A blockchain is a digital record of transactions that is securely copied across multiple computers at once. This helps ensure that no single company, bank, or government is in control.
Transactions are grouped into batches called blocks. Each new block is linked to the one before it, forming a chain.
Once a block is added, changing it would mean rewriting every block after it on most of the computers in the network at the same time, which is what makes the record so hard to tamper with.
Blockchain is mostly associated with cryptocurrencies, such as bitcoin or ether. It records who sends and receives the cryptocurrency, allowing the network to track ownership and verify transactions.
Using a blockchain lets strangers agree on who owns what without a middleman. That can mean faster settlement, fewer fees, and trading that runs 24 hours a day instead of stopping when banks or markets close.
How Does a Blockchain Work?
Here’s what happens on a blockchain when you send someone $50 worth of Bitcoin.
The Transaction Is Announced
The sender's digital wallet, an app that holds the secret codes proving they own their coins, broadcasts the payment to the network. That secret code is called a private key. It works like a signature that only the owner can produce.
The Network Checks It
Computers on the network, called nodes, confirm the sender actually has the $50 in Bitcoin. It’s like a bank verifying your balance before approving a payment.
The Payment Joins a Block
Verified transactions are bundled together into a new block. On the Bitcoin network, a new block is added about every 10 minutes.
The Network Agrees and Locks It In
Before a block is added, the network has to agree it’s valid through a set of rules called a consensus mechanism.
Bitcoin’s consensus mechanism uses proof of work, where computers compete to solve a hard puzzle. The first to solve it earns newly created coins.
Ether’s Ethereum network uses proof of stake, where participants lock up their own coins as a deposit they lose if they violate the network’s rules.
The Block Is Chained to the Last One
Each block carries a hash of the block before it, which is a short string of characters that acts like a digital fingerprint of the block’s data.
If anyone changes a single digit in a previous transaction, its fingerprint changes completely. That breaks the link to every block after it and exposes the edit.
Is Blockchain the Same as Bitcoin?
This is a common mix-up. Bitcoin is a digital currency, and its blockchain is the underlying record-keeping system that keeps track of transactions. A good comparison is that email is one use of the internet instead of the internet itself.
Other cryptocurrencies such as Ethereum and Solana use their own blockchains. A bank can also use blockchain to manage transactions on its own financial network.
Is Blockchain Unhackable?
A large, well-established blockchain is extremely hard to rewrite, but that doesn’t make everything connected to it safe.
51% attacks
If someone can control more than half of a blockchain's hashing power, they may be able to alter recent transactions and spend the same cryptocurrency twice. This is called double-spending, and it mainly threatens smaller networks.
Smart contract exploits
Smart contracts are programs that run on blockchains. If there are coding errors, hackers can exploit them to steal funds or manipulate transactions.
Phishing
Hackers use fake emails or websites or messages to trick people into revealing their passwords. They can access victims' wallets and steal their cryptocurrency without hacking the blockchain itself.
What Blockchain Is Used For
Cryptocurrency
Digital currencies like Bitcoin and Ether let people send value directly to each other anywhere in the world at any time.
Tokenized Assets
Tokenization means representing ownership of a traditional asset, like a Treasury bond, a fund, or real estate, as a token on a blockchain. The aim is to improve liquidity, access and security.
Smart Contracts
A smart contract is a program stored on a blockchain that runs automatically when set conditions are met, such as releasing payment once a delivery is confirmed.
Ethereum was built specifically to support these programs, which power lending apps, trading platforms, and digital collectibles.
The Cons of Using Blockchain
Blockchains are slower and more expensive to run than a regular database, because thousands of computers have to store and check the same data.
Proof of work networks like Bitcoin also use large amounts of electricity.
Finally, once data is recorded in a blockchain, it’s not easily modified because it may involve rewriting the code for all the connected blocks.
