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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.

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Key Features

Private Transfers

Shield SOL and SPL tokens into privacy pools using zero-knowledge commitments

Zero-Knowledge Proofs

Generate Groth16 proofs for unlinkable withdrawals

UTXO Model

Manage private balances with a familiar UTXO-based approach

Merkle Trees

Track commitments using efficient sparse Merkle trees

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Architecture Overview

The SDK implements a privacy protocol with the following components:

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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

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Commitment Scheme

Commitments are calculated using Poseidon hash: 
commitment = PoseidonHash(amount, pubkey, blinding, mintAddress)
Commitments are inserted into a Merkle tree maintained by the on-chain program.

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Nullifier Generation

Nullifiers prevent double-spending by marking UTXOs as spent: 
signature = PoseidonSign(privateKey, commitment, index)
nullifier = PoseidonHash(commitment, index, signature)

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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

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Transaction Flow

1

Shield (Deposit)

Create UTXOs with encrypted outputs and insert commitments into the Merkle tree. Users send tokens to the program’s token account.
2

Transfer (Optional)

Generate proofs to spend input UTXOs and create new output UTXOs, all within the privacy pool.
3

Withdraw

Prove ownership of UTXOs and withdraw to any recipient address without revealing the deposit source.

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Fee Structure

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

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Security Considerations

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

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Supported Networks

  • Mainnet: 9fhQBbumKEFuXtMBDw8AaQyAjCorLGJQiS3skWZdQyQD
  • Devnet: Available for testing
  • Localnet: Supported for development

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Next Steps

Installation

Install and configure the Privacy Cash SDK

Basic Usage

Learn the core SDK operations

Examples

Explore complete integration examples

API Reference

Browse the full API documentation

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