1use anyhow::Result;
  2use itertools::zip_eq;
  3use rand::Rng;
  4use std::array;
  5use std::ops::{Add, Mul};
  6
  7use arith::{Ring, Rq, Tn, T64, TR};
  8
  9use crate::tlwe::{PublicKey, SecretKey, TLWE};
 10
 11#[derive(Clone, Debug)]
 12pub struct TLev<const K: usize>(pub(crate) Vec<TLWE<K>>);
 13
 14impl<const K: usize> TLev<K> {
 15    pub fn encode<const T: u64>(m: &Rq<T, 1>) -> T64 {
 16        let coeffs = m.coeffs();
 17        T64(coeffs[0].0) // N=1, so take the only coeff
 18    }
 19    pub fn decode<const T: u64>(p: &T64) -> Rq<T, 1> {
 20        Rq::<T, 1>::from_vec_u64(p.coeffs().iter().map(|c| c.0).collect())
 21    }
 22    pub fn encrypt(
 23        mut rng: impl Rng,
 24        beta: u32,
 25        l: u32,
 26        pk: &PublicKey<K>,
 27        m: &T64,
 28    ) -> Result<Self> {
 29        let tlev: Vec<TLWE<K>> = (1..l + 1)
 30            .map(|i| {
 31                TLWE::<K>::encrypt(&mut rng, pk, &(*m * (u64::MAX / beta.pow(i as u32) as u64)))
 32            })
 33            .collect::<Result<Vec<_>>>()?;
 34
 35        Ok(Self(tlev))
 36    }
 37    pub fn encrypt_s(
 38        mut rng: impl Rng,
 39        _beta: u32, // TODO rm, and make beta=2 always
 40        l: u32,
 41        sk: &SecretKey<K>,
 42        m: &T64,
 43    ) -> Result<Self> {
 44        let tlev: Vec<TLWE<K>> = (1..l as u64 + 1)
 45            .map(|i| {
 46                let aux = if i < 64 {
 47                    *m * (u64::MAX / (1u64 << i))
 48                } else {
 49                    // 1<<64 would overflow, and anyways we're dividing u64::MAX
 50                    // by it, which would be equal to 1
 51                    *m
 52                };
 53                TLWE::<K>::encrypt_s(&mut rng, sk, &aux)
 54            })
 55            .collect::<Result<Vec<_>>>()?;
 56
 57        Ok(Self(tlev))
 58    }
 59
 60    pub fn decrypt(&self, sk: &SecretKey<K>, beta: u32) -> T64 {
 61        let pt = self.0[0].decrypt(sk);
 62        pt.mul_div_round(beta as u64, u64::MAX)
 63    }
 64}
 65// TODO review u64::MAX, since is -1 of the value we actually want
 66
 67impl<const K: usize> TLev<K> {
 68    pub fn iter(&self) -> std::slice::Iter<TLWE<K>> {
 69        self.0.iter()
 70    }
 71}
 72
 73// dot product between a TLev and Vec<T64>, usually Vec<T64> comes from a
 74// decomposition of T64
 75// TLev * Vec<T64> --> TLWE
 76impl<const K: usize> Mul<Vec<T64>> for TLev<K> {
 77    type Output = TLWE<K>;
 78    fn mul(self, v: Vec<T64>) -> Self::Output {
 79        assert_eq!(self.0.len(), v.len());
 80
 81        // l TLWES
 82        let tlwes: Vec<TLWE<K>> = self.0;
 83        let r: TLWE<K> = zip_eq(v, tlwes).map(|(a_d_i, glwe_i)| glwe_i * a_d_i).sum();
 84        r
 85    }
 86}
 87
 88#[cfg(test)]
 89mod tests {
 90    use anyhow::Result;
 91    use rand::distributions::Uniform;
 92
 93    use super::*;
 94
 95    #[test]
 96    fn test_encrypt_decrypt() -> Result<()> {
 97        const T: u64 = 2; // plaintext modulus
 98        const K: usize = 16;
 99        type S = TLev<K>;
100
101        let beta: u32 = 2;
102        let l: u32 = 16;
103
104        let mut rng = rand::thread_rng();
105        let msg_dist = Uniform::new(0_u64, T);
106
107        for _ in 0..200 {
108            let (sk, pk) = TLWE::<K>::new_key(&mut rng)?;
109
110            let m: Rq<T, 1> = Rq::rand_u64(&mut rng, msg_dist)?;
111            let p: T64 = S::encode::<T>(&m); // plaintext
112
113            let c = S::encrypt(&mut rng, beta, l, &pk, &p)?;
114            let p_recovered = c.decrypt(&sk, beta);
115            let m_recovered = S::decode::<T>(&p_recovered);
116
117            assert_eq!(m.remodule::<T>(), m_recovered.remodule::<T>());
118        }
119
120        Ok(())
121    }
122
123    #[test]
124    fn test_tlev_vect64_product() -> Result<()> {
125        const T: u64 = 2; // plaintext modulus
126        const K: usize = 16;
127
128        let beta: u32 = 2;
129        let l: u32 = 16;
130
131        let mut rng = rand::thread_rng();
132        let msg_dist = Uniform::new(0_u64, T);
133
134        for _ in 0..200 {
135            let (sk, pk) = TLWE::<K>::new_key(&mut rng)?;
136
137            let m1: Rq<T, 1> = Rq::rand_u64(&mut rng, msg_dist)?;
138            let m2: Rq<T, 1> = Rq::rand_u64(&mut rng, msg_dist)?;
139            let p1: T64 = TLev::<K>::encode::<T>(&m1);
140            let p2: T64 = TLev::<K>::encode::<T>(&m2);
141
142            let c1 = TLev::<K>::encrypt(&mut rng, beta, l, &pk, &p1)?;
143            let c2 = p2.decompose(beta, l);
144
145            let c3 = c1 * c2;
146
147            let p_recovered = c3.decrypt(&sk);
148            let m_recovered = TLev::<K>::decode::<T>(&p_recovered);
149
150            assert_eq!((m1.to_r() * m2.to_r()).to_rq::<T>(), m_recovered);
151        }
152
153        Ok(())
154    }
155}