add TLWE ciphertexts addition, substraction, plaintext(constant)-addition

tfhe/src/tlwe.rs

@@ -7,7 +7,7 @@ use std::array;
 use std::iter::Sum;
 use std::ops::{Add, AddAssign, Mul, Sub};
 
-use arith::{Ring, Rq, Tn, Zq, T64, TR};
+use arith::{Ring, Rq, Tn, T64, TR};
 
 const ERR_SIGMA: f64 = 3.2;
 
@@ -36,12 +36,12 @@ impl TLWE {
         Ok((SecretKey(s), pk))
     }
 
-    pub fn encode<const P: u64>(m: Rq<P, 1>) -> Tn<1> {
+    pub fn encode<const P: u64>(m: &Rq<P, 1>) -> Tn<1> {
         let delta = u64::MAX / P; // floored
         let coeffs = m.coeffs();
         Tn(array::from_fn(|i| T64(coeffs[i].0 * delta)))
     }
-    pub fn decode<const P: u64>(p: Tn<1>) -> Rq<P, 1> {
+    pub fn decode<const P: u64>(p: &Tn<1>) -> Rq<P, 1> {
         let p = p.mul_div_round(P, u64::MAX);
         Rq::<P, 1>::from_vec_u64(p.coeffs().iter().map(|c| c.0).collect())
     }
@@ -77,6 +77,63 @@ impl TLWE {
     }
 }
 
+impl<const K: usize> Add<TLWE<K>> for TLWE<K> {
+    type Output = Self;
+    fn add(self, other: Self) -> Self {
+        let a: TR<Tn<1>, K> = self.0 + other.0;
+        let b: Tn<1> = self.1 + other.1;
+        Self(a, b)
+    }
+}
+impl<const K: usize> AddAssign for TLWE<K> {
+    fn add_assign(&mut self, rhs: Self) {
+        for i in 0..K {
+            self.0 .0[i] = self.0 .0[i] + rhs.0 .0[i];
+        }
+        self.1 = self.1 + rhs.1;
+    }
+}
+impl<const K: usize> Sum<TLWE<K>> for TLWE<K> {
+    fn sum<I>(iter: I) -> Self
+    where
+        I: Iterator<Item = Self>,
+    {
+        let mut acc = TLWE::<K>::zero();
+        for e in iter {
+            acc += e;
+        }
+        acc
+    }
+}
+
+impl<const K: usize> Sub<TLWE<K>> for TLWE<K> {
+    type Output = Self;
+    fn sub(self, other: Self) -> Self {
+        let a: TR<Tn<1>, K> = self.0 - other.0;
+        let b: Tn<1> = self.1 - other.1;
+        Self(a, b)
+    }
+}
+
+// plaintext addition
+impl<const K: usize> Add<Tn<1>> for TLWE<K> {
+    type Output = Self;
+    fn add(self, plaintext: Tn<1>) -> Self {
+        let a: TR<Tn<1>, K> = self.0;
+        let b: Tn<1> = self.1 + plaintext;
+        Self(a, b)
+    }
+}
+// plaintext substraction
+impl<const K: usize> Sub<Tn<1>> for TLWE<K> {
+    type Output = Self;
+    fn sub(self, plaintext: Tn<1>) -> Self {
+        let a: TR<Tn<1>, K> = self.0;
+        let b: Tn<1> = self.1 - plaintext;
+        Self(a, b)
+    }
+}
+
 #[cfg(test)]
 mod tests {
     use anyhow::Result;
@@ -86,7 +143,7 @@ mod tests {
 
     #[test]
     fn test_encrypt_decrypt() -> Result<()> {
-        const T: u64 = 32; // plaintext modulus
+        const T: u64 = 128; // msg space (msg modulus)
         const K: usize = 16;
         type S = TLWE<K>;
 
@@ -98,23 +155,84 @@ mod tests {
             let msg_dist = Uniform::new(0_u64, T);
             let m = Rq::<T, 1>::rand_u64(&mut rng, msg_dist)?;
             dbg!(&m);
-            let p: Tn<1> = S::encode::<T>(m);
+            let p: Tn<1> = S::encode::<T>(&m);
             dbg!(&p);
 
             let c = S::encrypt(&mut rng, &pk, &p)?;
             let p_recovered = c.decrypt(&sk);
-            let m_recovered = S::decode::<T>(p_recovered);
+            let m_recovered = S::decode::<T>(&p_recovered);
 
             assert_eq!(m, m_recovered);
 
             // same but using encrypt_s (with sk instead of pk))
             let c = S::encrypt_s(&mut rng, &sk, &p)?;
             let p_recovered = c.decrypt(&sk);
-            let m_recovered = S::decode::<T>(p_recovered);
+            let m_recovered = S::decode::<T>(&p_recovered);
 
             assert_eq!(m, m_recovered);
         }
 
         Ok(())
     }
+
+    #[test]
+    fn test_addition() -> Result<()> {
+        const T: u64 = 128;
+        const K: usize = 16;
+        type S = TLWE<K>;
+
+        let mut rng = rand::thread_rng();
+
+        for _ in 0..200 {
+            let (sk, pk) = S::new_key(&mut rng)?;
+
+            let msg_dist = Uniform::new(0_u64, T);
+            let m1 = Rq::<T, 1>::rand_u64(&mut rng, msg_dist)?;
+            let m2 = Rq::<T, 1>::rand_u64(&mut rng, msg_dist)?;
+            let p1: Tn<1> = S::encode::<T>(&m1); // plaintext
+            let p2: Tn<1> = S::encode::<T>(&m2); // plaintext
+
+            let c1 = S::encrypt(&mut rng, &pk, &p1)?;
+            let c2 = S::encrypt(&mut rng, &pk, &p2)?;
+
+            let c3 = c1 + c2;
+
+            let p3_recovered = c3.decrypt(&sk);
+            let m3_recovered = S::decode::<T>(&p3_recovered);
+
+            assert_eq!((m1 + m2).remodule::<T>(), m3_recovered.remodule::<T>());
+        }
+
+        Ok(())
+    }
+
+    #[test]
+    fn test_add_plaintext() -> Result<()> {
+        const T: u64 = 128;
+        const K: usize = 16;
+        type S = TLWE<K>;
+
+        let mut rng = rand::thread_rng();
+
+        for _ in 0..200 {
+            let (sk, pk) = S::new_key(&mut rng)?;
+
+            let msg_dist = Uniform::new(0_u64, T);
+            let m1 = Rq::<T, 1>::rand_u64(&mut rng, msg_dist)?;
+            let m2 = Rq::<T, 1>::rand_u64(&mut rng, msg_dist)?;
+            let p1: Tn<1> = S::encode::<T>(&m1); // plaintext
+            let p2: Tn<1> = S::encode::<T>(&m2); // plaintext
+
+            let c1 = S::encrypt(&mut rng, &pk, &p1)?;
+
+            let c3 = c1 + p2;
+
+            let p3_recovered = c3.decrypt(&sk);
+            let m3_recovered = S::decode::<T>(&p3_recovered);
+
+            assert_eq!((m1 + m2).remodule::<T>(), m3_recovered);
+        }
+
+        Ok(())
+    }
 }