The essentials
- A cryptocurrency is an entry in a shared ledger (a blockchain) that many computers keep in step without a central operator.
- Whoever controls the private key controls the coins; transfers are final and cannot be reversed by anyone.
- Prices are highly volatile, protections are thinner than in regulated share or forex markets, and UK retail clients cannot buy crypto derivatives.
How crypto works is simpler than the vocabulary suggests. A cryptocurrency is a record in a shared ledger, the blockchain, which thousands of independent computers keep identical copies of. Nobody holds a coin the way you hold a banknote. What you hold is the ability to sign an instruction that moves an entry in that ledger from one address to another.
The ledger and the network
A blockchain groups transactions into blocks. Each block contains a fingerprint (a cryptographic hash) of the one before it, so the blocks form a chain in which changing an old entry would break every link after it. Computers running the network's software, called nodes, check each new block against the rules: no coin spent twice, every signature valid, no more new coins created than the protocol allows. A block that breaks the rules is simply rejected.
Because every node holds the full history, there is no central database to hack or switch off. That is the core idea. Everything else, from exchanges to stablecoins, is built on top of it.
A transaction, step by step
- You enter the recipient's address and amount in your wallet and choose a fee.
- The wallet signs the instruction with your private key and broadcasts it to the network.
- Nodes check the signature and that the coins are unspent, then pass it on.
- A miner or validator includes it in a block, usually prioritising higher fees.
- Each later block adds a further confirmation, making reversal progressively harder.
At no point does a bank, clearing house or payment company approve or reverse the payment. That is the feature and the risk in one.
Keys, wallets and addresses
Ownership rests on a pair of keys. The private key is a secret number that signs transactions. The public address, derived from it, is where others send coins. A wallet is software or a device that stores private keys and uses them to sign; it does not hold coins itself, because the coins stay on the blockchain.
Most wallets show the key as a recovery phrase of 12 or 24 words. Anyone who has those words has the coins. No legitimate company, support desk or website will ever ask for them. Transfers are final: a payment sent to the wrong address, or to a fraudster, cannot be reversed by a bank or a court order to the network.
How the network agrees: consensus
Thousands of independent computers need a way to agree which block comes next. Two main methods exist.
- Proof of work, used by Bitcoin: miners compete to solve a costly computational puzzle; the winner adds the next block and earns newly issued coins plus transaction fees. Rewriting history would require outspending the rest of the network combined.
- Proof of stake, used by Ethereum since 2022: validators lock up coins as a deposit and are chosen to propose blocks. Dishonest behaviour can cost them part of that deposit.
Coins, tokens and stablecoins
A coin is native to its own blockchain, as bitcoin is to Bitcoin and ether to Ethereum. A token is created by a program (a smart contract) running on an existing blockchain; thousands of tokens run on Ethereum and similar networks. A stablecoin is a token designed to hold a steady value, usually one US dollar, typically by holding reserves. The largest is USDT, which exists on several networks at once.
These are very different things. A coin secures a network; a token may represent almost anything its issuer chooses; a stablecoin is only as sound as its reserves and its issuer.
Exchanges and custody
Most people buy crypto on a trading platform. When you do, the platform usually holds the keys and credits you with a balance in its own records. That is convenient but means you depend on the firm's security, honesty and solvency. Several large platforms have failed or been hacked over the years, and customers were left waiting years for partial repayment, or received nothing.
The alternative is self-custody: moving coins to a wallet whose keys only you hold. That removes platform risk but puts the whole burden of security on you. Lose the recovery phrase and the coins are gone.
Regulation is catching up unevenly. The EU's MiCA regulation now licenses crypto-asset service providers. The UK has banned the sale of crypto derivatives to retail consumers since 2021. Elsewhere, protections vary widely. Our checklist on how to choose a broker applies to crypto platforms too.
Why crypto prices move so much
Most crypto-assets have no earnings, dividends or interest to anchor a valuation. Their price is set by what buyers will pay, which depends on expectations about future use, the supply schedule, regulation and, very often, sentiment. Trading is split across many platforms, some with little oversight, and leveraged products can force large waves of selling when prices fall and positions are closed automatically. The result is a market where moves of 10% in a day are unremarkable and falls of more than half have happened repeatedly.
Crypto prices have also tended to move with appetite for risk in general, falling at the same time as shares during some periods of stress. That undercuts the idea that they reliably diversify a portfolio.
What it costs
Platform trading fees are typically charged as a percentage of each trade, plus a spread. Moving coins on-chain costs a network fee that rises when the network is busy. Withdrawing to a bank can carry its own charge. Illustrative example: buying 0.02 BTC at $60,000 costs $1,200; a 0.1% trading fee adds $1.20, and the same fee applies again when you sell. The crypto profit calculator includes both sides.
The risks, stated plainly
- Volatility. Falls of more than half from a peak have happened repeatedly in the largest crypto-assets.
- Irreversibility. Mistakes and thefts cannot be undone.
- Platform failure. Balances on an exchange are claims on a company, not coins in your control.
- Project risk. Many tokens have lost almost all of their value or been abandoned.
- Fraud. Offers of crypto free of charge, such as "airdrops" that ask you to connect a wallet and approve a transaction, are a common way to drain wallets. So are fake investment apps. See how to spot trading scams.
Records and tax
In many countries, selling crypto, swapping one token for another or spending it can be a taxable event. Tax authorities increasingly receive information from platforms. Keep a record of every purchase, sale, transfer and fee, with dates and values in your home currency, from the start; rebuilding the history years later is difficult. Rules differ widely between countries, so check the guidance of your own tax authority.
Where crypto might fit for a long-term investor
Some long-term investors choose to hold a small amount of crypto; many choose none. If you do, the principles that apply elsewhere apply more strongly here: decide in advance how much you could lose entirely without harm, avoid leverage, understand who holds the keys, and never buy something you cannot explain in a sentence. Price predictions, however confident, are not a reason to buy.
Reader questions
Do I need to buy a whole bitcoin?
No. Bitcoin divides into 100 million units called satoshis, so you can buy a small fraction. The same applies to most crypto-assets.
Is my crypto safe on an exchange?
It depends entirely on the firm. You hold a claim on the platform, not coins under your own control. Check how it is regulated, and understand that compensation schemes rarely cover crypto.
Can a crypto transaction be cancelled?
No. Once confirmed on the blockchain it is final. That is why sending to the right address and network, and never sharing a recovery phrase, matters so much.
Sources
- UK Financial Conduct Authority, ban on crypto-derivatives for retail consumers (2021)
- EU Markets in Crypto-Assets Regulation (MiCA)