> ## Documentation Index
> Fetch the complete documentation index at: https://mintlify.com/Privacy-Cash/privacy-cash/llms.txt
> Use this file to discover all available pages before exploring further.

# SDK Overview

> Privacy Cash SDK for private transactions on Solana

## Introduction

The Privacy Cash SDK provides a TypeScript/JavaScript interface to integrate private transactions into your Solana applications. Built on zero-knowledge proofs, the SDK enables users to shield and withdraw SOL and SPL tokens privately, breaking on-chain transaction links.

## Key Features

<CardGroup cols={2}>
  <Card title="Private Transfers" icon="shield">
    Shield SOL and SPL tokens into privacy pools using zero-knowledge commitments
  </Card>

  <Card title="Zero-Knowledge Proofs" icon="lock">
    Generate Groth16 proofs for unlinkable withdrawals
  </Card>

  <Card title="UTXO Model" icon="coins">
    Manage private balances with a familiar UTXO-based approach
  </Card>

  <Card title="Merkle Trees" icon="tree">
    Track commitments using efficient sparse Merkle trees
  </Card>
</CardGroup>

## Architecture Overview

The SDK implements a privacy protocol with the following components:

### UTXO Management

The SDK uses a UTXO (Unspent Transaction Output) model inspired by Tornado Cash Nova. Each UTXO contains:

* **Amount**: The value of the UTXO
* **Keypair**: A Poseidon-based keypair (not standard Ed25519)
  * Private key: Random 31-byte value
  * Public key: `PoseidonHash(privateKey)`
* **Blinding Factor**: Random value for commitment hiding
* **Mint Address**: Token mint (SOL or SPL token)
* **Index**: Position in the Merkle tree

### Commitment Scheme

Commitments are calculated using Poseidon hash:

```typescript theme={null}
commitment = PoseidonHash(amount, pubkey, blinding, mintAddress)
```

Commitments are inserted into a Merkle tree maintained by the on-chain program.

### Nullifier Generation

Nullifiers prevent double-spending by marking UTXOs as spent:

```typescript theme={null}
signature = PoseidonSign(privateKey, commitment, index)
nullifier = PoseidonHash(commitment, index, signature)
```

### Zero-Knowledge Proofs

The SDK generates Groth16 proofs that verify:

1. **Merkle proof**: UTXO exists in the commitment tree
2. **Nullifier validity**: Prover knows the private key
3. **Balance conservation**: Input amounts equal output amounts plus fees
4. **External data binding**: Transaction metadata is correctly committed

## Transaction Flow

<Steps>
  <Step title="Shield (Deposit)">
    Create UTXOs with encrypted outputs and insert commitments into the Merkle tree. Users send tokens to the program's token account.
  </Step>

  <Step title="Transfer (Optional)">
    Generate proofs to spend input UTXOs and create new output UTXOs, all within the privacy pool.
  </Step>

  <Step title="Withdraw">
    Prove ownership of UTXOs and withdraw to any recipient address without revealing the deposit source.
  </Step>
</Steps>

## Fee Structure

* **Deposit Fee**: 0% (Free deposits)
* **Withdrawal Fee**: 0.35% of withdrawal amount
* **Fee Recipient**: `AWexibGxNFKTa1b5R5MN4PJr9HWnWRwf8EW9g8cLx3dM`

## Security Considerations

<Warning>
  The SDK uses cryptographic primitives that require careful handling:

  * **Keep private keys secure**: UTXO keypairs control access to funds
  * **Store encrypted outputs**: Needed to reconstruct UTXOs for spending
  * **Verify Merkle roots**: Ensure roots exist in the program's history
  * **Use sufficient anonymity sets**: Wait for more deposits before withdrawing
</Warning>

## Supported Networks

* **Mainnet**: `9fhQBbumKEFuXtMBDw8AaQyAjCorLGJQiS3skWZdQyQD`
* **Devnet**: Available for testing
* **Localnet**: Supported for development

## Next Steps

<CardGroup cols={2}>
  <Card title="Installation" icon="download" href="/sdk/installation">
    Install and configure the Privacy Cash SDK
  </Card>

  <Card title="Basic Usage" icon="code" href="/sdk/basic-usage">
    Learn the core SDK operations
  </Card>

  <Card title="Examples" icon="book" href="/sdk/examples">
    Explore complete integration examples
  </Card>

  <Card title="API Reference" icon="brackets-curly" href="/api-reference/introduction">
    Browse the full API documentation
  </Card>
</CardGroup>