change LWE secret distribution to Error distribution for all parameters

src/bool/keys.rs

@@ -54,7 +54,8 @@ pub struct ClientKey {
 
 mod impl_ck {
     use crate::{
-        random::DefaultSecureRng,
+        parameters::SecretKeyDistribution,
+        random::{DefaultSecureRng, RandomFillGaussian},
         utils::{fill_random_ternary_secret_with_hamming_weight, puncture_p_rng},
     };
 
@@ -76,15 +77,29 @@ mod impl_ck {
             let lwe_seed = puncture_p_rng::<[u8; 32], DefaultSecureRng>(&mut p_rng, 2);
 
             let mut lwe_prng = DefaultSecureRng::new_seeded(lwe_seed);
+
             let mut out = vec![0i32; self.parameters.lwe_n().0];
-            fill_random_ternary_secret_with_hamming_weight(
-                &mut out,
-                self.parameters.lwe_n().0 >> 1,
-                &mut lwe_prng,
-            );
+
+            match self.parameters.lwe_secret_key_dist() {
+                &SecretKeyDistribution::ErrorDistribution => {
+                    RandomFillGaussian::random_fill(&mut lwe_prng, &mut out);
+                }
+                &SecretKeyDistribution::TernaryDistribution => {
+                    fill_random_ternary_secret_with_hamming_weight(
+                        &mut out,
+                        self.parameters.lwe_n().0 >> 1,
+                        &mut lwe_prng,
+                    );
+                }
+            }
             out
         }
         fn sk_rlwe(&self) -> Vec<Self::Element> {
+            assert!(
+                self.parameters.rlwe_secret_key_dist()
+                    == &SecretKeyDistribution::TernaryDistribution
+            );
+
             let mut p_rng = DefaultSecureRng::new_seeded(self.seed);
             let rlwe_seed = puncture_p_rng::<[u8; 32], DefaultSecureRng>(&mut p_rng, 1);
 
@@ -120,6 +135,11 @@ mod impl_ck {
             <Self as SinglePartyClientKey>::sk_rlwe(&self)
         }
         fn sk_u_rlwe(&self) -> Vec<Self::Element> {
+            assert!(
+                self.parameters.rlwe_secret_key_dist()
+                    == &SecretKeyDistribution::TernaryDistribution
+            );
+
             let mut p_rng = DefaultSecureRng::new_seeded(self.seed);
             let rlwe_seed = puncture_p_rng::<[u8; 32], DefaultSecureRng>(&mut p_rng, 3);
 
@@ -1486,7 +1506,7 @@ pub(super) mod tests {
         bool::ClientKey,
         decomposer::NumInfo,
         lwe::decrypt_lwe,
-        parameters::CiphertextModulus,
+        parameters::{CiphertextModulus, I_2P},
         utils::TryConvertFrom1,
         ArithmeticOps, Row,
     };
@@ -1540,4 +1560,11 @@ pub(super) mod tests {
             .unwrap()
             .log2()
     }
+    // #[test]
+    // fn trial() {
+    //     let parameters = I_2P;
+    //     let ck = ClientKey::new(parameters);
+    //     let lwe = ck.sk_lwe();
+    //     dbg!(lwe);
+    // }
 }

src/bool/ni_mp_api.rs

@@ -447,23 +447,26 @@ mod tests {
     use rand::{thread_rng, RngCore};
 
     use crate::{
+        backend::Modulus,
         bool::{
             keys::tests::{ideal_sk_rlwe, measure_noise_lwe},
             BooleanGates,
         },
-        Encoder, Encryptor, KeySwitchWithId, MultiPartyDecryptor,
+        lwe::decrypt_lwe,
+        utils::tests::Stats,
+        ArithmeticOps, Encoder, Encryptor, KeySwitchWithId, MultiPartyDecryptor,
     };
 
     use super::*;
 
     #[test]
     fn non_interactive_mp_bool_nand() {
-        set_parameter_set(ParameterSelector::NonInteractiveLTE4Party);
+        set_parameter_set(ParameterSelector::NonInteractiveLTE2Party);
         let mut seed = [0u8; 32];
         thread_rng().fill_bytes(&mut seed);
         set_common_reference_seed(seed);
 
-        let parties = 3;
+        let parties = 2;
 
         let cks = (0..parties).map(|_| gen_client_key()).collect_vec();
 
