Add

Introduction to homomorphic addition on encrypted values. Demonstrates adding two encrypted numbers without decryption, including input handling, addition, and permission management.

To run this example correctly, make sure the files are placed in the following directories:

.sol file → <your-project-root-dir>/contracts/
.ts file → <your-project-root-dir>/test/

This ensures Hardhat can compile and test your contracts as expected.

🔐 FHE API Reference (6 items)

Types: euint8 · externalEuint8

Functions:

FHE.add() - Homomorphic addition: result = a + b (overflow wraps)
FHE.allow() - Grants PERMANENT permission for address to decrypt/use value
FHE.allowThis() - Grants contract permission to operate on ciphertext
FHE.fromExternal() - Validates and converts external encrypted input using inputProof

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

import {FHE, euint8, externalEuint8} from "@fhevm/solidity/lib/FHE.sol";
import {ZamaEthereumConfig} from "@fhevm/solidity/config/ZamaConfig.sol";

/**
 * @notice Introduction to homomorphic addition on encrypted values.
 *         Demonstrates adding two encrypted numbers without decryption, including
 *         input handling, addition, and permission management.

 * @dev Shows the basic FHE operation and permission flow (FHE.add ~100k gas).
 */
contract FHEAdd is ZamaEthereumConfig {
    euint8 private _a;
    euint8 private _b;
    euint8 private _result;

    /// @notice Set the first operand (encrypted)
    function setA(externalEuint8 inputA, bytes calldata inputProof) external {
        _a = FHE.fromExternal(inputA, inputProof);
        FHE.allowThis(_a);
    }

    /// @notice Set the second operand (encrypted)
    function setB(externalEuint8 inputB, bytes calldata inputProof) external {
        _b = FHE.fromExternal(inputB, inputProof);
        FHE.allowThis(_b);
    }

    /// @notice Compute a + b on encrypted values
    /// @dev Contract operates on ciphertexts - never sees actual values!
    function computeAPlusB() external {
        // 🧮 Homomorphic: operates on encrypted data without decrypting
        _result = FHE.add(_a, _b);

        // 🔑 Why both? allowThis = contract can use it, allow = user can decrypt
        FHE.allowThis(_result);
        FHE.allow(_result, msg.sender);
    }

    /// @notice Returns the encrypted result handle
    function result() public view returns (euint8) {
        return _result;
    }
}

import {
  FhevmType,
  HardhatFhevmRuntimeEnvironment,
} from "@fhevm/hardhat-plugin";
import { HardhatEthersSigner } from "@nomicfoundation/hardhat-ethers/signers";
import { expect } from "chai";
import { ethers } from "hardhat";
import * as hre from "hardhat";

import { FHEAdd, FHEAdd__factory } from "../types";

/** Common signers interface */
interface Signers {
  owner: HardhatEthersSigner;
  alice: HardhatEthersSigner;
}

async function deployFixture() {
  // Contracts are deployed using the first signer/account by default
  const factory = (await ethers.getContractFactory(
    "FHEAdd"
  )) as FHEAdd__factory;
  const fheAdd = (await factory.deploy()) as FHEAdd;
  const fheAdd_address = await fheAdd.getAddress();

  return { fheAdd, fheAdd_address };
}

/**
 * FHE Add Tests
 *
 * Tests basic encrypted addition (euint8).
 * Validates multi-user value setting and homomorphic sum computation.
 */
describe("FHEAdd", function () {
  let contract: FHEAdd;
  let contractAddress: string;
  let signers: Signers;
  let bob: HardhatEthersSigner;

  before(async function () {
    // Check whether the tests are running against an FHEVM mock environment
    if (!hre.fhevm.isMock) {
      throw new Error(`This hardhat test suite cannot run on Sepolia Testnet`);
    }

    const ethSigners: HardhatEthersSigner[] = await ethers.getSigners();
    signers = { owner: ethSigners[0], alice: ethSigners[1] };
    bob = ethSigners[2];
  });

  beforeEach(async function () {
    // Deploy a new contract each time we run a new test
    const deployment = await deployFixture();
    contractAddress = deployment.fheAdd_address;
    contract = deployment.fheAdd;
  });

  it("a + b should succeed", async function () {
    const fhevm: HardhatFhevmRuntimeEnvironment = hre.fhevm;

    let tx;

    // Let's compute 80 + 123 = 203
    const a = 80;
    const b = 123;

