fhe

A pure-Rust implementation of fully homomorphic encryption schemes based on Ring-LWE.

This library implements Fully Homomorphic Encryption schemes, i.e., encryption schemes which perform implicit additions and multiplications on plaintext values while exclusively manipulating encrypted data.

This library provides implementations of:

• BFV, the Brakerski-Fan-Vercauteren (BFV) homomorphic encryption scheme. More precisely, this library implements a leveled variant of the HPS (Halevi--Polyakov--Shoup) RNS-variant of the scheme.

Installation

Add the following to your Cargo.toml:

[dependencies]
fhe = "0.1.1"

Example

Below is a simple example using BFV of an homomorphic multiplication. One ciphertext encrypts the value 20 using the secret key, and one ciphertext encrypts the value -7 using the public key. The ciphertexts are then multiplied, and after decryption, the program checks that the decrypted value has 20 * (-7) = -140 in the first coefficient.

use fhe::bfv::{BfvParametersBuilder, Ciphertext, Encoding, Plaintext, PublicKey, SecretKey};
use fhe_traits::*;
use rand::rng;
use std::error::Error;

fn main() -> Result<(), Box<dyn Error>> {
    let parameters = BfvParametersBuilder::new()
            .set_degree(2048)
            .set_moduli(&[0x3fffffff000001])
            .set_plaintext_modulus(1 << 10)
            .build_arc()?;
    let mut rng = rng();
    let secret_key = SecretKey::random(&parameters, &mut rng);
    let public_key = PublicKey::new(&secret_key, &mut rng);

    let plaintext_1 = Plaintext::try_encode(&[20_u64], Encoding::poly(), &parameters)?;
    let plaintext_2 = Plaintext::try_encode(&[-7_i64], Encoding::poly(), &parameters)?;

    let ciphertext_1: Ciphertext = secret_key.try_encrypt(&plaintext_1, &mut rng)?;
    let ciphertext_2: Ciphertext = public_key.try_encrypt(&plaintext_2, &mut rng)?;

    let result = &ciphertext_1 * &ciphertext_2;

    let decrypted_plaintext = secret_key.try_decrypt(&result)?;
    let decrypted_vector = Vec::<i64>::try_decode(&decrypted_plaintext, Encoding::poly())?;

    assert_eq!(decrypted_vector[0], -140);

    Ok(())
}

Note that operations actually happen modulo the plaintext_modulus, here set to 1024 (= 1 << 10); for example, we would have had that the homomorphic multiplication of 805 and -7 is 509 = (805 * (-7)) mod 1024. Additionally, the poly() encoding means that the vector being encoded corresponds to the coefficients of a polynomial in (ZZ / (1024))[x] / (x^2048+1) (and homomorphic multiplication happens in that ring); here since only one coefficient is provided, the value is placed in the constant coefficient. The library also contains a simd() encoding, which enables component-wise operation on the values of the vector, provided the technical limitation that the plaintext modulus is congruent to 1 modulo twice the polynomial degree.

Examples

More examples exercizing multiple functions from the API are provided in the repository examples/. For example, this library implements SealPIR and MulPIR, which can be run as follows:

cargo run --release --example sealpir

and

cargo run --release --example mulpir

Performance

Micro benchmarks can be obtained by running cargo bench. This crate uses criterion.rs for benchmarks.

Unit tests

Run tests with cargo test.

⚠️ Security / Stability

The implementations in this crate have never been independently audited for security.

Use at your own risk.