Dfns Smart Account

Introduction

This smart contract is heavily inspired from the SafeLite example: https://github.com/5afe/safe-eip7702/blob/main/safe-eip7702-contracts/contracts/experimental/SafeLite.sol It was stripped from all unecessary logic to only keep the batch functionality. It uses no dependency and rely on some assembly code to save gas usage.

After deployment, this contract is intended to be called by the dfns.co WaaS. It will be used for the Fee Sponsor feature: A Dfns user can create 2 wallets:

• Wallet A (sponsor)
• Wallet B (sponsoree)

Wallet A will hold the gas token of the EVM chain (ETH, BNB, ...). Wallet B will hold various tokens (ERC20) but not necessarily the native token of the chain. With the fee sponsor feature, Wallet B will be able to send some tokens without the need of paying the fees, they will be covered by Wallet A.

Execution Steps of a Fee Sponsor Transaction

• Check whether or not Wallet B is pointing to the Dfns Smart Account contract address, using the eth_getCode RPC Method.
  • If Wallet B does not have any code, sign an EIP-7702 Authorization, to make the EOA point to the Dfns Smart Account contract
  • If Wallet B already points to the Dfns Smart Account, do nothing
  • If Wallet B points to a smart contract which is not the Dfns Smart Account, abort the transaction
• Build the transaction for Wallet B based on the intent of the user, and derive the three parameters: to, value, data, bundle it in the userOps data structure and sign it.
• Build a transaction with Wallet A:
  • Transaction type:
    • If an EIP-7702 Authorization was signed, add the Signed Authorization to the transaction: this will be a type 4 transaction
    • If no Authorization was signed, this will be a classic type 2 transaction
  • the to field of the transaction will be the Wallet B address
  • the value field will be 0
  • the data field will be the smart contract call to execute to pass the signed userOps of Step 2 to the handleOps method.
• Broadcast the transaction:
  • Wallet A pays for the fees
  • Wallet B has its intent executed

UserOps encoding

import { concat, solidityPacked } from 'ethers'

const encodeUserOps = (userOps: { to: string, value: BigInt, data: Uint8Array }[]) => {
  return concat(userOps.map((userOp) =>
    solidityPacked(['address', 'uint256', 'uint256', 'bytes'], [userOp.to, userOp.value, BigInt(userOp.data.length), userOp.data])
  ))
}

UserOps signing

import { TypedDataEncoder, keccak256 } from 'ethers'

const types = {
  HandleOps: [
    { name: 'data', type: 'bytes32' },
    { name: 'nonce', type: 'uint256' },
    { name: 'sponsor', type: 'address' }
  ],
}
const sponsor = '0x1234...'
const nonce = await jsonRpcProvider.getStorage(walletBAddress, '0x10ee8db8a0021e326896fcf9b44ce61becefe5f52e3dfd0bb294aee9b73bc000')
const domain = { chainId, verifyingContract: walletBAddress }
const encodedUserOps = encodeUserOps(userOps)
const signedUserOps = keccak256(encodedUserOps)
const message = { data: signedUserOps, nonce, sponsor }
const toSign = TypedDataEncoder.hash(domain, types, message)
const userOpsSignature = sign(toSign) 

handleOps data

import { Signature } from 'ethers'

const { r, yParityAndS } = Signature.from(userOpsSignature)
const handleOpsData = new Interface(['function handleOps( bytes memory userOps, uint256 r, uint256 vs ) public payable']).encodeFunctionData('handleOps', [
  encodedUserOps,
  r,
  yParityAndS,
])

Deployment

It is deployed on the following chains:

Blockchain	Contract Address
Arbitrum One	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Arbitrum Sepolia	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Base	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Base Sepolia	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Berachain	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Berachain Bepolia	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Binance Smart Chain	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Binance Testnet	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Ethereum Mainnet	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Ethereum Hoodi	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Ethereum Sepolia	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Flow EVM	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Flow EVM Testnet	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Optimism	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Optimism Sepolia	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Plasma	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Plasma Testnet	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Polygon	0xcea43594f38316f0e01c161d8dabde0a07a1f512
Polygon Amoy	0xcea43594f38316f0e01c161d8dabde0a07a1f512

Foundry

Foundry is a blazing fast, portable and modular toolkit for Ethereum application development written in Rust.

Foundry consists of:

• Forge: Ethereum testing framework (like Truffle, Hardhat and DappTools).
• Cast: Swiss army knife for interacting with EVM smart contracts, sending transactions and getting chain data.
• Anvil: Local Ethereum node, akin to Ganache, Hardhat Network.
• Chisel: Fast, utilitarian, and verbose solidity REPL.

Documentation

https://book.getfoundry.sh/

Usage

Build

$ forge build

Test

$ forge test

Format

$ forge fmt

Gas Snapshots

$ forge snapshot

Anvil

$ anvil

Deploy

$ forge create script/DfnsSmartAccount.sol:DfnsSmartAccount --rpc-url <your_rpc_url> --private-key <dummy_private_key>

This is a dry run, use a dummy private key as this is not the real deployment. After running the command, forge will output a Transaction with a Json format, copy the "input" field, and use the Dfns API to broadcast the transaction:

POST https://{{customerApiDomain}}/wallets/:walletId/transactions

{
  "kind": "Json",
  "transaction": {
    "data": "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  }
}

./verify-all.sh <contract_address> <etherscan_api_key>

Cast

$ cast <subcommand>

Help

$ forge --help
$ anvil --help
$ cast --help