    // 🔐 Alice encrypts and sets `a` as 80
    const inputA = await fhevm
      .createEncryptedInput(contractAddress, signers.alice.address)
      .add8(a)
      .encrypt();
    tx = await contract
      .connect(signers.alice)
      .setA(inputA.handles[0], inputA.inputProof);
    await tx.wait();

    // 🔐 Alice encrypts and sets `b` as 123
    const inputB = await fhevm
      .createEncryptedInput(contractAddress, signers.alice.address)
      .add8(b)
      .encrypt();
    tx = await contract
      .connect(signers.alice)
      .setB(inputB.handles[0], inputB.inputProof);
    await tx.wait();

    // 🚀 Bob triggers the on-chain computation.
    // In FHEVM, anyone can trigger a computation if they have permission to access the result
    // or if the logic allows it. See `FHEAdd.sol` for permissions logic.
    tx = await contract.connect(bob).computeAPlusB();
    await tx.wait();

    // 🔓 Verification:
    const encryptedAplusB = await contract.result();

    const clearAplusB = await fhevm.userDecryptEuint(
      FhevmType.euint8, // Specify the encrypted type (euint8)
      encryptedAplusB,
      contractAddress,
      bob // Bob decrypts since the result was granted to him
    );

    expect(clearAplusB).to.equal(a + b);
  });
});

PreviousFHE Operations NextArithmetic Operations

Last updated 2 months ago

import { FhevmType, HardhatFhevmRuntimeEnvironment, } from "@fhevm/hardhat-plugin"; import { HardhatEthersSigner } from "@nomicfoundation/hardhat-ethers/signers"; import { expect } from "chai"; import { ethers } from "hardhat"; import * as hre from "hardhat"; import { FHEAdd, FHEAdd__factory } from "../types"; /** Common signers interface */ interface Signers { owner: HardhatEthersSigner; alice: HardhatEthersSigner; } async function deployFixture() { // Contracts are deployed using the first signer/account by default const factory = (await ethers.getContractFactory( "FHEAdd" )) as FHEAdd__factory; const fheAdd = (await factory.deploy()) as FHEAdd; const fheAdd_address = await fheAdd.getAddress(); return { fheAdd, fheAdd_address }; } /** * FHE Add Tests * * Tests basic encrypted addition (euint8). * Validates multi-user value setting and homomorphic sum computation. */ describe("FHEAdd", function () { let contract: FHEAdd; let contractAddress: string; let signers: Signers; let bob: HardhatEthersSigner; before(async function () { // Check whether the tests are running against an FHEVM mock environment if (!hre.fhevm.isMock) { throw new Error(`This hardhat test suite cannot run on Sepolia Testnet`); } const ethSigners: HardhatEthersSigner[] = await ethers.getSigners(); signers = { owner: ethSigners[0], alice: ethSigners[1] }; bob = ethSigners[2]; }); beforeEach(async function () { // Deploy a new contract each time we run a new test const deployment = await deployFixture(); contractAddress = deployment.fheAdd_address; contract = deployment.fheAdd; }); it("a + b should succeed", async function () { const fhevm: HardhatFhevmRuntimeEnvironment = hre.fhevm; let tx; // Let's compute 80 + 123 = 203 const a = 80; const b = 123; // 🔐 Alice encrypts and sets `a` as 80 const inputA = await fhevm .createEncryptedInput(contractAddress, signers.alice.address) .add8(a) .encrypt(); tx = await contract .connect(signers.alice) .setA(inputA.handles[0], inputA.inputProof); await tx.wait(); // 🔐 Alice encrypts and sets `b` as 123 const inputB = await fhevm .createEncryptedInput(contractAddress, signers.alice.address) .add8(b) .encrypt(); tx = await contract .connect(signers.alice) .setB(inputB.handles[0], inputB.inputProof); await tx.wait(); // 🚀 Bob triggers the on-chain computation. // In FHEVM, anyone can trigger a computation if they have permission to access the result // or if the logic allows it. See `FHEAdd.sol` for permissions logic. tx = await contract.connect(bob).computeAPlusB(); await tx.wait(); // 🔓 Verification: const encryptedAplusB = await contract.result(); const clearAplusB = await fhevm.userDecryptEuint( FhevmType.euint8, // Specify the encrypted type (euint8) encryptedAplusB, contractAddress, bob // Bob decrypts since the result was granted to him ); expect(clearAplusB).to.equal(a + b); }); });