Debug decrypt

This guide explains how to use the debug.decrypt[XX] functions for debugging encrypted data in mocked environments during development with fhEVM.

Overview

The debug.decrypt[XX] functions allow you to decrypt encrypted handles into plaintext values. This feature is useful for debugging encrypted operations such as transfers, balance checks, and other computations involving FHE-encrypted data.

Key points

• Environment: The debug.decrypt[XX] functions work only in mocked environments (e.g., hardhat network).

• Production limitation: In production, decryption is performed asynchronously via the Gateway and requires an authorized onchain request.

• Encrypted types: The debug.decrypt[XX] functions supports various encrypted types, including integers, booleans, and ebytesXX.

• Bypass ACL authorization: The debug.decrypt[XX] functions allow decryption without ACL authorization, useful for verifying encrypted operations during development and testing.

Supported functions

Integer decryption

Decrypts encrypted integers of different bit-widths (euint4, euint8, ..., euint256).

Boolean decryption

Decrypts encrypted booleans (ebool).

Byte array decryption

Decrypts encrypted byte arrays of various sizes (ebytesXX).

Address decryption

Decrypts encrypted addresses.

Function usage

Example: decrypting encrypted values

import { debug } from "../utils";

// Decrypt a 64-bit encrypted integer
const handle64: bigint = await this.erc20.balanceOf(this.signers.alice);
const plaintextValue: bigint = await debug.decrypt64(handle64);
console.log("Decrypted Balance:", plaintextValue);

For a more complete example, refer to the ConfidentialERC20 test file.

Example: decrypting byte arrays

// Decrypt a 128-byte encrypted value
const ebytes128Handle: bigint = ...; // Get handle for the encrypted bytes
const decryptedBytes: string = await debug.decryptEbytes128(ebytes128Handle);
console.log("Decrypted Bytes:", decryptedBytes);

How it works

Verifying types

Each decryption function includes a type verification step to ensure the provided handle matches the expected encrypted type. If the type is mismatched, an error is thrown.

function verifyType(handle: bigint, expectedType: number) {
  const typeCt = handle >> 8n;
  if (Number(typeCt % 256n) !== expectedType) {
    throw "Wrong encrypted type for the handle";
  }
}

Environment checks

if (network.name !== "hardhat") {
  throw Error("This function can only be called in mocked mode");
}

Best practices

• Use only for debugging: These functions require access to private keys and are meant exclusively for local testing and debugging.

• Production decryption: For production, always use the asynchronous Gateway-based decryption.