# What is a shielded pool?

A shielded pool holds funds as private notes inside a smart contract. Deposits and withdrawals are public, but what happens inside is proved with zero-knowledge proofs and does not reveal who owns what.

Also called privacy pool.

## How it works

A deposit turns public coins into a private note, recorded on-chain only as a commitment. To spend or withdraw, the owner proves with a zero-knowledge proof that they own an unspent note in the pool, and publishes its nullifier so it cannot be spent twice.

## What stays public

The deposit and the withdrawal are ordinary transactions that anyone can see. The privacy comes from the crowd: the more people use the pool, and the less a later action looks like a particular deposit in size and timing, the harder it is to connect the two.

Newer designs, such as the Privacy Pools proposal, also let users show that their funds do not come from a known bad source without revealing their history.

## In Redacted

Redacted’s version is the Reserve, a shared space where every user’s deposits live together as notes that look alike from the outside. Instead of only withdrawing, you act from it through a Spending account: trade, swap, stake, lend and borrow on Rujira.

More: [Reserve and Spending](https://redacted.gg/docs/using-redacted/how-it-works.md)

## Related terms

- [Anonymity set](https://redacted.gg/glossary/anonymity-set.md): An anonymity set is the group of people a given action could have come from. The larger it is, the harder it is to tell who did it.
- [Note](https://redacted.gg/glossary/note.md): A note is a sealed entry on-chain that records coins in Redacted’s Reserve and that only your keys can open. From the outside all notes look alike, whoever owns them and whatever they hold.
- [Nullifier](https://redacted.gg/glossary/nullifier.md): A nullifier is a unique value published when a private note is spent. It lets the chain reject a second spend of the same note without revealing which note was spent.
- [Commitment](https://redacted.gg/glossary/commitment.md): A commitment locks in a piece of data without revealing it. Later it can be opened and anyone can check that it matches, but until then it gives nothing away and cannot be changed.
- [The Reserve](https://redacted.gg/glossary/reserve.md): The Reserve is the shared space where every Redacted user’s deposits live together as sealed notes. From the outside all notes look alike, so an action from the Reserve could have come from anyone who has the same coin in it.

Sources: [Blockchain Privacy and Regulatory Compliance (the Privacy Pools paper)](https://papers.ssrn.com/sol3/papers.cfm?abstract_id=4563364)
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Page: https://redacted.gg/glossary/shielded-pool/