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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.

Anonymous Transfers​

For applications requiring the highest level of privacy, Stabletrust supports fully anonymous transfers through the Fairycloak relay system.

Standard confidential transfers encrypt transaction amounts while keeping sender and recipient addresses visible onchain. Anonymous transfers go further both the amount and the wallet address are shielded. Transactions are routed through a relay using numeric account IDs entirely decoupled from any public EVM address, making it impossible to link onchain activity back to a specific wallet.

Key properties of anonymous transfers:

  • Amount privacy: Transaction values are encrypted and hidden from public observers.
  • Address privacy: No public EVM address is associated with the transfer accounts are identified by numeric IDs only.
  • Gasless operations: Transfers and withdrawals are relayed by Fairycloak, so users pay no gas for those operations.

Access to anonymous transfers is available to teams building privacy-critical applications. To learn more or request access, reach out to the Fairblock team at hello@fairblock.network.

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 onchain. This initialization is a one-time step per user per 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)
);