Private key
Your private key is the secret that lets you spend. Whoever knows it controls the funds.
Photo: “Antique Skeleton Keys” by stockerre, CC BY 2.0, via Flickr (edited: cropped and resized).
A private key is the secret half of a key pair: it creates signatures that anyone can check with the matching public key [1]. In Bitcoin it is a 256-bit number [2]. Whoever holds it controls the funds, so it must never be shared [3].
Key points
- 1A private key is a large random number; the public key and address are derived from it in one-way steps.
- 2Signing with it proves you may spend, without revealing the key itself.
- 3Lose it without a backup and the funds are gone; leak it and they can be taken.
What does a private key look like?#
Underneath, it is just a very large number picked at random. Bitcoin’s developer guide describes a private key as a 256-bit number in a range set by the secp256k1 curve [2]. ethereum.org shows it as 64 hexadecimal characters and notes that it can be encrypted with a password [4]. Most people never see their raw key: modern wallets derive keys from a seed phrase instead.
| Step | Value |
|---|---|
| Hexadecimal characters in an Ethereum private key | 64 |
| Bits per hexadecimal character | 4 |
| Total = 64 × 4 | 256 bits (32 bytes) |
The same 256-bit size as Bitcoin’s keys. The range is so vast that guessing someone’s key is not a realistic attack; stealing it is.
How is it different from a public key?#
The public key is computed from the private key and is safe to share; it lets others check your signatures. The process only runs one way: you can derive public keys from a private key but not the other way round [4]. Your address is a further hash of the public key. The full comparison is in private key vs public key.
Which words are related?#
- Seed phrase — words that can regenerate every private key in a wallet.
- Cold wallet — keeps private keys off internet-connected devices.
- Address — what you share instead of any key.
Frequently asked questions#
Is my wallet password my private key?
No. A password usually just unlocks the wallet app on one device. The private key, or the seed phrase behind it, is what actually controls the funds.
Can a private key be changed?
No. If you think a key is exposed, create a new wallet and move the funds to it straight away.
Should I take a screenshot of my key or phrase?
No. ethereum.org warns that screenshots may sync to cloud storage, where hackers look for them [3].
Sources#
Grade A = primary source (regulator, protocol specification, client code, original author). Grade B = expert secondary source used for explanation only.
- Abitcoin.org developer documentation. Bitcoin Developer Glossary, 2026.
- Abitcoin.org developer documentation. Developer Guide: Wallets, 2026.
- Aethereum.org. Ethereum security and scam prevention, 2026.
- Aethereum.org. Ethereum accounts, 2026.
- Abitcoin.org. Some things you need to know, 2026.