A Bitcoin wallet does not hold coins. It holds the private keys that control them. In the developer documentation's words, wallet programs "create public keys to receive satoshis and use the corresponding private keys to spend those satoshis." Whoever holds the keys, or the recovery phrase that rebuilds them, can spend the bitcoin. Your choice of wallet therefore comes down to two questions: where those keys are kept, and how you will get them back if a device is lost.
What a wallet actually does
The Bitcoin developer guide says the word "wallet" can mean two things: a wallet program, or a wallet file that "store[s] private keys and (optionally) other information related to transactions."
A wallet program does three separate jobs:
- Distributing public keys or addresses, so other people can pay you.
- Signing transactions with your private keys, so you can spend.
- Networking, which means broadcasting signed transactions to the Bitcoin network.
The kinds of wallet differ mainly in whether these three jobs run on one device or are split up. The more of the work that happens on a device connected to the internet, the larger the attack surface for your keys.
Addresses and keys
A Bitcoin address comes from a public key, and you can share it freely. The private key must stay secret, because it authorises spending. Bitcoin.org notes that "all Bitcoin transactions are stored publicly and permanently on the network," while "the identity of the user behind an address remains unknown until information is revealed." Payments are final: "A Bitcoin transaction cannot be reversed, it can only be refunded by the person receiving the funds."
Recovery phrases (BIP-39)
Most modern wallets are hierarchical deterministic (HD) wallets under BIP-32. They derive every key from one root seed. That seed is usually backed up as a mnemonic defined in BIP-39:
- The phrase is 12, 15, 18, 21 or 24 words long and encodes 128 to 256 bits of entropy.
- Each word is an index into a 2,048-word list.
- You can add an optional passphrase. If you do not set one, the specification uses an empty string.
- The seed is derived with PBKDF2 using HMAC-SHA512 and 2,048 iterations.
Bitcoin.org says that with a deterministic wallet, "a single backup of the recovery phrase is sufficient to restore all past and future addresses." It also advises checking how your own wallet handles backups. If you add a BIP-39 passphrase, the phrase alone cannot restore the wallet. Lose the passphrase and the funds are gone.
Types of Bitcoin wallet
The developer guide groups wallets by how they split the work.
Full-service wallets (mobile and desktop apps)
One program generates keys, signs and broadcasts. These wallets are convenient, but the private keys sit on a device connected to the internet. Most phone and desktop wallets work this way. Bitcoin.org's advice is to "keep only small amounts of bitcoins on your computer or mobile device for everyday use."
Most of these apps are lightweight clients. Bitcoin.org says they "let you send and receive bitcoins without downloading the full blockchain." Many use simplified payment verification (SPV), which downloads block headers only and asks full nodes for transaction data. The developer guide lists the costs of this approach:
- A full node "can simply lie by omission," hiding a transaction from the client.
- Requesting specific transactions gives full nodes "a complete view of the public addresses that correspond to the user," which the guide calls "a large privacy leak."
Full-node wallets
A full node downloads and validates every block, starting from the first one. The developer guide calls this the most secure way to operate. Bitcoin Core's download page (version 31.1 at the time of checking) asks for "a one-time download of about 600GB of data" plus about 5–10 GB a month. With pruning enabled, storage drops to roughly 10 GB. The page calls verifying the download against the SHA256SUMS file and its GPG signatures "optional but highly recommended."
Hardware wallets
The developer guide says: "Hardware wallets are devices dedicated to running a signing-only wallet." The device keeps the private keys and signs transactions. A connected phone or computer builds and broadcasts them. Bitcoin.org says hardware wallets offer a strong balance of security and convenience because no other software can be installed on them. They are less convenient than an app, and the device and its recovery phrase both need physical protection.
Offline (air-gapped) signing
An offline wallet is a signing-only wallet on a device that never connects to a network. Unsigned transactions move to it, and signed transactions move back, on removable media. You review and sign each one by hand. This is the cold-storage setup bitcoin.org describes for savings: "storing a wallet in a secured place that is not connected to the network."
