1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55

#![allow(clippy::upper_case_acronyms)]
//! Noise Propagation Estimator Module
//! * Contains material needed to estimate the growth of the noise when performing homomophic
//!   computation

pub mod cross;
pub mod gsw;
pub mod lwe;
pub mod rlwe;

pub use cross::Cross;
pub use gsw::GSW;
pub use lwe::LWE;
pub use rlwe::RLWE;

/// Computes the variance of the error distribution after the addition of two uncorrelated
/// ciphertexts Arguments
/// * `var_ct1` - noise variance of the first ciphertext
/// * `var_ct2` - noise variance of the second ciphertext
/// Output
/// * the variance of the sum of the first and the second ciphertext
pub fn add_ciphertexts(var_ct1: f64, var_ct2: f64) -> f64 {
    var_ct1 + var_ct2
}

/// Computes the variance of the error distribution after the addition several uncorrelated
/// ciphertexts
/// Argument
/// * `var_cts` - noise variance of the ciphertexts
/// Output
/// * the variance of the sum of the ciphertexts
pub fn add_several_ciphertexts(var_cts: &[f64]) -> f64 {
    let mut res: f64 = 0.;
    for var in var_cts.iter() {
        res += *var;
    }
    res
}

/// Computes the number of bits affected by the noise with a variance var describing a normal
/// distribution takes into account the number of bits of the integers
pub fn nb_bit_from_variance_99(var: f64, torus_bit: usize) -> usize {
    // compute sigma
    let sigma: f64 = f64::sqrt(var);

    // the constant to get 99% of the normal distribution
    let z: f64 = 3.;
    let tmp = torus_bit as f64 + f64::log2(sigma * z);
    if tmp < 0. {
        // means no bits are affected by the noise in the integer representation (discrete space)
        0usize
    } else {
        tmp.ceil() as usize
    }
}