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Accept fully confidential payments using the MPP SDK on SKALE chains with Programmable Privacy. Confidential tokens (eUSDC) provide native privacy — hiding sender, receiver, and amount onchain.

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Prerequisites

  • Node.js, Bun, or pnpm installed
  • SKALE chain with Programmable Privacy access (SKALE Base Sepolia)
  • eUSDC tokens for testing
  • Understanding of confidential tokens vs standard tokens

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Overview

Confidential token features:
  • Native privacy – Amounts hidden by default at the token level
  • Optional encryption – Add threshold encryption for extra security
  • Gasless support – EIP-3009 for gas-free UX
  • Chains with Programmable Privacy only – Requires a privacy-enabled chain

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Environment Setup

Create a .env file: 
# SKALE Base Sepolia RPC
SKALE_RPC=https://base-sepolia-testnet.skalenodes.com/v1/jubilant-horrible-ancha

# Your receiving address
RECEIVING_ADDRESS=0xYourReceivingAddress

# Chain configuration
CHAIN=skale-base-sepolia
CURRENCY=eUSDC

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Confidential Token Payment

Basic confidential payment with eUSDC: 
import { mpp } from '@skalenetwork/mpp/client'
import { createWalletClient, http } from 'viem'
import { privateKeyToAccount } from 'viem/accounts'

// Setup wallet
const account = privateKeyToAccount('0xYourPrivateKey')
const walletClient = createWalletClient({
  account,
  transport: http(process.env.SKALE_RPC)
})

// Create confidential payment method
const confidentialPayment = mpp.charge({
  chain: 'skale-base-sepolia',
  currency: 'eUSDC',
  extensions: {
    skale: { confidentialToken: true }
  }
})

async function processConfidentialPayment(amount: string) {
  const tx = await confidentialPayment.createTransfer({
    to: process.env.RECEIVING_ADDRESS,
    amount: amount, // Amount in base units
    from: account.address
  })
  
  const hash = await walletClient.sendTransaction(tx)
  console.log('Confidential payment sent:', hash)
  return hash
}

// Process 5 eUSDC privately
await processConfidentialPayment('5000000')

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Gasless Confidential Payments

Combine gasless UX with full privacy: 
const gaslessConfidential = mpp.charge({
  chain: 'skale-base-sepolia',
  currency: 'eUSDC',
  extensions: {
    skale: { confidentialToken: true },
    gasless: 'eip3009'
  }
})

async function processPrivateGaslessPayment(amount: string) {
  const tx = await gaslessConfidential.createTransfer({
    to: process.env.RECEIVING_ADDRESS,
    amount: amount,
    from: account.address
  })
  
  const hash = await walletClient.sendTransaction(tx)
  console.log('Private gasless payment:', hash)
  return hash
}

​
Maximum Privacy (All Features)

Enable all privacy layers: 
const fullPrivacy = mpp.charge({
  chain: 'skale-base-sepolia',
  currency: 'eUSDC',
  extensions: {
    skale: { 
      encrypted: true,      // Threshold encryption
      confidentialToken: true // Native token privacy
    },
    gasless: 'eip3009'        // No gas needed
  }
})

async function processMaximumPrivacy(amount: string) {
  const tx = await fullPrivacy.createTransfer({
    to: process.env.RECEIVING_ADDRESS,
    amount: amount,
    from: account.address
  })
  
  const hash = await walletClient.sendTransaction(tx)
  console.log('Maximum privacy payment:', hash)
  return hash
}

​
Server Integration

Backend processing for confidential payments: 
import { mpp } from '@skalenetwork/mpp/server'
import express from 'express'

const app = express()

const confidentialMethod = mpp.charge({
  chain: 'skale-base-sepolia',
  currency: 'eUSDC',
  extensions: {
    skale: { confidentialToken: true },
    gasless: 'eip3009'
  }
})

app.post('/api/private-payment', async (req, res) => {
  const { amount, from, proof } = req.body
  
  try {
    // Verify proof (confidential token specific)
    const isValid = await verifyConfidentialProof(proof)
    if (!isValid) throw new Error('Invalid proof')
    
    const tx = await confidentialMethod.createTransfer({
      to: process.env.RECEIVING_ADDRESS,
      amount,
      from
    })
    
    res.json({ success: true, txData: tx })
  } catch (error) {
    res.status(400).json({ error: error.message })
  }
})

​
Payment Verification

Verifying confidential transactions: 
import { createPublicClient, http } from 'viem'

const publicClient = createPublicClient({
  transport: http(process.env.SKALE_RPC)
})

async function verifyConfidentialPayment(txHash: string) {
  const receipt = await publicClient.getTransactionReceipt({ hash: txHash })
  
  if (receipt.status !== 'success') {
    throw new Error('Transaction failed')
  }
  
  // Confidential tokens emit different events
  // Check for confidential transfer events
  const confidentialEvents = receipt.logs.filter(
    log => log.topics[0] === '0xConfidentialTransferTopic'
  )
  
  console.log('Confidential payment verified')
  return { verified: true, events: confidentialEvents }
}

​
Testing on SKALE Base Sepolia

SKALE Base Sepolia supports confidential tokens for testing: 
SKALE_RPC=https://base-sepolia-testnet.skalenodes.com/v1/jubilant-horrible-ancha
CHAIN=skale-base-sepolia
CURRENCY=eUSDC

const testConfidential = mpp.charge({
  chain: 'skale-base-sepolia',
  currency: 'eUSDC',
  extensions: {
    skale: { confidentialToken: true },
    gasless: 'eip3009'
  }
})

const tx = await testConfidential.createTransfer({
  to: '0xTestReceiver',
  amount: '100000', // 0.1 eUSDC
  from: account.address
})

​
Comparing Payment Types

FeatureStandardGaslessEncryptedConfidential
ChainSKALE BaseSKALE BaseSKALE BaseSKALE Base Sepolia
TokenUSDC.eUSDC.eUSDC.eeUSDC
Gas tokenCREDIT requiredNot neededCREDIT requiredNot needed (gasless)
Amount visible✓✓HiddenHidden
Native privacy---✓

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Error Handling

try {
  const hash = await processConfidentialPayment('1000000')
} catch (error) {
  if (error.message.includes('BITE')) {
    console.error('Not on a chain with Programmable Privacy')
  } else if (error.message.includes('confidential')) {
    console.error('Token not configured for confidentiality')
  } else if (error.message.includes('eUSDC')) {
    console.error('Insufficient eUSDC balance')
  }
}

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Best Practices

When to use confidential tokens:
  • Maximum privacy requirements
  • Sensitive transaction amounts
  • Chains with Programmable Privacy available
  • Users comfortable with eUSDC
Important considerations:
  • Confidential tokens only work on chains with Programmable Privacy
  • eUSDC is different from USDC.e (different addresses)
  • Always test on SKALE Base Sepolia first
  • Verify chain supports Programmable Privacy before deploying

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