# Cloak Shielded Payment

**Cloak Shielded Payment** is the core privacy primitive of Tirai.

It transforms a regular Solana transfer into a **structurally unlinkable** deposit-withdrawal pair, severing the on-chain edge between the project's treasury and the researcher's wallet.

<figure><img src="/files/M63dOPkIYn8e4mhhIMWt" alt="" width="563"><figcaption></figcaption></figure>

## How a Shielded Payment Works

The flow uses three primitives composed by the Cloak SDK:

* **Groth16 zero-knowledge proof** — proves a valid deposit without revealing UTXO contents
* **Poseidon Merkle tree** — accumulates UTXO commitments into a single root
* **Per-deposit viewing key** — issued at deposit time, scoped to one project

Each shielded payment generates exactly:

* One on-chain deposit transaction (visible publicly, pool destination only)
* One claim ticket (delivered off-chain to the researcher)
* One viewing key (held by the project for audit)

## Payment Generation Steps

<figure><img src="/files/4UaAViqPW3alWXgtCj3y" alt="" width="563"><figcaption></figcaption></figure>

When the project clicks **Pay bounty**:

1. **Tirai forwards the request** to `@tirai/api`
2. **SDK builds the proof** — Cloak SDK calls `transact()` with the amount and label
3. **Generate Groth16 proof** — Cloak generates the deposit proof inside the browser
4. **Sign and broadcast** — Phantom (or another adapter) signs the deposit transaction
5. **Confirmation & return** — the transaction confirms on Solana and Cloak returns `{ ticket, viewingKey, signature, feeLamports }`

<figure><img src="/files/XeVGRGeXoC8KG2qRcXpE" alt="" width="563"><figcaption></figcaption></figure>

## What the Project Receives

After a successful payment:

* **Claim ticket** — delivered to the researcher off-chain
* **Viewing key** — stored by the project, shared with their auditor later
* **Transaction signature** — for on-chain verification of the deposit

The project never sees:

* The eventual destination wallet of the researcher
* Whether the researcher chose existing or fresh wallet mode
* The withdrawal transaction signature

## Privacy Guarantees

The shielded payment model guarantees:

* A public observer sees only **Treasury → Cloak Pool**, never **Treasury → Researcher**
* The withdrawal is unlinkable to any specific deposit on chain
* The Merkle tree's anonymity set grows with every new deposit, strengthening privacy over time

This is the cryptographic foundation that makes Tirai possible.


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