# Concrete Core

This crate contains low-level implementations of homomorphic operators used in the
[`concrete`](https://crates.io/crates/concrete) library ([GitHub Repo](https://github.com/zama-ai/concrete)).

## ⚠ Warning ⚠

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.

## Example

Here is a small example of how one could use `concrete-core` to perform a simple operation
homomorphically:

```rust
// 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>> {
    // DISCLAIMER: the parameters used here are only for test purpose, and cannot be considered secure.
    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)?;

    // Create a container for the output, whose content will be discarded during the operation
    let mut output_ciphertext =
        engine.trivially_encrypt_lwe_ciphertext(lwe_dimension.to_lwe_size(), &input_plaintext)?;

    // Perform the multiplication, overwriting (discarding) the output ciphertext content
    engine.discard_mul_lwe_ciphertext_cleartext(
        &mut output_ciphertext,
        &input_ciphertext,
        &cleartext
    )?;

    // Get the decrypted result as a plaintext and then a raw value
    let decrypted_plaintext = engine.decrypt_lwe_ciphertext(&key, &output_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);

    Ok(())
}
```

## Links

- [TFHE](https://eprint.iacr.org/2018/421.pdf)
- [User documentation](https://docs.zama.ai/concrete-core)
- [Concrete-core V1.0.0-alpha release](https://community.zama.ai/t/concrete-core-v1-0-0-alpha/120)
- [Concrete-core V1.0.0-beta release](https://www.zama.ai/post/announcing-concrete-core-v1-0-beta)
- [Concrete-core V1.0.0-gamma release](https://community.zama.ai/t/concrete-core-v1-0-0-gamma-with-gpu-acceleration/234)

## License

This software is distributed under the BSD-3-Clause-Clear license. If you have any questions,
please contact us at `hello@zama.ai`.