FHE.sol Overview

Encrypted data types, imports, and general usage of the FHE Solidity library

The FHE library provides functions for working with Fully Homomorphic Encryption (FHE) in Solidity smart contracts. It enables computations on encrypted data without decrypting it, ensuring privacy throughout your contract’s execution.

Import

import '@fhenixprotocol/cofhe-contracts/FHE.sol';

All functions are prefixed with FHE. when called. For example: FHE.add(a, b) or FHE.allowPublic(value).

Encrypted Data Types

Type	Description
ebool	Encrypted boolean value
euint8	Encrypted 8-bit unsigned integer
euint16	Encrypted 16-bit unsigned integer
euint32	Encrypted 32-bit unsigned integer
euint64	Encrypted 64-bit unsigned integer
euint128	Encrypted 128-bit unsigned integer
eaddress	Encrypted Ethereum address

Input Types

Each encrypted type has a corresponding input type, used when receiving encrypted data from the client SDK. An input arrives as a handle plus a bytes proof, and FHE.asEuintXX(handle, proof) converts the pair into the encrypted type:

Input Type	Encrypted Type
externalEbool	ebool
externalEuint8	euint8
externalEuint16	euint16
externalEuint32	euint32
externalEuint64	euint64
externalEuint128	euint128
externalEaddress	eaddress

Shared Types

A value handed over by another contract arrives as a shared type instead. FHE.shareEuintXX(value, receiver) produces one, and the receiver unwraps it with FHE.receiveEuintXXParam or FHE.receiveEuintXXFromCall:

Shared Type	Encrypted Type
sharedEbool	ebool
sharedEuint8	euint8
sharedEuint16	euint16
sharedEuint32	euint32
sharedEuint64	euint64
sharedEuint128	euint128
sharedEaddress	eaddress

See inputs for when to use each.

Security Considerations

1. Initialization: All FHE functions check if their inputs are initialized and set them to 0 if not.

2. Decryption: Decryption is a two-phase process. Mark values with allowPublic onchain, decrypt offchain via the Client SDK, then publish/verify the result with publishDecryptResult or verifyDecryptResult. Only reveal values when absolutely necessary.

3. Security Zones: Some functions accept a securityZone parameter to isolate different encrypted computations. FHE operations can only be performed between ciphertexts that share the same security zone.

4. Access Control: The library provides fine-grained access control through the allow* functions. Always set proper permissions before accessing encrypted values.

5. Type Safety: Ensure encrypted values use compatible types when performing operations. Type mismatches will cause errors.