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FhevmInstance

The FhevmInstance is the core encryption engine that powers the FHEVM SDK.

Overview​

FhevmInstance provides:

  • Encryption of plaintext values
  • Decryption of encrypted handles
  • Key pair generation
  • EIP-712 signature creation

Creation​

Instances are created automatically by the SDK:

import { createFhevmInstance } from '@fhevm/sdk';

const instance = await createFhevmInstance({
  provider: window.ethereum,
  mockChains: { 31337: 'http://localhost:8545' },
  signal: abortController.signal,
});

Methods​

createEncryptedInput​

Create an encrypted input builder:

const input = instance.createEncryptedInput(contractAddress, userAddress);
input.add64(100);
const encrypted = await input.encrypt();

userDecrypt​

Decrypt encrypted handles:

const results = await instance.userDecrypt(
  [{ handle, contractAddress }],
  privateKey,
  publicKey,
  signature,
  contractAddresses,
  userAddress,
  startTimestamp,
  durationDays
);

const decryptedValue = results[handle];

generateKeypair​

Generate encryption key pair:

const { publicKey, privateKey } = instance.generateKeypair();

createEIP712​

Create EIP-712 typed data for signatures:

const eip712 = instance.createEIP712(
  publicKey,
  contractAddresses,
  startTimestamp,
  durationDays
);

Usage in Hooks​

The SDK hooks automatically use the FhevmInstance:

function MyComponent() {
  const { instance } = useFhevmContext();

  // instance is available for custom operations
  if (instance) {
    // Manual encryption if needed
  }
}

Notes​

Initialization Time

Creating an FhevmInstance can take several seconds as it loads the WASM module.

Caching

The SDK automatically manages instance lifecycle and caching.