@@ -495,6 +498,8 @@ mod tests {
             ct.extract(0)
         };
 
+        let mut stats = Stats::new();
+
         for _ in 0..1000 {
             // let now = std::time::Instant::now();
             let ct_out =
@@ -510,13 +515,17 @@ mod tests {
             let m_expected = m0 ^ m1;
 
             {
-                let noise = measure_noise_lwe(
-                    &ct_out,
-                    parameters.rlwe_q().encode(m_expected),
-                    &ideal_sk_rlwe,
-                    &rlwe_modop,
-                );
-                println!("Noise: {noise}");
+                // let noise = measure_noise_lwe(
+                //     &ct_out,
+                //     parameters.rlwe_q().encode(m_expected),
+                //     &ideal_sk_rlwe,
+                //     &rlwe_modop,
+                // );
+                // println!("Noise: {noise}");
+
+                let noisy_m = decrypt_lwe(&ct_out, &ideal_sk_rlwe, &rlwe_modop);
+                let noise = rlwe_modop.sub(&parameters.rlwe_q().encode(m_expected), &noisy_m);
+                stats.add_more(&vec![parameters.rlwe_q().map_element_to_i64(&noise)]);
             }
 
             assert!(m_out == m_expected, "Expected {m_expected} but got {m_out}");
@@ -527,5 +536,7 @@ mod tests {
             ct1 = ct0;
             ct0 = ct_out;
         }
+
+        println!("Noise std dev log2: {}", stats.std_dev().abs().log2());
     }
 }

src/bool/parameters.rs

@@ -78,6 +78,16 @@ impl SingleDecomposerParams for (DecompostionLogBase, DecompositionCount) {
     }
 }
 
+#[derive(Clone, PartialEq, Debug)]
+pub(crate) enum SecretKeyDistribution {
+    /// Elements of secret key are sample from Gaussian distribitution with
+    /// \sigma = 3.19 and \mu = 0.0
+    ErrorDistribution,
+    /// Elements of secret key are chosen from the set {1,0,-1} with hamming
+    /// weight `floor(N/2)` where `N` is the secret dimension.
+    TernaryDistribution,
+}
+
 #[derive(Clone, PartialEq, Debug)]
 pub(crate) enum ParameterVariant {
     SingleParty,
@@ -86,6 +96,10 @@ pub(crate) enum ParameterVariant {
 }
 #[derive(Clone, PartialEq)]
 pub struct BoolParameters<El> {
+    /// RLWE secret key distribution
+    rlwe_secret_key_dist: SecretKeyDistribution,
+    /// LWE secret key distribtuion
+    lwe_secret_key_dist: SecretKeyDistribution,
     /// RLWE ciphertext modulus Q
     rlwe_q: CiphertextModulus<El>,
     /// LWE ciphertext modulus q (usually referred to as Q_{ks})
@@ -153,6 +167,14 @@ pub struct BoolParameters {
 }
 
 impl<El> BoolParameters<El> {
+    pub(crate) fn rlwe_secret_key_dist(&self) -> &SecretKeyDistribution {
+        &self.rlwe_secret_key_dist
+    }
+
+    pub(crate) fn lwe_secret_key_dist(&self) -> &SecretKeyDistribution {
+        &self.lwe_secret_key_dist
+    }
+
     pub(crate) fn rlwe_q(&self) -> &CiphertextModulus<El> {
         &self.rlwe_q
     }
@@ -502,6 +524,8 @@ where
 }
 
 pub(crate) const MP_BOOL_PARAMS: BoolParameters<u64> = BoolParameters::<u64> {
+    rlwe_secret_key_dist: SecretKeyDistribution::TernaryDistribution,
+    lwe_secret_key_dist: SecretKeyDistribution::ErrorDistribution,
     rlwe_q: CiphertextModulus::new_non_native(1152921504606830593),
     lwe_q: CiphertextModulus::new_non_native(1 << 20),
     br_q: 1 << 11,
@@ -524,6 +548,8 @@ pub(crate) const MP_BOOL_PARAMS: BoolParameters = BoolParameters:: {
 };
 
