A private key is a secret 256-bit number that controls your bitcoin. Learn what it looks like, how it creates addresses and how to keep it safe.
A very big secret number
A private key is a randomly chosen number between 1 and about 1.16 × 10^77, roughly the number of atoms in the observable universe. Written in hex it's 64 characters:
e9873d79c6d87dc0fb6a5778633389f4453213303da61f20bd67fc233aa33262(An example only. Never use a key or seed you have seen published.)
What it does
Your private key produces your public key and your addresses, and it creates the signatures that authorise spending.
You can share your public key and addresses safely. Nobody can work backwards to your private key. See Elliptic curve cryptography.
Not your keys, not your coins
Whoever has the private key controls the coins: there is no password reset. In practice, wallets don't show you raw private keys. They back up everything with a seed phrase from which all your keys are derived.
How to keep it safe
- Let a reputable wallet generate it. See Randomness and entropy.
- Keep the seed phrase offline, on paper or metal.
- Consider a hardware wallet so keys never touch an internet-connected computer.
Scams that target your keys
- Fake support asking for your seed phrase "to verify your wallet".
- Fake wallet apps in app stores that send your seed to the attacker.
- "Validation" websites asking you to type your seed.
- Clipboard malware that swaps an address you copied for the attacker's.
No genuine wallet, exchange or explorer, including MyBitcoinExplorer, will ever ask for your private key or seed.
Key takeaways
- A private key is a secret random 256-bit number.
- It controls the coins: anyone who has it can spend them.
- Public keys and addresses come from it, but can't reveal it.
Common questions
Can two people get the same private key?
With proper randomness, the chance is effectively zero.
Where is my private key stored?
Inside your wallet software or hardware wallet, derived from your seed phrase.
Can someone guess my private key?
Not if it was created with proper randomness; the number of possibilities is astronomically large.
What happens if I lose my private key?
Without the key or a seed backup, the bitcoin it controls can't be spent by anyone.