Cryptographic parameters

Default parameters

Some cryptographic parameters will require tuning to ensure both the correctness of the result and the security of the computation.

To make it simpler, we've provided two sets of parameters, which ensure correct computations for a certain probability with the standard security of 128 bits. There exists an error probability due to the probabilistic nature of the encryption, which requires adding randomness (noise) following a Gaussian distribution. If this noise is too large, the decryption will not give a correct result. There is a trade-off between efficiency and correctness: generally, using a less efficient parameter set (in terms of computation time) leads to a smaller risk of having an error during homomorphic evaluation.

The following array summarizes this:

User-defined parameters

You can also create your own set of parameters. This is an unsafe operation as failing to properly fix the parameters will result in an incorrect and/or insecure computation:

use tfhe::boolean::prelude::*;

fn main() {
    // WARNING: might be insecure and/or incorrect
    // You can create your own set of parameters
    let parameters = BooleanParameters::new(
        LweDimension(586),
        GlweDimension(2),
        PolynomialSize(512),
        DynamicDistribution::new_gaussian_from_std_dev(
            StandardDev(0.00008976167396834998),
        ),
        DynamicDistribution::new_gaussian_from_std_dev(
            StandardDev(0.00000002989040792967434),
        ),
        DecompositionBaseLog(8),
        DecompositionLevelCount(2),
        DecompositionBaseLog(2),
        DecompositionLevelCount(5),
        EncryptionKeyChoice::Small,
    );
}