# What is an extended public key (xpub)?

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.

Also called xpub, zpub or master public key.

## Why apps ask for it

Watch-only wallets, portfolio trackers, accounting tools and multisig coordinators use the xpub to follow every address of a wallet as it creates new ones.

## The privacy cost

Whoever holds your xpub sees every past and future address, balance and payment of that wallet, which is far more than any single address gives away.

## The quantum angle

An xpub also reveals the public key behind every address it derives, so a wallet that has shared it has no hidden keys left. With normal derivation, an xpub together with one leaked child private key reveals the parent key as well.

## In Redacted

If you move coins for bunker mode from a wallet whose xpub you have shared, take the fresh address from a new seed. In bunker mode your Redacted account is 25 words of its own and never derived from a wallet key.

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

## Related terms

- [Exposed public key](https://redacted.gg/glossary/exposed-public-key.md): 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.
- [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.
- [Chain analysis](https://redacted.gg/glossary/chain-analysis.md): Chain analysis traces funds on public blockchains and groups addresses into likely owners, using the public record together with outside data such as exchange records, address labels and leaks.
- [Viewing key](https://redacted.gg/glossary/viewing-key.md): A viewing key lets someone see the history of a private account without being able to spend from it, for example to show an accountant or an auditor exactly what happened.

Sources: [BIP 32, Hierarchical Deterministic Wallets](https://github.com/bitcoin/bips/blob/master/bip-0032.mediawiki)
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Page: https://redacted.gg/glossary/extended-public-key/