What is a private key?

Think of a stamp that authorizes money transfers: whoever has it can sign, without needing your ID. A private key works in a similar way, except that the “stamp” is mathematical and can be copied without you noticing.

When you send crypto, your wallet uses the private key to create a digital signature. The network checks this signature using the corresponding public key, without ever learning the private key. That way it confirms that the transaction was authorized by the key’s holder. The secret key itself never needs to be sent to the network.

The public key is derived mathematically from the private key and is linked to the address where you receive crypto. Going the other way, i.e. working out the private key from the public key, is computationally infeasible with today’s means, as long as the implementation is correct.

Why it matters

Your crypto isn’t inside the wallet app. Balances and transactions are recorded on the blockchain. The wallet manages the keys that let you use them.

With self-custody, you are responsible for the keys. On a centralized exchange, the company usually manages them. We consider this difference key to understanding who really controls the transfers.

A private key is not a seed phrase. A seed phrase is a series of words from which many wallets derive multiple private keys. A backup of a single key doesn’t necessarily let you recover the entire wallet.

What to watch out for

Never share your private key with customer support, websites or so-called token giveaways. To receive crypto, all you need is the right public address. Screenshots, emails and quick notes in the cloud can expose your secret.

If the key is lost and there is no way to recover it from a secure backup or seed phrase, access can be lost for good. If it leaks, changing the app’s password doesn’t invalidate it. You need to move the affected assets to a new, secure wallet with different keys.