Exchanges, Wallets and Custody

How Crypto Trading Actually Works

When someone buys or sells cryptocurrency, that transaction happens on an exchange — a marketplace that matches buyers with sellers and records the trade. Unlike stock markets, crypto exchanges operate around the clock, every day of the year, with no closing bell. The price you see on live crypto pages typically reflects the most recent trade on one or more of these exchanges.

There are two fundamentally different kinds of crypto exchange, and the distinction shapes everything from how a trade is executed to who actually holds the resulting coins. Most beginners start with centralized exchanges; more experienced users often explore decentralized ones.

Centralized Exchanges (CEXs)

A centralized exchange, or CEX, is a company-run platform that operates much like a traditional brokerage. The company maintains an order book — a live list of buy and sell orders — and acts as the middleman that matches them. When you deposit crypto or cash onto a CEX, the exchange holds those assets on your behalf.

CEXs typically offer familiar features: account registration, identity verification, customer support, and fiat currency on-ramps (meaning you can fund your account with regular money like dollars or euros). They usually provide high liquidity — meaning there are enough buyers and sellers that orders fill quickly and at predictable prices. The bid-ask spread on major coins at large CEXs tends to be narrow for this reason.

The trade-off is control. When your coins sit on a CEX, the exchange controls the private keys — the cryptographic passwords that prove ownership of those assets on the blockchain. You have an account balance on the exchange's internal ledger, but you do not hold the coins themselves. This distinction becomes critical when something goes wrong.

The FTX Collapse: A Widely Known Cautionary Tale

In November 2022, FTX — at the time one of the world's largest crypto exchanges — collapsed after it emerged that customer funds had been misused. Users who held coins on FTX found their withdrawals frozen and, in many cases, their assets unrecoverable. The event became the most prominent modern example of counterparty risk in crypto: the risk that the party holding your assets on your behalf fails or acts improperly.

FTX did not represent a flaw in blockchain technology itself — the underlying networks kept running normally. The failure was institutional: a centralized company had custody of user funds and that custody broke down. Economists and market observers widely cite the collapse as the real-world illustration of why the crypto community places such emphasis on self-custody.

Decentralized Exchanges (DEXs)

A decentralized exchange, or DEX, is a trading venue that runs on smart contracts — self-executing code deployed on a blockchain. There is no company in the middle. Trades happen directly between users' wallets, and the protocol's code enforces the rules automatically. You can read more about the broader ecosystem these operate within in the DeFi guide.

Because there is no central operator, a DEX cannot freeze your account or misappropriate your funds in the way FTX did. However, DEXs come with their own complexities: users pay gas fees (transaction costs paid to the blockchain network) on every trade, interfaces can be less intuitive, and liquidity for smaller tokens can be thin, leading to slippage — getting a slightly worse price than expected because the market moved while the transaction was processing.

Wallets: What They Actually Are

The word "wallet" in crypto is slightly misleading. A crypto wallet does not store coins the way a physical wallet holds cash. The coins always exist on the blockchain. What a wallet stores is your private key — a unique cryptographic string that proves you have the right to move those coins. Whoever controls the private key controls the assets, full stop.

A wallet also has a public key, which generates your public address — the string of characters you share with others so they can send you crypto. Think of the public address like an email address (anyone can send to it) and the private key like your password (never share it with anyone).

Hot Wallets

A hot wallet is any wallet connected to the internet. This includes browser extensions, mobile apps, and the internal wallets maintained by exchanges on your behalf. Hot wallets are convenient — you can access and move funds quickly — but their internet connection makes them more exposed to hacking attempts and phishing attacks.

Cold Storage

Cold storage refers to keeping a private key on a device or medium that is never connected to the internet. Hardware wallets — small physical devices, roughly the size of a USB drive, that sign transactions offline — are the most common form. A paper wallet (a private key printed or written on paper and stored physically) is another form, though considered outdated by most practitioners.

Because a cold-storage device is air-gapped (disconnected from any network), an attacker cannot reach it remotely. The risk shifts instead to physical loss or damage, which is why many users store backups of their seed phrase — a human-readable list of 12 or 24 words that can regenerate a private key — in a secure physical location.

Self-Custody vs Exchange Custody

Self-custody means holding your own private keys rather than trusting a third party to hold them. The crypto community encapsulates this in a widely repeated maxim:

"Not your keys, not your coins."

The phrase captures the idea that an account balance on an exchange is ultimately a liability of that exchange — a promise to pay — rather than direct ownership of the underlying asset. If the exchange becomes insolvent, is hacked at the company level, or restricts withdrawals, users holding coins there may not be able to access them.

Self-custody removes that counterparty risk but transfers full responsibility to the owner. A lost or destroyed private key with no backup means the associated funds are permanently inaccessible — no customer support can recover them. There is no equivalent of a bank's forgotten-password reset.

Many participants in crypto markets treat this as one of the most important mechanical concepts to understand, separate from any question of which coins to hold. The Bitcoin guide and the stablecoins guide both touch on custody considerations specific to those assets.

What Market Data Reveals About Custody

Analysts and traders watch on-chain data — publicly readable information recorded on the blockchain — to observe custody patterns in aggregate. When large volumes of Bitcoin or Ethereum move off exchanges onto private wallets, analysts often read that as a sign that holders are moving to self-custody. The reverse — coins flowing onto exchanges — can indicate holders preparing to trade or sell, since most trading still happens on CEXs.

Open interest in crypto derivatives (futures and options) also reflects how much exposure is being held through exchange-custodied margin accounts rather than spot holdings. You can track broader crypto market movements on the live crypto data page and explore market cycle dynamics to put custody flows in context.

Understanding where coins are held — and who controls the keys — is part of reading the crypto market clearly, alongside understanding price, volatility, and Bitcoin dominance.