 pub(crate) const SMALL_MP_BOOL_PARAMS: BoolParameters<u64> = BoolParameters::<u64> {
+    rlwe_secret_key_dist: SecretKeyDistribution::TernaryDistribution,
+    lwe_secret_key_dist: SecretKeyDistribution::ErrorDistribution,
     rlwe_q: CiphertextModulus::new_non_native(36028797018820609),
     lwe_q: CiphertextModulus::new_non_native(1 << 20),
     br_q: 1 << 11,
@@ -546,6 +572,8 @@ pub(crate) const SMALL_MP_BOOL_PARAMS: BoolParameters = BoolParameters::
 };
 
 pub(crate) const I_2P: BoolParameters<u64> = BoolParameters::<u64> {
+    rlwe_secret_key_dist: SecretKeyDistribution::TernaryDistribution,
+    lwe_secret_key_dist: SecretKeyDistribution::ErrorDistribution,
     rlwe_q: CiphertextModulus::new_non_native(18014398509404161),
     lwe_q: CiphertextModulus::new_non_native(1 << 15),
     br_q: 1 << 11,
@@ -568,6 +596,8 @@ pub(crate) const I_2P: BoolParameters = BoolParameters:: {
 };
 
 pub(crate) const NI_2P: BoolParameters<u64> = BoolParameters::<u64> {
+    rlwe_secret_key_dist: SecretKeyDistribution::TernaryDistribution,
+    lwe_secret_key_dist: SecretKeyDistribution::ErrorDistribution,
     rlwe_q: CiphertextModulus::new_non_native(18014398509404161),
     lwe_q: CiphertextModulus::new_non_native(1 << 15),
     br_q: 1 << 11,
@@ -593,6 +623,8 @@ pub(crate) const NI_2P: BoolParameters = BoolParameters:: {
 };
 
 pub(crate) const NI_4P: BoolParameters<u64> = BoolParameters::<u64> {
+    rlwe_secret_key_dist: SecretKeyDistribution::TernaryDistribution,
+    lwe_secret_key_dist: SecretKeyDistribution::ErrorDistribution,
     rlwe_q: CiphertextModulus::new_non_native(18014398509404161),
     lwe_q: CiphertextModulus::new_non_native(1 << 16),
     br_q: 1 << 11,
@@ -619,6 +651,8 @@ pub(crate) const NI_4P: BoolParameters = BoolParameters:: {
 
 #[cfg(test)]
 pub(crate) const SP_TEST_BOOL_PARAMS: BoolParameters<u64> = BoolParameters::<u64> {
+    rlwe_secret_key_dist: SecretKeyDistribution::TernaryDistribution,
+    lwe_secret_key_dist: SecretKeyDistribution::ErrorDistribution,
     rlwe_q: CiphertextModulus::new_non_native(268369921u64),
     lwe_q: CiphertextModulus::new_non_native(1 << 16),
     br_q: 1 << 9,

src/random.rs

@@ -1,7 +1,7 @@
 use std::cell::RefCell;
 
 use itertools::izip;
-use num_traits::{PrimInt, Zero};
+use num_traits::{FromPrimitive, PrimInt, Zero};
 use rand::{distributions::Uniform, Rng, RngCore, SeedableRng};
 use rand_chacha::ChaCha8Rng;
 use rand_distr::{uniform::SampleUniform, Distribution};
@@ -36,6 +36,15 @@ where
     fn random_fill(&mut self, container: &mut M);
 }
 
+pub trait RandomFillGaussian<M>
+where
+    M: ?Sized,
+{
+    /// Fill container with random elements sampled from normal distribtuion
+    /// with \mu = 0.0 and \sigma = 3.19.
+    fn random_fill(&mut self, container: &mut M);
+}
+
 pub trait RandomFillUniformInModulus<M, P>
 where
     M: ?Sized,
@@ -133,6 +142,23 @@ where
     }
 }
 
+impl<T> RandomFillGaussian<[T]> for DefaultSecureRng
+where
+    T: FromPrimitive,
+{
+    fn random_fill(&mut self, container: &mut [T]) {
+        izip!(
+            rand_distr::Normal::new(0.0, 3.19f64)
+                .unwrap()
+                .sample_iter(&mut self.rng),
+            container.iter_mut()
+        )
+        .for_each(|(from, to)| {
+            *to = T::from_f64(from).unwrap();
+        });
+    }
+}
+
 impl<T> RandomFill<[T; 32]> for DefaultSecureRng
 where
     T: PrimInt + SampleUniform,