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 with overflow checking will soon be available in the TFHE library. These will allow reversible arithmetic operations but may reveal some information about the input values.

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:

Type	Supported
ebool	Yes
euint4	Yes
euint8	Yes
euint16	Yes
euint32	Yes
euint64	Yes
euint128	Yes
euint256	Yes
eaddress	Yes
ebytes64	Yes
ebytes128	Yes
ebytes256	Yes
eint8	No, coming soon
eint16	No, coming soon
eint32	No, coming soon
eint64	No, coming soon
eint128	No, coming soon
eint256	No, coming soon

Higher-precision integer types are available in the TFHE-rs library and can be added to fhEVM as needed.