What is public key?

A cryptographic value derived from a private key that can be shared to receive funds.

A wallet address is a shortened form of a public key.

The pair is asymmetric on purpose: one direction of the derivation is easy and the other is not feasible. That is what lets you publish something the whole world can use to check your signatures, without giving anyone the ability to produce one.

How it works

1. A wallet generates a private key, which is a very large random number.
2. Elliptic curve multiplication derives the public key from it. Running this backwards, recovering the private key from the public one, is the problem the security rests on and is not computationally feasible.
3. The public key is hashed and encoded to produce an address, which is shorter and carries a checksum so a mistyped character is rejected rather than accepted.
4. When you sign a transaction, the network verifies the signature against the public key. Nothing secret is transmitted or stored on chain.

Modern wallets derive an entire tree of keys from one seed phrase. The extended public key, or xpub, sits at a branch of that tree and can generate every receiving address below it without the ability to spend. That is what makes a watch only wallet possible.

Example

Suppose you set up an accountant with visibility over a business wallet. You give them the extended public key. Their software derives every address the wallet will use and shows every incoming and outgoing transaction, so they can reconcile the books.

They cannot move a single satoshi, because spending requires the private key that never left your hardware device. That asymmetry is the whole design: read access and spend authority are genuinely separable.

The privacy trade is real though. Anyone holding that extended public key can see every address in the branch and therefore your full balance and history, which is more exposure than sharing a single address.

Why it matters when you buy

Sharing an address to receive a withdrawal is safe; sharing a private key or seed phrase is not, and the distinction is the one to hold onto during your first transfer. Public keys are also what make read-only monitoring possible, which is a genuinely useful setup for anyone tracking holdings across devices. Your first crypto wallet and moving crypto off an exchange cover the steps.

Related terms

private key — the secret it is derived from; address — the shortened public form; xpub — the extended key for a whole branch; watch only wallet — read access without spending; seed phrase — the master backup; hd wallet — how key trees are derived.

Questions

Is it safe to share my public key or address?

Yes for receiving. Neither allows anyone to spend. The consideration is privacy, because an address links to everything it has ever done on a public ledger.

Can someone work out my private key from my address?

No. The derivation runs one way through elliptic curve mathematics and hashing, and reversing it is not computationally feasible with any known method or hardware.

What is the difference between a public key and an address?

The address is derived from the public key by hashing and encoding, which makes it shorter and adds a checksum. You share the address; the public key appears on chain when you spend.