Public and Private Keys
A private key is the secret that proves ownership and authorises transactions; the public key, from which the address is derived, can be shared safely.
Crypto has no account manager who checks your ID before a payment. Instead, ownership is proved with mathematics: a pair of linked keys. One is shared with the world so anyone can send to you and check your signatures; the other must never leave your control. Understanding the difference is the foundation of crypto security.
- Category
- Cryptocurrency and Blockchain
- Reading time
- 4 min
- Also called
- Key pair, Asymmetric keys, Crypto keys
- Updated
Keys in plain words
The private key is the secret half of a key pair, used to sign or decrypt.1
The public key can be shared freely; it lets others check signatures made with the matching private key.2
On Ethereum, a user account is made up of a public and private key pair that control account activity.3 Your address is derived from the public key, so it is safe to share. See Counterparty Risk.
How keys work in a transaction, step by step
Generate a key pair
Your wallet creates a private key and its matching public key.
Derive an address
The address is derived from the public key and can be shared to receive funds.
Sign
To send funds, the wallet signs the transaction with the private key.1
Verify
The network uses the public key to verify that the signature matches.2
Control follows the key
An account is controlled by anyone with the private keys.3
Back up and secure
Securing crypto mainly means securing the private keys.4
Worked examples
Example 1 — Sharing an address
Safe to shareYou give a friend your address to receive 0.1 ETH.
| Shared | Address (from the public key) |
| Kept secret | Private key and seed phrase |
| Risk from sharing the address | None to your funds |
Public keys may be made public; they are used to verify, not to spend.2
Example 2 — A leaked private key
$4,000 at riskSomeone sees a photo of your private key. Your wallet holds $4,000.
| Who can spend | Anyone with the key |
| Funds at risk | $4,000 |
Ethereum user accounts are controlled by anyone with the private keys.3
Example 3 — Why guessing is hopeless
Security depends on youA 12-word seed phrase uses words from a list of 2,048.
| Possible combinations | 2,048¹² = 2¹³² ≈ 5.4 × 10³⁹ |
| At 1 trillion guesses per second | Far longer than the age of the universe |
The danger is not guessing but losing or leaking the backup; seed phrases are often the only way to recover a wallet.5
Private key vs. public key
| Aspect | Private key | Public key / address |
|---|---|---|
| Share it? | Never | Yes |
| Used to | Sign and spend | Receive and verify |
| If lost | Funds may be gone for good | Can be recreated from the private key |
| If leaked | Anyone can spend | No direct risk |
Where keys matter
Receiving funds
Share your address, never your private key.
Sending funds
Signing with the private key authorises the transfer.
Self-custody
You are responsible for your keys.
Exchange accounts
The exchange holds the keys for you.
Advantages and disadvantages
Advantages
- Ownership proved without a bank.
- Anyone can verify signatures with the public key.
- Addresses can be shared safely.
- Keys are practically impossible to guess.
Disadvantages
- A lost private key usually means lost funds.
- A leaked key gives full control to the thief.
- No password reset or customer support.
- Phishing targets seed phrases and keys.
Going deeper
Read as far as you need. Each level builds on the one before it.
One secret, one public
Beginner
Accounts are keys
Intermediate
Common mistakes
Sharing the private key
Giving it to 'support' or typing it into a website.
Storing keys online
Keeping them in email, cloud notes or screenshots.
Confusing address and key
Thinking an address is secret or a key is shareable.
No backup
Relying on one device.
Check your understanding
Test yourself before moving on. Each answer comes with an explanation.
Key points to remember
- A private key signs and proves ownership.
- A public key verifies and can be shared.
- Addresses are derived from public keys.
- Whoever holds the private key controls the funds.
- Back up keys offline and never share them.
Frequently asked questions
Is a seed phrase the same as a private key?
Can someone steal funds with my address?
Can a lost private key be recovered?
Further learning
- Counterparty Risk
The trade-off of letting others hold keys.
- Exchange
Custodial key holding.
- Settlement
How signed transactions settle.
- Exposure
How much a leaked key puts at risk.
Sources
This article is written in our own words. The sources below support the specific facts, rules and figures marked with a number in the text. Links open the original publisher’s page.
- NIST CSRC Glossary. Private key (opens in a new tab) Checked .
- NIST CSRC Glossary. Public key (opens in a new tab) Checked .
- ethereum.org. Ethereum accounts (opens in a new tab) Checked .
- FINRA. Crypto Assets (opens in a new tab) Checked .
- ethereum.org. Ethereum wallets (opens in a new tab) Checked .
Educational content, not financial advice. Examples use hypothetical prices and simplified costs; actual fees, margin rules and regulations vary by broker, market and country. We are not affiliated with any publisher linked above. Last reviewed . Report an error or request a source credit.