Bitcoin Explained: How the First Cryptocurrency Really Works

Money Without a Middleman

Bitcoin is a digital currency that works without any central bank, government or company in charge. When you pay with a bank card, the bank keeps the official record of who owns what and approves every payment. Bitcoin replaces that trusted institution with a network of thousands of computers around the world that all keep a copy of the same record and follow the same rules. No single person or organisation can switch it off, print extra coins or reverse a payment on their own.

Bitcoin was the first decentralized cryptocurrency. "Crypto" refers to cryptography, the mathematics of secure codes, which protects every transaction. Since bitcoin appeared, thousands of other cryptocurrencies have been created, but bitcoin remains the oldest and the best known. By convention, "Bitcoin" with a capital B usually means the network and the system, while "bitcoin" with a small b means the units of money. The currency is often written as BTC, and it has its own symbol, ₿.

This article explains how bitcoin works and why it matters. It is an educational overview, not financial advice: the value of bitcoin rises and falls sharply, and nothing here is a suggestion to buy or sell it.

The Problem Bitcoin Was Built to Solve

Copying digital things is easy. You can send the same photo to a hundred friends and still keep it. That is wonderful for photos, but a disaster for money: if digital coins could be copied, someone could spend the same coin twice. Computer scientists call this the double-spending problem. For decades, the usual solution was to let a trusted central party, such as a bank or a payment company, keep the master list and refuse any duplicate payments.

Bitcoin was not the first attempt at digital cash. In the 1980s and 1990s, the cryptographer David Chaum developed DigiCash, which used clever cryptography but still depended on a central company. Later proposals such as Wei Dai's "b-money" and Nick Szabo's "bit gold" sketched ideas for money without a central authority, and Adam Back's Hashcash introduced a system in which computers had to do a small amount of work to prove they were genuine, originally to fight email spam. Bitcoin combined several of these ideas into a working system for the first time, solving double spending without a central referee.

The Birth of Bitcoin and Its Mysterious Creator

On 31 October 2008, a short paper titled Bitcoin: A Peer-to-Peer Electronic Cash System was sent to an online mailing list about cryptography. Its author signed as Satoshi Nakamoto. The nine-page paper described how a network of computers could agree on a shared record of payments without trusting one another. The timing was striking: the world was in the middle of a severe financial crisis, and trust in large banks was low.

In January 2009, Nakamoto released the first version of the bitcoin software as free, open-source code, which anyone could read, copy and improve. On 3 January 2009 the very first block of the bitcoin record, known as the genesis block, was created. Hidden inside it was a line of text quoting a headline from the British newspaper The Times of that day: "Chancellor on brink of second bailout for banks". Many people read this as a comment on the banking system that bitcoin was meant to offer an alternative to.

Days later, the first bitcoin transaction took place, when Nakamoto sent coins to Hal Finney, a computer programmer who had been one of the first to show interest in the project. For more than a year, bitcoin was mostly a hobby for a small group of enthusiasts and had no clear price at all.

Who Is Satoshi Nakamoto?

Nobody knows for sure. Nakamoto communicated only through emails and forum posts, worked with other developers for about two years, and then stopped appearing in public around 2010 and 2011, handing the project over to other programmers. Many people have been suggested as the real Nakamoto, and some have claimed the title themselves, but none of these claims has been proven. In 2024, a court in the United Kingdom ruled that one prominent claimant, the Australian computer scientist Craig Wright, was not Satoshi Nakamoto. Researchers who have studied the early blockchain estimate that Nakamoto mined roughly a million bitcoins in the first months, and those coins appear never to have been spent.

How Bitcoin Works

The Blockchain: A Shared Public Ledger

At the heart of bitcoin is the blockchain, a public record of every bitcoin transaction ever made. Payments are grouped into batches called blocks. Each new block contains a digital fingerprint, called a hash, of the block before it. This links the blocks into a chain stretching back to the genesis block. If someone tried to secretly change an old transaction, the fingerprint of that block would change, breaking the link to every block after it. Everyone on the network would instantly notice that the altered copy no longer matched.

Computers that keep a full copy of the blockchain and check that every rule is followed are called nodes. Anyone with a suitable computer and internet connection can run one. Because the record is copied across so many independent machines, there is no single point that can be attacked or shut down.

Keys, Addresses and Wallets

Bitcoin uses a kind of cryptography called public-key cryptography. Every user has pairs of keys. A private key is a secret number that works like a password and a signature at the same time. A public key, from which a bitcoin address is created, can be shared openly, a bit like an account number. To send bitcoin, the owner uses the private key to produce a digital signature, and anyone on the network can check that signature using the public key without ever learning the secret.

A bitcoin wallet is the software or device that stores these keys. Strictly speaking, the coins are never "inside" the wallet; they exist only as entries on the blockchain. What the wallet holds is the power to move them. This has a serious consequence: whoever has the private key controls the coins, and if the key is lost, nobody can recover the bitcoins, because there is no bank to call and no password reset.

Mining and Proof of Work

New blocks are added by participants called miners. Miners collect waiting transactions into a candidate block and then race to solve a mathematical puzzle. The puzzle has no clever shortcut: the computer must repeatedly run the block's data through a function called SHA-256, changing a small number each time, until it finds a result below a certain target. This is pure trial and error, and it requires enormous numbers of guesses. The system is called proof of work, because a valid answer proves that real computing effort was spent.

The first miner to find a valid answer broadcasts the block, other nodes quickly verify it, and the block is added to the chain. As a reward, the successful miner receives newly created bitcoins plus the fees attached to the transactions in the block. This reward is the only way new bitcoins come into existence.

