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Introduction

Confidential transfers within your application powered by Fairblock​

The Stabletrust SDK provides a simple, robust interface for executing confidential transfers using homomorphic encryption and zero-knowledge proofs. It enables developers to integrate confidentiality features directly into their apps—securing token deposits, private transfers, and withdrawals—without requiring deep cryptographic expertise.

What it does​

  • Deposit: Convert public ERC20 tokens into a confidential encrypted balance.
  • Transfer: Execute private transfers without leaking transaction amounts or wallet balances to the public.
  • Withdraw: Move funds seamlessly from the confidential layer back to public ERC20 tokens.

What you can build​

Privacy by default unlocks new use cases for open finance that institutions and enterprises require. Applications you can build include:

  • Confidential payroll apps: Stream salaries to employees and contractors without publishing compensation onchain.
  • Confidential token launchpads: Allow participants to contribute privately, hiding contribution sizing from competitors or bots.
  • Web wallets with confidential transfers built in: Give everyday users privacy by default for their transactions and asset balances.
  • x402 payments with confidential transfers: Perform fast, confidential micro-payments for subscriptions, APIs, or AI agents.
  • Treasury management: Applications for DAOs and funds to move capital without broadcasting their strategy to the market.

Installation​

You can install the Stabletrust SDK into your project via npm or yarn:

# Using npm
npm install @fairblock/stabletrust

# Using yarn
yarn add @fairblock/stabletrust

Join Confidential Builders Program​

Apply to build on Fairblock’s StableTrust SDK and pioneer the next generation of confidential transfers. https://build.fairblock.network/

Supported Networks​

Currently, the Stabletrust SDK supports confidential transfers on the following testnet networks:

  • Ethereum Sepolia (11155111)
  • Arbitrum Sepolia (421614)
  • Base Sepolia (84532)
  • Stable Testnet (2201)
  • Arc (1244)
  • Tempo (42431) (Note: Uses token-based fees like PathUSD)

Quick Start: Code Snippets​

The SDK revolves around the ConfidentialTransferClient, which handles the cryptographic heavy lifting.

(Note: We have a separate, dedicated tutorial document on how to build a simple Next.js app with confidential transfers from scratch. The snippets below are for quick reference.)

1. Initialize the Client​

Setup the client with your RPC URL and Chain ID.

import { ConfidentialTransferClient } from '@fairblock/stabletrust';
import { ethers } from 'ethers';

// Example: Base Sepolia setup
const client = new ConfidentialTransferClient(
  'https://sepolia.base.org',
  84532
);

2. Ensure Account is Setup​

Before doing confidential operations, make sure the user account is initialized on-chain.

// signer is a standard ethers.js Signer
const { privateKey, publicKey } = await client.ensureAccount(signer);

3. Deposit Tokens​

Deposit tokens to make the balance confidential. Always parse amounts using the token's decimals (e.g., 6 for USDC).

const tokenDecimals = 6;
const depositAmount = ethers.parseUnits('1.0', tokenDecimals);

await client.confidentialDeposit(signer, tokenAddress, depositAmount);

4. Transfer Confidentially​

Send tokens to any recipient. The amount being transferred will be encrypted and hidden from the public ledger.

const transferAmount = ethers.parseUnits('0.5', tokenDecimals);

await client.confidentialTransfer(
  signer,
  recipientAddress,
  tokenAddress,
  transferAmount
);

5. Check Confidential Balance​

Fetch the user's decrypted available and pending balance. Use the token's decimals to format for UI display.

const balance = await client.getConfidentialBalance(
  signer.address,
  privateKey,
  tokenAddress
);

console.log(
  'Total Confidential Balance:',
  ethers.formatUnits(balance.amount, tokenDecimals)
);