A wallet does not hold coins
The word “wallet” suggests a container with money inside. In blockchain systems that picture is slightly misleading. The assets are not stored in the wallet; they exist as entries on the shared ledger. What a wallet holds is the means to prove control over those entries, namely secret keys.
A more accurate comparison is a key ring rather than a purse. The ledger records that a certain address controls a certain balance. The wallet stores the secret that lets you authorize moving it, and it also reads the ledger so it can show you what is there.
Keys and addresses
Wallets are built on a pair of mathematically linked keys, explained in detail in the article on public key cryptography:
- The public key, or an address derived from it, can be shared. People use it to send you assets, much like an account number.
- The private key must be kept secret. It is used to create a digital signature that approves a transaction.
When you send something, the wallet signs the transaction with your private key. The network checks the signature against your public key. Nobody needs to see the private key itself. The practical consequence is that whoever has the private key effectively controls the assets, with no customer service desk to reverse a mistake in most systems.
Recovery phrases
Many wallets generate a recovery phrase, often called a seed phrase, usually a list of 12 or 24 ordinary words. The phrase is a human-friendly way of writing down the master secret from which the wallet’s keys are derived. If the phone or computer is lost, entering the phrase into a compatible wallet can restore access.
This makes the phrase extremely sensitive:
- Anyone who sees it can typically take everything.
- If you lose it and also lose the device, there is generally no way to recover the contents.
- Legitimate services do not ask you to type it into a website or send it in a message. Requests of that kind are a classic sign of the scams described in online scams.
Types of wallets
| Type | How it works | Main advantage | Main risk |
|---|---|---|---|
| Software (hot) wallet | An app on a phone or computer that is online | Convenient for frequent use | Exposed to malware and phishing |
| Hardware (cold) wallet | A dedicated device that keeps keys offline and signs transactions internally | Keys are isolated from the connected computer | Can be lost, damaged or bought from an untrustworthy source |
| Paper or offline backup | Keys or phrase written down | No electronic exposure | Fire, loss, theft and physical decay |
| Custodial wallet | A company holds the keys for you and shows a balance in your account | Familiar login and recovery options | You rely on the company; its failure or breach affects you |
“Hot” and “cold” simply refer to whether the keys are connected to the internet. Many people use a mix, keeping small amounts in convenient wallets and larger amounts more securely.
Custodial versus self-custody
With self-custody you hold your own keys, which gives control but also full responsibility. With a custodial service the company controls the keys, and access is typically through a username and password, which feels like a bank login. The convenience is real, but you are trusting the provider with security and solvency. Past failures at providers, including data breaches and insolvency, show that this trust can be misplaced. If you use such an account, protections such as two-factor authentication and a password manager are important basics.
What wallets also do
Beyond sending and receiving, wallets often handle:
- Showing balances and transaction history by reading the ledger.
- Estimating the fee needed for a transaction to be accepted.
- Connecting to applications, including smart contracts, so you can approve actions. Approving a request grants real permissions, so read what a prompt actually asks for.
- Managing several kinds of digital assets under one interface.
Note that the same wallet app can usually be reinstalled on another device. The app is replaceable; the key material is what matters.
Practical safety principles
These are general good practices rather than advice tailored to any one person:
- Keep recovery phrases offline, and never photograph them or store them in cloud notes.
- Keep software updated, as described in software updates, since wallet and device bugs are patched regularly.
- Be skeptical of unsolicited messages, links and “support” contacts.
- Check addresses carefully before sending, since transactions are generally irreversible.
- Consider a test with a very small amount first when using something new.
- Do not rely on a single copy of a backup.
Wallets in the wider payments picture
Wallet apps on phones that store payment cards, discussed under contactless NFC, are a different technology. They hold tokens that stand in for card details and rely on banks to process payments, and they can usually be reversed or disputed. Blockchain wallets work differently because there is typically no central party to undo a transfer.
Whatever the type, the main idea is the same: a wallet is a tool for managing keys, and control of those keys is control of the assets.