Blockchain Technology Explained Simply

A blockchain is a shared record of transactions that many computers keep copies of. New records are grouped into blocks, and each block is linked to the one before it. Because every copy must match, nobody can quietly change an old entry. NIST calls blockchains tamper evident and tamper resistant digital ledgers, usually run without a central authority such as a bank, company or government.

What is a blockchain?

Think of a notebook that thousands of people hold identical copies of. When someone pays someone else, every holder writes the entry in the same order. If one person tries to rewrite an old page, their copy no longer matches everyone else’s, so it is ignored.

A blockchain works the same way, but with math instead of trust in a person. Each block holds a group of transactions plus a short fingerprint, called a hash, of the previous block. NIST explains that blocks are chained together because each one contains the hash of the previous block’s header. Change one old block and its fingerprint changes, which breaks every block after it. That is what makes tampering easy to spot.

Bitcoin, described in the 2008 whitepaper by Satoshi Nakamoto, was the first blockchain-based currency. It solved a clear problem: how to pay someone online without a bank in the middle, and without the same coin being spent twice.

How a transaction gets into a block

Here are the steps, based on the process in the Bitcoin whitepaper. Other blockchains differ in detail, but the shape is similar.

1. You sign and send. Your wallet creates a transaction and signs it with your private key. The signature shows you own the coins without revealing the key.
2. The network hears about it. The new transaction is broadcast to the nodes, the computers that run the network. The whitepaper notes that it does not need to reach every node, as long as it reaches many.
3. Nodes collect it into a block. Each node gathers new transactions into a candidate block.
4. A block creator is chosen. On Bitcoin, nodes compete to find a hard proof of work for their block. The first to find it broadcasts the block. (Other systems pick the creator in another way, as the next section explains.)
5. Other nodes check it. The whitepaper says nodes accept a block only if all its transactions are valid and not already spent.
6. The chain grows. Nodes show they accept the block by building the next block on top of it, using its hash as the “previous hash.”

Each new block on top makes the earlier ones harder to change. This is why people wait for several confirmations before treating a large payment as final. The whitepaper also says nodes treat the longest chain as the correct one. If two blocks appear at the same time, the network settles it when one branch becomes longer.

Proof of work vs proof of stake

A blockchain needs a way for strangers to agree on the next block. This is called consensus. The two best-known methods are below.

	Proof of work	Proof of stake
Who creates blocks	Miners who solve a hard puzzle	Validators who lock up coins
What it costs	Computing power and electricity	Coins at risk of being destroyed
What stops cheating	Cheating costs more work than it earns	Cheaters can lose their staked coins
Example	Bitcoin	Ethereum

Proof of work. Miners repeat trial and error to find a number that makes a block’s hash meet a target. Finding it is hard, but checking it is easy for everyone else. Ethereum used proof of work in the past. ethereum.org now describes that version as deprecated.

Proof of stake. ethereum.org explains that validators put capital, in the form of ETH, into a smart contract. They check new blocks and sometimes propose them. If they try to defraud the network, some or all of their staked ETH can be destroyed. To become a validator on Ethereum, a user must deposit 32 ETH and run three pieces of software. Time is divided into slots of 12 seconds, and one validator is picked at random to propose the block in each slot.

Both methods try to make cheating expensive. Which one is better depends on what you value, such as energy use, cost of entry or track record, and both have critics.

Public, private and permissioned blockchains

NIST describes two broad types. In a permissionless (public) blockchain network, anyone can read and write to the blockchain without authorization. Bitcoin and Ethereum are examples. In a permissioned blockchain, participation is limited to specific people or organizations, with finer controls over who can do what. A group of banks sharing a record among themselves would be one case.

A public chain has no single gatekeeper. A permissioned chain trades some of that openness for control and privacy. Neither is better in general. It depends on who needs to trust whom.

Blockchain vs a normal database

	Blockchain	Normal database
Who runs it	Many parties, often with no central owner	One organization
Changing old records	Very hard by design	Easy for the owner with access
Speed and cost	Usually slower and costlier	Usually fast and cheap
Best for	A shared record among parties who do not fully trust each other	Data one trusted party controls
Mistakes	Hard to reverse	Usually fixable by an administrator

If one company can be trusted to keep the records, a normal database is usually the better tool. A blockchain earns its cost when there is no single party everyone trusts. The FTC notes this has a downside for users: crypto payments are typically not reversible, and no one may be able to step in if you send money to the wrong person.

At a glance

This table replaces the old infographic.

Idea	One-line answer
Block	A group of transactions plus the previous block’s hash
Chain	Blocks linked by hashes, so old records are hard to change
Node	A computer that keeps a copy and checks new blocks
Consensus	How strangers agree on the next block
Proof of work	Agreement by computing effort
Proof of stake	Agreement by locked coins that can be destroyed
Public chain	Anyone can read and write
Permissioned chain	Only approved parties take part

Limits to know

A blockchain protects the record, not you. A wallet password you lose cannot be reset by a company. A payment to a scammer cannot be undone. Public chains show transaction details to everyone, and wallet addresses can sometimes be linked to people, as the FTC points out. If you are new to crypto, learn the scam signs in our guide on how to spot fake cryptocurrency.

Blockchain is also not the same as a coin’s value. To read size and supply figures, see the trader’s guide to market caps. For real uses beyond money, read about practical applications for blockchain technology, and look up any unfamiliar word in the crypto dictionary.

This article is general education and not financial advice.