What is a private key?

Many wallets are controlled by a seed phrase, but older wallets (and some paper wallets) hold a private key directly. This page explains what that is, what it can do, and why you should use it only within the verified recovery or import procedure of the wallet concerned.

The short answer

A private key is the secret itself. It is one key, usually a long string of letters and numbers (or a printed or exported key file), that can be used to make valid signatures for the corresponding key material. Whether one private key is enough to move assets depends on the wallet, script or contract configuration. The address is safe to share; the private key never is.

The difference from a seed phrase: a seed phrase is a set of words that can restore the deterministic seed of a wallet. The corresponding keys can then be derived from it. A private key is a single separate key. Imported keys or other wallet configurations can fall outside that seed. See what is a seed phrase.

What you can do with it

• With the correct, compatible wallet software, a private key can give technical access to the addresses, outputs or scripts for which that key is sufficient. A single loose private key does not automatically restore a full wallet: other addresses may use other keys, and multisig, smart-contract or other configurations may require additional data.
• It can also sign a transaction, that is why it must stay secret.
• In an estate, a private key on paper or in a file can provide technical access to the part for which that key is sufficient; it does not prove that the whole wallet is accessible and says nothing about legal authority.

What never to do

• Never enter a private key into an arbitrary website, app, online tool or ‘checker’. Only use a private key once you have established in advance that this is the correct import or recovery procedure according to the current official documentation, for example in suitable wallet software or within a controlled specialist recovery environment.
• Never photograph, scan or email it, and never enter it anywhere just because a website or app looks official. First check in the current official documentation of the wallet concerned where and how recovery is supposed to take place. With some hardware wallets you enter recovery words only on the device itself; with other wallets, an official app, software environment or web recovery procedure can be part of the normal recovery process. If what you see on screen differs from the official recovery procedure, or you are unsure, do not enter anything.
• Do not “test” it by importing it anywhere without knowing exactly what you are doing and why.

If you found one in an estate

1. Preserve it exactly as found; note only that it exists and where.
2. Confirm legal authority before anyone uses it, see legal authority vs technical access.
3. Identify the format (WIF, hex, extended private key xprv/yprv/zprv, paper wallet or keystore file) with the wallet format library.
4. If the estate cannot use it, that is a technical access question: wallet recovery: what is realistically possible.

New to these terms? Plain-language definitions are in the crypto inheritance glossary.