FHE Operations Cheat Sheet

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import { FHE, euint32, euint64, ebool, eaddress } from "@fhevm/solidity/lib/FHE.sol";
import { ZamaEthereumConfig } from "@fhevm/solidity/config/ZamaConfig.sol";

contract MyContract is ZamaEthereumConfig {
    // Your encrypted contract logic here
}

function receiveInput(externalEuint32 encInput, bytes calldata inputProof) external {
    euint32 value = FHE.fromExternal(encInput, inputProof);
    // Now 'value' can be used in FHE operations
    FHE.allowThis(value);
}

euint32 encryptedFive = FHE.asEuint32(5);
ebool encryptedTrue = FHE.asEbool(true);
eaddress encAddr = FHE.asEaddress(msg.sender);

euint8 small = FHE.asEuint8(42);
euint32 bigger = FHE.asEuint32(small);   // Upcast: euint8 -> euint32
euint8 back = FHE.asEuint8(bigger);      // Downcast: euint32 -> euint8 (may truncate)

ebool result = FHE.and(cond1, cond2);   // logical AND
ebool result = FHE.or(cond1, cond2);    // logical OR
ebool result = FHE.not(cond1);          // logical NOT

// FHE.select(condition, valueIfTrue, valueIfFalse)
euint32 result = FHE.select(isGreater, largeValue, smallValue);

// Encrypted equivalent of: if (a) x; else if (b) y; else z;
euint32 result = FHE.select(condA, x, FHE.select(condB, y, z));

// Random number from 0 to 99
euint32 dice = FHE.randEuint32(100);
FHE.allowThis(dice);

// After ANY operation that produces a new ciphertext:
euint32 newBalance = FHE.add(balance, amount);
FHE.allowThis(newBalance);           // Contract can use it in future txs
FHE.allow(newBalance, owner);        // Owner can view/decrypt it

// Return the encrypted handle -- client decrypts via instance.userDecrypt()
function viewMyBalance() external view returns (euint64) {
    return balances[msg.sender]; // ACL must have been set via FHE.allow(balance, msg.sender)
}

// Step 1: Make a value publicly decryptable
FHE.makePubliclyDecryptable(encryptedValue);

// Step 2: Check if a value has been marked for public decryption
bool canDecrypt = FHE.isPubliclyDecryptable(encryptedValue);

// SPDX-License-Identifier: MIT
pragma solidity ^0.8.24;

import { FHE, euint64, ebool } from "@fhevm/solidity/lib/FHE.sol";
import { ZamaEthereumConfig } from "@fhevm/solidity/config/ZamaConfig.sol";

contract ConfidentialToken is ZamaEthereumConfig {
    mapping(address => euint64) private balances;

    function transfer(address to, externalEuint64 encAmount, bytes calldata inputProof) external {
        euint64 amount = FHE.fromExternal(encAmount, inputProof);

        // Encrypted balance check
        ebool hasEnough = FHE.ge(balances[msg.sender], amount);

        // Conditional update (silent fail if insufficient)
        euint64 newSenderBal = FHE.select(
            hasEnough,
            FHE.sub(balances[msg.sender], amount),
            balances[msg.sender]
        );
        euint64 newReceiverBal = FHE.select(
            hasEnough,
            FHE.add(balances[to], amount),
            balances[to]
        );

        // Update storage
        balances[msg.sender] = newSenderBal;
        balances[to] = newReceiverBal;

        // ACL: allow contract + owners
        FHE.allowThis(newSenderBal);
        FHE.allow(newSenderBal, msg.sender);
        FHE.allowThis(newReceiverBal);
        FHE.allow(newReceiverBal, to);
    }
}