CoFHE Foundry Starter

A starter template for developing Fully Homomorphic Encryption (FHE) smart contracts using Fhenix CoFHE and Foundry.

Prerequisites

• Foundry (forge, cast, anvil)
• Node.js (v18+) and npm

Quick Start

# Clone the repository
git clone <repo-url>
cd cofhe-foundry-starter

# Install Solidity dependencies
npm install

# Compile contracts
forge build

# Run tests
forge test -vvv

Project Structure

├── src/
│   └── Counter.sol           # Example FHE counter contract
├── test/
│   ├── Counter.t.sol         # Comprehensive Solidity tests
│   └── FHEOperations.t.sol   # FHE operation / input / ACL coverage
├── script/
│   ├── DeployCounter.s.sol   # Deployment script
│   ├── IncrementCounter.s.sol # Increment interaction
│   └── ResetCounter.s.sol    # Reset with encrypted input
├── foundry.toml              # Foundry configuration
├── package.json              # npm dependencies
└── remappings.txt            # Solidity import remappings

How FHE Testing Works

Tests inherit CofheTest from @cofhe/foundry-plugin and call deployMocks() in setUp(), which deploys and wires the whole mock stack. Each user account is a CofheClient — the in-Solidity stand-in for the JS SDK — which encrypts inputs, builds ACPs, and decrypts outputs. No JS SDK needed.

(externalEuint32 handle, bytes memory proof) = bob.createExternalEuint32(2000, address(counter));

vm.prank(bob.account());
counter.reset(handle, proof);

expectPlaintext(counter.count(), uint32(2000));

For the full testing guide covering all helper functions, FHE operations, ACL, ACPs, and patterns, see TESTING.md.

CoFHE 0.7

This starter targets CoFHE 0.7. The headline changes from earlier versions:

Before	Now
function reset(InEuint32 memory value)	function reset(externalEuint32 value, bytes memory proof)
FHE.asEuint32(inValue)	FHE.asEuint32(handle, proof)
one signature per encrypted input	one signature per batch — FHE.asEuint32s(handles, signature)
bare euintXX passed between contracts	sharedEuintXX + FHE.shareEuintXX / FHE.receiveEuintXXParam
Permission / permit_createSelf()	ACP / ACP_createSelf()
decryptForTx_withoutPermit()	decryptForTx_withoutACP()

Encrypted input proofs are now bound to the consuming contract, so the contract address must be passed when creating one. See the 0.7 migration guide.

Deployment

Setup

cp .env.example .env
# Edit .env with your private key and RPC URLs

Deploy to Testnet

# Ethereum Sepolia
npm run deploy:eth-sepolia

# Arbitrum Sepolia
npm run deploy:arb-sepolia

# Base Sepolia
npm run deploy:base-sepolia

Interact with Deployed Contract

# Set the deployed contract address
export COUNTER_ADDRESS=0x...

# Increment the counter
source .env && forge script script/IncrementCounter.s.sol --rpc-url eth-sepolia --broadcast

Resetting the counter takes an encrypted input, so the handle and proof have to be produced off-chain with @cofhe/sdk (0.7.1) and bound to the deployed Counter address:

const [handle, signature] = await client
  .encryptInputs([2000])
  .setConsumingContract(counterAddress)
  .execute();

export CT_HASH=<handle> PROOF=<signature>
source .env && forge script script/ResetCounter.s.sol --rpc-url eth-sepolia --broadcast

Gas Report

npm run test:gas

Dependencies

Package	Purpose
@fhenixprotocol/cofhe-contracts	FHE type definitions and operations (FHE.sol) — 0.2.0
@cofhe/foundry-plugin	CofheTest / CofheClient Foundry test helpers — 0.7.1
@cofhe/mock-contracts	Mock CoFHE contracts for local testing — 0.7.1
@openzeppelin/contracts	Standard contract utilities
forge-std	Foundry standard library (Test, Script, cheatcodes)

Configuration Notes

• EVM Version: cancun — required for MockACL's transient storage (tstore/tload); note that as of 0.7 FHE.allowTransient allowances expire with the transaction (EIP-1153)
• Code Size Limit: 300000 — the mock stack puts test contracts far past the default 24KB limit
• Solidity Version: 0.8.25 — compatible with CoFHE contracts

Resources

• Fhenix Documentation
• Foundry Book
• CoFHE Contracts