What is a private key?
Owning crypto really means controlling one secret number. Whoever holds it can spend; whoever loses it cannot.
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A private key is a large secret number that controls a crypto wallet. It creates the signatures that authorise transactions, and the public key and address are derived from it. Anyone who has it can spend the funds; if it is lost, there is no reset.
How do private keys, public keys and addresses connect?
Crypto uses asymmetric cryptography, which NIST's blockchain overview explains as a pair of mathematically related keys: a private key that must stay secret and a public key that can be shared. Bitcoin's developer glossary describes the private key as the part of the pair that creates signatures others can verify with the public key. The relationship runs one way. Ethereum's docs say the public key is generated from the private key with the Elliptic Curve Digital Signature Algorithm (ECDSA), and that you cannot derive a private key from a public key.
What does a private key look like?
Most wallets never show you the raw key. They give you a recovery phrase instead, covered in seed phrases explained.
What happens if a private key is lost or stolen?
NIST is blunt: if a private key is lost, any assets tied to it are lost, because regenerating the same key is computationally infeasible; if it is stolen, the attacker has full access. The SEC's investor bulletin on custody gives the same warning and adds a simple rule — never share private keys or seed phrases with anyone.
| Situation | Result |
|---|---|
| You lose the key and every backup | Funds stay on the chain but nobody can move them |
| Someone copies your key | They can move the funds as if they were you |
| You share your address | Nothing bad — it is meant to be public |
Ways to protect keys are in hardware vs software wallets and cold storage.
Questions readers ask
If I use an exchange, do I have a private key?
Usually not one you control. The exchange holds the keys, which the SEC calls third-party custody; you rely on the firm to stay solvent and secure.
Can a private key be changed or reset?
No. There is no administrator who can reset it. If you think a key is exposed, the usual step is to move the funds to a wallet with a new key.
A private key is the whole of ownership in crypto. Keep it secret, back it up somewhere safe and separate, and treat any request for it as an attack. For the bigger picture, read crypto wallets explained.
Sources
- National Institute of Standards and Technology, NISTIR 8202: Blockchain Technology Overview (2018)Primary source
- ethereum.org, Ethereum accounts (developer documentation) (2026)Primary source
- Bitcoin Project (developer.bitcoin.org), Bitcoin developer glossary (2026)Primary source
- Investor.gov, US Securities and Exchange Commission, Crypto Asset Custody Basics for Retail Investors (Investor Bulletin) (2025)Primary source
Educational content only — not financial, investment, legal or tax advice. Crypto-assets are high-risk and you could lose all the money you put in. Rules differ by country; check with your national regulator. See our risk disclosure and editorial policy.
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