What is Concrete-core?
This library contains a set of low-level primitives which can be used to implement Fully Homomorphically Encrypted (FHE) programs. In a nutshell, fully homomorphic encryption makes it possible to perform arbitrary computations over encrypted data. With FHE, you can perform computations without putting your trust in third-party computation providers.


This library is geared towards people who already know their way around FHE. It gives the user freedom of choice over a breadth of parameters, which can lead to less than 128 bits of security if chosen incorrectly.
Fortunately, we propose multiple libraries that are built on top of concrete-core and which propose a safer API. To see which one best suits your needs, see the concrete homepage.


concrete-core is a modular library which makes it possible to use different backends to perform FHE operations. Its design revolves around two modules:
  • The [specification] module contains a specification (in the form of traits) of the concrete FHE scheme. It describes the FHE objects and operators, which are exposed by the library.
  • The [backends] module contains various backends implementing all or a part of this scheme. These different backends can be activated by feature flags, each making use of different hardware or system libraries to make the operations faster. Check the Rust documentation for a full description of supported backends, engines and entities.

Activating backends

The different backends can be activated using the feature flags backend_*. The backend_default contains an engine executing operations on CPUs. It is activated by default.


This crate assumes that the user is comfortable with the theory behind FHE. If you prefer to use a simpler API, that will perform sanity checks on your behalf, the higher-level concrete crate should have your back.


Here is a small example of how one could use concrete-core to perform a simple operation homomorphically:
// This examples shows how to multiply a secret value by a public one homomorphically.
// First we import the proper symbols:
use concrete_core::prelude::Variance;
use concrete_core::prelude::LweDimension;
use concrete_core::prelude::*;
use std::error::Error;
fn main() -> Result<(), Box<dyn Error>> {
let lwe_dimension = LweDimension(750);
let noise = Variance(2_f64.powf(-104.));
// Here a hard-set encoding is applied on the input (shift by 59 bits) which corresponds here
// to a precision of 4 bits with an additional bit of padding (won't be used but required for
// PBS)
let raw_input = 3_u64 << 59;
// We will multiply by 4
let raw_input_cleatext = 4_u64;
// Unix seeder must be given a secret input.
// Here we just give it 0, which is totally unsafe.
const UNSAFE_SECRET: u128 = 0;
let mut engine = DefaultEngine::new(Box::new(UnixSeeder::new(UNSAFE_SECRET)))?;
// We create a cleartext from the raw cleartext
let cleartext: Cleartext64 = engine.create_cleartext_from(&raw_input_cleatext)?;
let key: LweSecretKey64 = engine.generate_new_lwe_secret_key(lwe_dimension)?;
// We crate the input plaintext from the raw input
let input_plaintext = engine.create_plaintext_from(&raw_input)?;
let input_ciphertext = engine.encrypt_lwe_ciphertext(&key, &input_plaintext, noise)?;
// The content of the output ciphertext will be discarded, use a placeholder plaintext of 0
let placeholder_output_plaintext = engine.create_plaintext_from(&0u64)?;
let mut ouptut_ciphertext =
engine.encrypt_lwe_ciphertext(&key, &placeholder_output_plaintext, noise)?;
// Perform the multiplication, overwriting (discarding) the output ciphertext content
&mut ouptut_ciphertext,
// Get the decrypted result as a plaintext and then a raw value
let decrypted_plaintext = engine.decrypt_lwe_ciphertext(&key, &ouptut_ciphertext)?;
let raw_decrypted_plaintext = engine.retrieve_plaintext(&decrypted_plaintext)?;
// Round the output for our 4 bits of precision
let output = raw_decrypted_plaintext >> 58;
let carry = output % 2;
let output = ((output >> 1) + carry) % (1 << 5);
// Check the high bits have the result we expect
assert_eq!(output, 12);



This software is distributed under the BSD-3-Clause-Clear license. If you have any questions, please contact us at [email protected].
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Activating backends