# When is a public key exposed?

A public key is exposed once it appears on the chain, usually the first time its address signs a transaction. Until then most addresses show only a hash of the key, which gives a key-breaking attacker nothing to start from.

Also called revealed public key, fresh address or pubkey exposure.

## When the key appears

- Most Bitcoin addresses and every ordinary Ethereum address are a hash of the public key, and the key appears with the first transaction they sign.
- A signed message reveals the key too, even one that never reaches the chain.
- Taproot addresses and the earliest pay-to-public-key outputs show the key from the start.
- Sharing an extended public key with an app reveals the keys of every address the wallet will create.

## Why it matters

An attacker who can recover private keys from public keys, with a quantum computer or with new mathematics, needs the public key first. That is why bunker mode moves funds to addresses that have never signed, and moves them again after every signature.

## In Redacted

Moving into Redacted is one move. Choose bunker mode for it, and your old wallet never has to sign anything again, because your private account no longer depends on its key.

More: [Bunker mode](https://redacted.gg/docs/using-redacted/bunker-mode.md)

## Related terms

- [Bunker mode](https://redacted.gg/glossary/bunker-mode.md): Bunker mode is Justin Drake’s name for a calm, controlled move of crypto to addresses whose public keys are still hidden behind a hash, in case elliptic curves break sooner than expected.
- [ECDSA](https://redacted.gg/glossary/ecdsa.md): ECDSA is the elliptic-curve signature scheme behind most Bitcoin and Ethereum wallets. It proves you hold a private key without showing it, and its security rests on the math of the secp256k1 curve.
- [Address reuse](https://redacted.gg/glossary/address-reuse.md): Address reuse means receiving more than one payment to the same address. Every payment to it is then linked to all the others, and to everyone who sent them.
- [Extended public key](https://redacted.gg/glossary/extended-public-key.md): An extended public key, or xpub, lets an app derive every receiving address of a wallet without being able to spend. Anyone who has it can see all of the wallet’s addresses and their full history.
---

Page: https://redacted.gg/glossary/exposed-public-key/