Paper wallets
A paper wallet is a printed private key and address, often as QR codes. The Bitcoin Wiki lists the risks:
- Printers: "Many printers have a hard drive for internal storage where the paper wallet will be saved."
- Generation: "Almost all paper wallets are made by websites," which brings in the risks of browser-based wallets.
- Partial spending: People who import the key and spend part of the balance "mistakenly believe the remaining funds are still on the paper wallet when in reality they are in a change address."
The Wiki recommends using a wallet's "sweep" feature, which moves the whole balance at once. A written BIP-39 recovery phrase used with a hardware or software wallet is now the more common way to keep a backup on paper.
Multi-signature
Multi-signature wallets require "multiple independent approvals" before funds can be spent (bitcoin.org). For example, a 2-of-3 setup spreads keys across devices or locations. One stolen or lost key is then not enough to steal or lose the funds.
Which Bitcoin wallet setup fits your use?
Compare the common wallet setups by use, where the private keys sit, and the main trade-off of each.
| Wallet setup | Typical use | Where the private keys sit | Main trade-off | Source |
|---|---|---|---|---|
| Mobile or desktop full-service wallet | Small everyday spending | On an internet-connected phone or computer | Convenient, but keys are exposed to a connected device | |
| Hardware wallet | Larger long-term holdings | On a dedicated signing-only device | Less convenient; device and recovery phrase need physical protection | |
| Offline (air-gapped) signing | Savings in cold storage | On a device that never connects to a network | Each transaction is moved on removable media and signed by hand | |
| Own full node with a hardware signer | Maximum verification and privacy | On the hardware signer | About 600 GB of storage, or roughly 10 GB with pruning | |
| Multi-signature | Shared or high-value funds | Spread across devices or locations, for example 2-of-3 | More setup and more backups to manage | |
| Paper wallet | Printed key kept offline | Printed on paper, often as QR codes | Printer storage and website generation risks; sweep the whole balance when spending | |
| Custodial account | Funds left with a third party | Held by the third party | You rely on that third party to safeguard funds and honor withdrawals |
This table summarises general wallet designs only: it does not review or rank specific wallet products and does not replace backing up your recovery phrase offline.
Choosing by use
| Use | Common setup | Main trade-off |
|---|---|---|
| Small everyday spending | Mobile full-service wallet | Keys on an internet-connected phone |
| Larger long-term holdings | Hardware wallet or offline signing | Less convenient, physical backups needed |
| Maximum verification and privacy | Your own full node, with a hardware signer | About 600 GB of storage unless pruned |
| Shared or high-value funds | Multi-signature | More setup and more backups to manage |
| Funds left with a third party | Custodial account | Bitcoin.org: you "rely on that third party to safeguard them and to honor withdrawals" |
Security checklist
From bitcoin.org's "Securing your wallet" guidance and the FTC:
- Back up the recovery phrase offline and keep copies in more than one physical location. Bitcoin.org warns that "any backup that is stored online is highly vulnerable to theft."
- Encrypt the wallet or device, and do not forget the password: Bitcoin offers very limited password recovery. Encryption does not stop keyloggers.
- Keep wallet software and the operating system updated.
- Move savings to offline storage. Keep only a small spending balance on a phone or computer.
- Never share the recovery phrase. Anyone who has it controls the funds.
- Ignore unexpected links and payment demands. The FTC says: "Never click on a link from an unexpected text, email, or social media message, even if it seems to come from a company you know," and "Only scammers demand payment in cryptocurrency."
- Know there is no safety net. The FTC notes that crypto payments "typically are not reversible" and are "not insured by a government." If a wallet is compromised, "no one can step in to help you recover your funds."
Limitations: this guide covers general wallet design from protocol documentation and consumer guidance. It does not review or rank specific wallet products.
