Supported types

This document introduces the encrypted integer types provided by the TFHE library in fhEVM and explains their usage, including casting, state variable declarations, and type-specific considerations.

Introduction

The TFHE library offers a robust type system with encrypted integer types, enabling secure computations on confidential data in smart contracts. These encrypted types are validated both at compile time and runtime to ensure correctness and security.

Key features of encrypted types

• Encrypted integers function similarly to Solidity’s native integer types, but they operate on Fully Homomorphic Encryption (FHE) ciphertexts.

• Arithmetic operations on e(u)int types are unchecked, meaning they wrap around on overflow. This design choice ensures confidentiality by avoiding the leakage of information through error detection.

• Future versions of the TFHE library will support encrypted integers with overflow checking, but with the trade-off of exposing limited information about the operands.

Encrypted integers in fhEVM are represented as FHE ciphertexts, abstracted using ciphertext handles. These types, prefixed with e (for example, euint64) act as secure wrappers over the ciphertext handles.

List of encrypted types

The TFHE library currently supports the following encrypted types: