Types
The TFHE
library provides encrypted integer types and a type system that is checked both at compile time and at run time.
Encrypted integers behave as much as possible as Solidity's integer types. Currently, however, behaviour such as "revert on overflow" is not supported as this would leak some information about the encrypted value. Therefore, arithmetic on e(u)int
types is unchecked, i.e. there is wrap-around on overflow.
Encrypted integers with overflow checking are coming soon to the TFHE
library. They will allow reversal in case of an overflow, but will leak some information about the operands.
In terms of implementation in the fhEVM
, encrypted integers take the form of FHE ciphertexts. The TFHE
library abstracts away that and, instead, exposes ciphertext handles to smart contract developers. The e(u)int
types are wrappers over these handles.
The following encrypted data types are defined:
Higher-precision integers are supported in the TFHE-rs
library and can be added as needed to fhEVM
.
NOTE 1: The
ebool
type is currently implemented as aneuint8
. A more optimized native boolean type will replaceeuint8
.
Verification
When users send serialized ciphertexts as bytes
to the blockchain, they first need to be converted to the respective encrypted integer type. Conversion verifies if the ciphertext is well-formed and includes proof verification. These steps prevent usage of arbitrary inputs. For example, following functions are provided for ebool
, euint8
, euint16
and euint32
:
TFHE.asEbool(bytes ciphertext)
verifies the provided ciphertext and returns anebool
TFHE.asEuint8(bytes ciphertext)
verifies the provided ciphertext and returns aneuint8
TFHE.asEuint16(bytes ciphertext)
verifies the provided ciphertext and returns aneuint16
TFHE.asEuint32(bytes ciphertext)
verifies the provided ciphertext and returns aneuint32
... more functions for the respective encrypted integer types
Example
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