart contracts — programs that run automatically when conditions are met.
Key takeaways
- Blocks are chained together with hashes, making tampering detectable.
- Many independent nodes each keep a full copy — no central server.
- Consensus (proof of work or stake) decides the next block.
- The same technology powers far more than just currencies.