Specification

RemoteHop

Purpose: User wants to move [(s)frxUSD, (s)frxETH, FXS, FPI] from chain A to chain B via LZ.

1. User sends OFT to RemoteHop on Chain A
   • If Chain B == Fraxtal
     1. Chain A RemoteHop sends OFT to recipient on Fraxtal
   • If Chain B != Fraxtal
     1. Chain A RemoteHop sends OFT to Fraxtal Remotehop
     2. Fraxtal Remotehop sends OFT to recipient on chain B.

How to use

Interfaces

interface IERC20 {
    function approve(address spender, uint256 amount) external;
}
interface IOFT {
    function token() external view returns (address);
}

interface IRemoteHop {
        function quote(
        address _oft,
        uint32 _dstEid,
        bytes32 _recipient,
        uint256 _amountLD,
        uint128 _dstGas,
        bytes memory _data
    ) external view returns (uint256 fee);
    function sendOFT(
        address _oft,
        uint32 _dstEid,
        bytes32 _recipient,
        uint256 _amountLD,
        uint128 _dstGas,
        bytes memory _data
    ) external payable;
}

// Ethereum WFRAX => (Fraxtal) => Arbitrum WFRAX

// OFT address found @ https://docs.frax.com/protocol/crosschain/addresses
address remoteHop = 0xFd3B410b82a00B2651b42A13837204c5e3D92e27; // See deployed contracts below
address oft = 0x04ACaF8D2865c0714F79da09645C13FD2888977f; // WFRAX OFT
uint32 dstEid = 30110; // Arbitrum
bytes32 recipient = bytes32(uint256(uint160(0xb0E1650A9760e0f383174af042091fc544b8356f))); // example
uint256 amountLD = 1e18;
uint128 dstGas = 0;
bytes memory data = "";

// 1. Quote cost of send
uint256 fee = IRemoteHop(remoteHop).quote(oft, dstEid, recipient, amountLD, dstGas, data);

// 2. Approve OFT underlying token to be transferred to the remoteHop 
IERC20(IOFT(oft).token()).approve(remoteHop, amountLD);

// 3. Send the OFT to destination
IRemoteHop(remoteHop).sendOFT{value: fee}(oft, dstEid, recipient, amountLD, dstGas, data);

When sending _data, the _recipient on _dstEid must support the interface to receive the tokens via lzCompose():

function hopCompose(
    uint32 _srcEid,
    bytes32 _sender,
    address _oft,
    uint256 _amount,
    bytes memory _data
)

RemoteVaultHop

The RemoteVaultHop system enables users to deposit into and redeem from ERC-4626 vaults on remote chains using cross-chain token hops.

Architecture

1. RemoteVaultHop Contract

• Core orchestrator implementing IHopComposer to handle vault operations across chains
• Manages both local vaults (on the same chain) and remote vaults (on other chains)
• Tracks user deposits via synthetic RemoteVaultDeposit ERC20 tokens

2. RemoteVaultDeposit Contract

• ERC20 receipt token representing user deposits in remote vaults
• Tracks price-per-share with linear interpolation over 100 blocks for smooth price updates
• Provides convenience methods: deposit() and redeem() forward calls to RemoteVaultHop
• Users interact with this token to manage their remote vault positions

Cross-Chain Vault Operations

Deposit Flow (Chain A → Vault on Chain B):

1. User calls RemoteVaultDeposit.deposit(_amount) on Chain A
2. Transfers tokens to RemoteVaultHop and calls HOP.sendOFT() with Action.Deposit message
3. RemoteVaultHop on Chain B receives via hopCompose(), calls vault.deposit()
4. Chain B sends Action.DepositReturn message back with shares received + vault price-per-share
5. Chain A receives return message, mints RemoteVaultDeposit tokens to user, updates price

Redeem Flow (Chain A ← Vault on Chain B):

1. User calls RemoteVaultDeposit.redeem(_amount) on Chain A (burns deposit tokens)
2. Sends Action.Redeem message to Chain B
3. Chain B calls vault.redeem(), sends tokens back with Action.RedeemReturn message
4. Chain A receives underlying tokens, transfers to user

Security:

• Only RemoteVaultHop can mint/burn RemoteVaultDeposit tokens
• Validates incoming messages are from registered RemoteVaultHops

Deployed Contracts

HopV2 Mainnet

Chain	Hop	RemoteAdmin
Fraxtal	0xe8Cd13de17CeC6FCd9dD5E0a1465Da240f951536	0xDC3369C18Ff9C077B803C98b6260a186aDE9A426
Arbitrum	0xf307Ad241E1035062Ed11F444740f108B8D036a6	0x03047fA366900b4cBf5E8F9FEEce97553f20370e
Base	0x22beDD55A0D29Eb31e75C70F54fADa7Ca94339B9	0xF333d66C7e47053b96bC153Bfdfaa05c8BEe7307
Ethereum	0xFd3B410b82a00B2651b42A13837204c5e3D92e27	0xa2db46c06e0B643A926ef60d1fEB744A7385a593