> ## Documentation Index
> Fetch the complete documentation index at: https://docs.sophon.xyz/llms.txt
> Use this file to discover all available pages before exploring further.

# USDC

> Learn about how to use USDC on Sophon

# USDC on Sophon

USDC on Sophon is implemented through a custom bridge implementation that enables seamless transfer of USDC between **Ethereum** (L1) and **Sophon** (L2). This bridge serves as an interim solution until ZKSync completes its interoperability implementation.

## Contract Addresses

* **L2 USDC Token**: [`0x9Aa0F72392B5784Ad86c6f3E899bCc053D00Db4F`](https://explorer.sophon.xyz/address/0x9Aa0F72392B5784Ad86c6f3E899bCc053D00Db4F)
* **L1 USDC Bridge**: [`0xf553E6D903AA43420ED7e3bc2313bE9286A8F987`](https://etherscan.io/address/0xf553E6D903AA43420ED7e3bc2313bE9286A8F987)
* **L2 USDC Bridge**: [`0x0f44bac3ec514be912aa4359017593b35e868d74`](https://explorer.sophon.xyz/address/0x0f44bac3ec514be912aa4359017593b35e868d74)

## Bridging USDC

### L1 → L2 (Ethereum to Sophon)

1. Call `bridgehub.requestL2TransactionTwoBridges` with the custom L1 bridge address as `secondBridgeAddress`
2. The bridgehub contract forwards the call to `customBridgeL1.bridgehubDeposit`
3. USDC is transferred from the user to the bridge contract
4. Sequencers pick up the event and call `customL2Bridge.finalizeDeposit` on L2
5. The L2 bridge mints USDC on Sophon

### L2 → L1 (Sophon to Ethereum)

1. Call `customBridgeL2.withdraw` on Sophon
2. Once the batch is sealed, call `customL1Bridge.finalizeWithdrawal` on Ethereum to complete the withdrawal

## Technical Details

The custom bridge implementation is based on the [Shared Bridge](https://docs.zksync.io/zk-stack/components/shared-bridges) code but modified to support the native [USDC standard](https://github.com/matter-labs/usdc-bridge). The bridge consists of two main contracts:

* `L1USDCBridge.sol`: Handles operations on Ethereum
* `L2USDCBridge.sol`: Handles operations on Sophon

The L2 bridge contract has the MINTER role on the USDC token contract, allowing it to mint USDC tokens on Sophon when deposits are finalized.

## Bridged USDC Standard

The USDC implementation on Sophon follows Circle's [Bridged USDC Standard](https://www.circle.com/bridged-usdc), which provides a secure and standardized way to implement bridged USDC with the possibility of upgrading to native USDC issuance in the future.

### Key Features

* **Standardized Implementation**: The bridged USDC token contract uses Circle's audited FiatToken implementation, the same code that secures billions in USDC liquidity across other chains
* **Upgradability**: The implementation supports in-place upgrades to native USDC, allowing for a seamless transition without requiring time-consuming liquidity migration
* **Security**: Built on open-source, audited ERC-20 contract code that follows Circle's security standards
* **Compatibility**: While bridged USDC is not initially compatible with CCTP (Cross-Chain Transfer Protocol), the upgrade path to native USDC would enable this functionality

### Bridge Requirements

The bridge implementation includes required functionality for potential future upgrades:

1. **Pausable Bridging**: The ability to pause USDC transfers to finalize the token supply
2. **USDC Burning**: Capability to burn locked USDC on the source chain during potential upgrades
3. **Ownership Transfer**: Support for secure transfer of contract ownership to Circle if an upgrade to native USDC is mutually agreed upon

### Role Management

The token contract implements Circle's role-based access control system:

* **Implementation Owner:** Controls assignment of all roles and can be transferred to Circle for native upgrade
* **ProxyAdmin:** Manages proxy upgrades
* **Minter Role:** Assigned to the bridge contract for minting operations