Hardware and software wallets, and where the key lives

The software wallet's attack surface is the device it runs on. That includes the operating system, the browser or application the wallet runs inside, any extension with access to the same data, and the backup arrangements the user has made. A key stored in a file that is synchronised to a cloud account is exposed to every compromise of that account. A key typed into a web page is exposed to whatever that page does with it. The failure modes are numerous and they are usually invisible until the coins are gone.

The hardware wallet's attack surface is narrower but not empty. The device itself can be tampered with, particularly if it is bought from a reseller rather than the manufacturer, and a device that arrives with a pre-written seed phrase is a known attack rather than a convenience. The supply chain matters. The firmware can contain defects. The user can still be tricked into confirming a transaction they do not understand, which is why the device's display and the habit of reading it are part of the security model rather than decoration.

There is also a class of attack that neither model addresses: the user's own behaviour. A seed phrase written down and photographed, a phrase entered into a phishing site that imitates wallet software, a transaction confirmed without checking the destination address — these defeat a hardware wallet as thoroughly as a software one. The device raises the cost of a technical attack; it does nothing about a social one.

A software wallet is the right tool for spending. It is always available, it works on a phone, and it can construct a payment in seconds. For a balance that is meant to be used — a working balance for purchases, or funds in transit — the convenience is the point, and the exposure is bounded by how much is held there at any time.

A hardware wallet is the right tool for holding. It is slower to use, it requires the device to be present, and it introduces a backup obligation that the user must actually meet. In exchange it removes the key from the internet-connected machine entirely, which is the single largest reduction in attack surface available to an individual holder. For a balance that is meant to sit for years, that trade is usually worth making.

The two are complements rather than alternatives, and the common arrangement reflects that. A hardware wallet holds the long-term balance, a software wallet holds a small working balance, and the seed phrase for the hardware wallet is stored offline and separately from the device. The seed phrases and private keys page explains what that backup contains, and the multisig page covers what changes when several devices are required to spend.