What is a blockchain?
In 5 minutes, no jargon.
One word everywhere, one simple idea
You hear “blockchain” about money, art, contracts. Behind the word lies a single idea, and it’s simpler than it sounds: a ledger everyone shares and no one can tamper with. Scroll on — we’ll build it together, step by step.
Agreeing without a trusted third party
When Alice sends money to Bob, a bank usually keeps the accounts and guarantees the operation. But what if no one will — or can — play that central referee? How do strangers agree on “who owns what”? That’s exactly the problem a blockchain solves.
The basic building block
It all starts with a transaction: “Alice gives 2 to Bob.” Alice signs it with a secret key only she holds: no one can impersonate her. This short, signed, tamper-proof line is the basic unit of the whole structure.
Grouping up
Transactions aren’t handled one by one: they’re gathered in batches. Every few minutes, the network bundles the latest operations into a “block” — a page of the great ledger, dated and sealed.
The heart of it
Here’s the clever idea: each block carries a fingerprint of the previous one — a kind of wax seal computed from its contents. Blocks thus form a chain, in order, each hooked to its elder. Hence the name: block-chain.
Everywhere at once
This ledger isn’t locked in a vault: it’s copied identically onto thousands of computers around the world, called “nodes.” Each holds the full copy. There is no original; no one owns it, so no one can seize it.
The lock
What happens if a fraudster edits an old operation? That block’s fingerprint changes instantly; but the next block held the old fingerprint, so the chain no longer fits. Every copy on the network spots the inconsistency and rejects the tampered version. Rewriting the past would mean redoing the entire chain, on the majority of machines, at once: in practice, impossible.
What to remember
A blockchain, then, is a shared ledger whose pages are chained together to make any tampering visible, and copied across a whole network rather than kept by a single authority. The rest — bitcoin, smart contracts, tokens — is just what we choose to write in that ledger.