The network is designed so that a new block appears roughly every 10 minutes on average. Every 2,016 blocks, which is about two weeks, the difficulty of the puzzle is automatically adjusted. If more computing power joins the network, the puzzle becomes harder; if miners leave, it becomes easier. Proof of work also protects the system: to rewrite history, an attacker would need to control more computing power than the rest of the network combined, which today would be extremely expensive.

A Currency With a Fixed Supply

Unlike ordinary currencies, whose supply is managed by central banks, bitcoin follows a fixed schedule written into its code. There will never be more than 21 million bitcoins. This is one reason supporters sometimes compare bitcoin to gold, a resource that is limited and difficult to extract.

The schedule is controlled by an event called the halving. Every 210,000 blocks, roughly every four years, the reward for mining a block is cut in half:

• 2009: 50 bitcoins per block
• 2012: 25 bitcoins
• 2016: 12.5 bitcoins
• 2020: 6.25 bitcoins
• 2024: 3.125 bitcoins

Because the reward keeps shrinking, new coins are created more and more slowly. The last fractions of a bitcoin are expected to be mined around the year 2140. After that, miners will be paid only through transaction fees.

A bitcoin can be divided into very small pieces. The smallest unit is one hundred-millionth of a bitcoin (0.00000001 BTC), and it is called a satoshi in honour of the creator. This means that even someone who owns only a tiny fraction of a bitcoin can still make payments with it.

From Experiment to Worldwide Debate

The Pizza That Became Famous

One of the first known purchases of real goods with bitcoin happened on 22 May 2010, when a programmer in Florida named Laszlo Hanyecz paid 10,000 bitcoins for two pizzas. At the time, the coins were worth only a few tens of dollars. As the price of bitcoin later rose enormously, the story became legendary, and bitcoin fans now celebrate 22 May as "Bitcoin Pizza Day".

Growing Pains

As bitcoin grew, it ran into serious problems. Because transactions are linked to addresses rather than names, bitcoin is pseudonymous: not fully anonymous, but not directly tied to real identities either. This attracted criminals. The best-known example was Silk Road, an illegal online marketplace that accepted bitcoin until it was shut down by the FBI in 2013. In 2014 Mt. Gox, a Japanese exchange that had handled most bitcoin trading in the world, collapsed after hundreds of thousands of its customers' bitcoins went missing.

Disagreements inside the community also caused splits. For years, each block had a size limit of one megabyte, which restricted how many transactions the network could handle. Some wanted bigger blocks; others preferred to keep blocks small and build extra layers on top. In 2017 the network adopted an upgrade called Segregated Witness, and a group that wanted larger blocks split off to create a separate currency, Bitcoin Cash. Since then, the Lightning Network has been developed as a second layer that allows small, fast payments to be settled off the main blockchain.

Governments Respond

Countries have taken very different approaches. In 2021 El Salvador became the first country to make bitcoin legal tender, alongside the US dollar. The experiment drew worldwide attention but also criticism from international lenders, and in 2025 El Salvador revoked bitcoin's status as legal tender. Other governments went in the opposite direction: China, for example, banned cryptocurrency trading and mining in 2021, and several countries have banned bitcoin entirely. Many others, including the United States and the members of the European Union, allow it but regulate the companies that trade and store it, especially to prevent money laundering.

Criticisms and Challenges

Bitcoin is one of the most debated inventions of the 21st century. The main criticisms include:

• Energy use. Proof-of-work mining uses huge amounts of electricity. Researchers at the University of Cambridge estimate that the whole network uses about as much electricity per year as some medium-sized countries. Supporters reply that part of this energy comes from renewable or otherwise wasted sources; critics argue the environmental cost is still too high.
• Volatility. The price of bitcoin swings dramatically, sometimes rising or falling by large percentages within days. This makes it difficult to use as a stable measure of value for everyday prices or wages.
• Speed and cost. The main network can process only a limited number of transactions per second, far fewer than large card-payment networks, and fees can rise when the network is busy.
• Crime and scams. Although every transaction is public, the pseudonymous design has been used for ransomware payments, fraud and money laundering. On the other hand, investigators have become skilled at tracing transactions on the public blockchain, and many criminals have been caught this way.
• Irreversibility. A bitcoin payment cannot be cancelled. If coins are sent to the wrong address or stolen, they usually cannot be recovered.

Supporters, in turn, value bitcoin's independence from governments, its predictable supply, its openness to anyone with an internet connection, and the fact that no single authority can block a payment. Economists, regulators and technologists continue to disagree about whether bitcoin is best seen as a currency, a speculative asset, a store of value or a technological experiment.

Lesser-Known Facts About Bitcoin

• Bitcoin's code is open source and is maintained by volunteer developers around the world. Changes are adopted only when enough of the network chooses to run the new software.
• A large number of bitcoins are thought to be lost forever because their owners lost their private keys or threw away old hard drives. One man in Wales spent years trying, without success, to get permission to search a rubbish dump for a discarded hard drive holding thousands of bitcoins.
• The ₿ symbol was added to the Unicode standard in 2017, which means it can be typed and displayed on computers and phones just like the dollar or euro signs.
• Mining began on ordinary home computers. Today it is done mostly with specialised machines called ASICs, built for nothing but running the bitcoin puzzle, often in large facilities placed near cheap sources of electricity.
• The blockchain idea that bitcoin introduced has since been borrowed for many other uses, from other cryptocurrencies to experiments in tracking goods and recording digital ownership.

Whatever its future, bitcoin changed the way people think about money. It showed that strangers across the world could agree on a shared record of value using only mathematics, open software and a set of common rules, and it raised questions about trust, privacy and the role of governments that are still being debated today.