Offramp (USDC to Fiat)

Overview

Convert shielded USDC to fiat currency through the ZKP2P peer-to-peer protocol.

Architecture

• Source: Polkadot network (user sends DOT)
• Bridge: DOT → ETH (gas) and DOT → USDC (for offramp)
• Destination: Base network (for USDC offramp execution)

Flow

Step 1: Bridge DOT → ETH (for gas)

• Users send DOT to a deposit address
• Receive ETH on Base network for transaction fees
• Required if Base ETH balance < $1.5 equivalent

Step 2: Bridge DOT → USDC

• Users send DOT to receive USDC on Base
• Can use existing USDC balance on Base (skips this step)
• Rate estimation via /exchange_rate endpoint

Step 3: Offramp USDC → Fiat

• Approve USDC spending on Base
• Create deposit with platform/payment details
• Order sent to ZKP2P orderbook for P2P fulfillment

Platforms

Supported Fiat Currencies

• ARS (Argentine Peso)
• AUD (Australian Dollar)
• CHF (Swiss Franc)
• EUR (Euro)
• GBP (British Pound)
• MXN (Mexican Peso)
• SGD (Singapore Dollar)
• THB (Thai Baht)
• USD (US Dollar)

Supported Assets

The offramp supports all pallet-assets on Polkadot and Kusama via the ERC20 precompile system.

Asset Precompile Addresses

Pallet assets use the precompile address format: 0x{assetIdHex}00000000000000000000000001200000

Common assets:

• USDC: Asset ID 1 (via precompile on Asset Hub)
• USDT: Asset ID varies by chain
• PSILV: Asset ID 50000867 on Paseo AssetHub

Asset Shielding

Use the @kusamashield/shielded-transfers library to shield assets before offramping:

// Shield PSILV on Paseo
const deposit = await shieldAssetPaseo(50000867, "100", wallet);

// Bridge to Base and offramp
// See integrate_sdk.md for withdrawal flow

Key Addresses

• USDC (Base): 0x833589fCD6eDb6E08f4c7C32D4f71b54bdA02913
• Offramp Contract: 0x777777779d229cdF3110e9de47943791c26300Ef
• Base Chain ID: 8453

Troubleshooting

• Insufficient gas: Bridge DOT → ETH first
• Approval failure: Ensure USDC allowance for offramp contract
• Order expired: Complete within 10 minutes
• Network mismatch: Auto-switches to Base if needed

Video Demo

Watch the full video demo showing the complete offramp flow from DOT bridging to fiat withdrawal.