Encryption

Learn how encryption works in the FHEVM SDK.

Encrypted Types

FHEVM supports these encrypted types:

Type	Description	Range
euint8	8-bit unsigned integer	0 to 255
euint16	16-bit unsigned integer	0 to 65,535
euint32	32-bit unsigned integer	0 to 4,294,967,295
euint64	64-bit unsigned integer	0 to 18,446,744,073,709,551,615
euint128	128-bit unsigned integer	Very large numbers
euint256	256-bit unsigned integer	Very large numbers
ebool	Encrypted boolean	true/false
eaddress	Encrypted address	Ethereum address

External Types

For contract inputs, use external* types:

• externalEuint8, externalEuint16, etc.
• externalEbool
• externalEaddress

These require an inputProof parameter.

Automatic Encryption

The SDK automatically encrypts based on ABI:

// Contract function
function confidentialTransfer(
    address to,
    externalEuint64 amount, // Auto-encrypted
    bytes memory inputProof // Auto-generated
) external;

// SDK usage - just provide plaintext
write({
  functionName: 'confidentialTransfer',
  args: [recipientAddress, 100n], // SDK encrypts 100n
});

Manual Encryption

For advanced use cases:

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

function ManualEncryption() {
  const { instance, state } = useFhevmContext();

  const encryptValue = async (value: number) => {
    if (!instance || !state.signer) return;

    const userAddress = await state.signer.getAddress();
    const input = instance.createEncryptedInput(contractAddress, userAddress);

    input.add64(value);

    const encrypted = await input.encrypt();

    return {
      handle: encrypted.handles[0],
      inputProof: encrypted.inputProof,
    };
  };

  return <button onClick={() => encryptValue(100)}>Encrypt</button>;
}

Encryption Process

1. Input Creation: Create encrypted input builder
2. Value Addition: Add values with appropriate methods
3. Encryption: Generate encrypted handles and proof
4. Transmission: Send to smart contract

Best Practices

Choose Appropriate Type

Use the smallest type that fits your data:

// Good - fits in uint8
input.add8(100);

// Bad - unnecessary large type
input.add256(100);

Batch Encryption

Encrypt multiple values together:

const input = instance.createEncryptedInput(contractAddress, userAddress);
input.add64(amount1);
input.add64(amount2);
input.add8(flag);
const encrypted = await input.encrypt();

Notes

Automatic Detection

The SDK automatically detects encrypted types from your ABI and handles encryption transparently.

Type Mismatch

Ensure the encrypted type matches the contract's expected type to avoid errors.