Configuration

This document explains how to enable encrypted computations in your smart contract by setting up the fhEVM environment. Learn how to integrate essential libraries, configure encryption, and add secure computation logic to your contracts.

Core configuration setup

To utilize encrypted computations in Solidity contracts, you must configure the TFHE library and Gateway addresses. The fhevm package simplifies this process with prebuilt configuration contracts, allowing you to focus on developing your contract’s logic without handling the underlying cryptographic setup.

Key components configured automatically

1. TFHE library: Sets up encryption parameters and cryptographic keys.

2. Gateway: Manages secure cryptographic operations, including reencryption and decryption.

3. Network-specific settings: Adapts to local testing, testnets (Sepolia for example), or mainnet deployment.

By inheriting these configuration contracts, you ensure seamless initialization and functionality across environments.

ZamaFHEVMConfig.sol

This configuration contract initializes the fhEVM environment with required encryption parameters.

Import based on your environment:

// For Ethereum Sepolia
import { SepoliaZamaFHEVMConfig } from "fhevm/config/ZamaFHEVMConfig.sol";

Purpose:

• Sets encryption parameters such as cryptographic keys and supported ciphertext types.

• Ensures proper initialization of the FHEVM environment.

Example: using Sepolia configuration

// SPDX-License-Identifier: BSD-3-Clause-Clear
pragma solidity ^0.8.24;

import { SepoliaZamaFHEVMConfig } from "fhevm/config/ZamaFHEVMConfig.sol";

contract MyERC20 is SepoliaZamaFHEVMConfig {
  constructor() {
    // Additional initialization logic if needed
  }
}

ZamaGatewayConfig.sol

To perform decryption or reencryption, your contract must interact with the Gateway, which acts as a secure bridge between the blockchain, coprocessor, and Key Management System (KMS).

Import based on your environment

// For Ethereum Sepolia
import { SepoliaZamaGatewayConfig } from "fhevm/config/ZamaGatewayConfig.sol";

Purpose

• Configures the Gateway for secure cryptographic operations.

• Facilitates reencryption and decryption requests.

Example: Configuring the gateway with Sepolia settings

import "fhevm/lib/TFHE.sol";
import { SepoliaZamaFHEVMConfig } from "fhevm/config/ZamaFHEVMConfig.sol";
import { SepoliaZamaGatewayConfig } from "fhevm/config/ZamaGatewayConfig.sol";
import "fhevm/gateway/GatewayCaller.sol";

contract Test is SepoliaZamaFHEVMConfig, SepoliaZamaGatewayConfig, GatewayCaller {
  constructor() {
    // Gateway and FHEVM environment initialized automatically
  }
}

Using isInitialized

The isInitialized utility function checks whether an encrypted variable has been properly initialized, preventing unexpected behavior due to uninitialized values.

Function signature

function isInitialized(T v) internal pure returns (bool)

Purpose

• Ensures encrypted variables are initialized before use.

• Prevents potential logic errors in contract execution.

Example: Initialization Check for Encrypted Counter

require(TFHE.isInitialized(counter), "Counter not initialized!");

Summary

By leveraging prebuilt configuration contracts like ZamaFHEVMConfig.sol and ZamaGatewayConfig.sol, you can efficiently set up your smart contract for encrypted computations. These tools abstract the complexity of cryptographic initialization, allowing you to focus on building secure, confidential smart contracts.