> For the complete documentation index, see [llms.txt](https://vayyl.gitbook.io/vayyl-docs/llms.txt). Markdown versions of documentation pages are available by appending `.md` to page URLs; this page is available as [Markdown](https://vayyl.gitbook.io/vayyl-docs/concepts/privacy-model.md).

# Privacy Model

Vayyl uses a shielded UTXO model: value is represented by notes, notes are represented publicly by commitments, and spent notes are represented by nullifiers.

| Object            | Public role                        | Private data                           |
| ----------------- | ---------------------------------- | -------------------------------------- |
| Note commitment   | Adds value to the commitment tree  | Asset, value, owner key and randomness |
| Merkle root       | Commits to the accepted note set   | The wallet's witness path              |
| Nullifier         | Prevents a second spend            | Which commitment produced it           |
| Output ciphertext | Lets the recipient discover a note | Decrypted note contents                |
| ZK proof          | Proves transaction rules           | Input notes, keys and paths            |

## Privacy properties by action

| Action                     | Intended hidden data                          | Necessarily public data                            |
| -------------------------- | --------------------------------------------- | -------------------------------------------------- |
| Shield                     | New note owner and opening                    | Source, asset, amount, pool, time                  |
| Private transfer           | Sender, recipient, internal values and change | Nullifiers, commitments, relayer, time             |
| Private application action | Private inputs and protected state            | Adapter call and declared public outputs           |
| Unshield                   | Input note and original depositor             | Asset, withdrawal amount, recipient, relayer, time |

## Privacy is a system property

A valid proof does not automatically create practical anonymity. Unlinkability also depends on the number and diversity of users, how long funds remain shielded, amount patterns, timing, relayer behavior, wallet network privacy, and whether output ciphertext can be distinguished.

Vayyl therefore treats pool activity and wallet behavior as part of the protocol design, not as marketing metrics added after the cryptography.


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