fix lwe ciphertext reuse bug

sunscreen_tfhe/src/ops/encryption/lwe_encryption.rs

@@ -44,6 +44,7 @@ where
     params.assert_valid();
 
     let (a, b) = ct.a_b_mut(params);
+    *b = Torus::zero();
 
     for (a_i, d_i) in a.iter_mut().zip(sk.as_slice().iter()) {
         *a_i = uniform_torus::<S>();
@@ -76,7 +77,7 @@ where
 #[cfg(test)]
 mod tests {
 
-    use crate::{high_level::*, PlaintextBits};
+    use crate::{high_level::*, ops::encryption::encode_and_encrypt_lwe_ciphertext, PlaintextBits};
 
     #[test]
     fn can_encrypt_decrypt() {
@@ -91,6 +92,26 @@ mod tests {
         assert_eq!(pt, 4);
     }
 
+    #[test]
+    fn can_reuse_lwe_ciphertext() {
+        let params = TEST_LWE_DEF_1;
+        let bits = PlaintextBits(4);
+
+        let sk = keygen::generate_binary_lwe_sk(&params);
+
+        for _ in 0..10 {
+            let mut ct = encryption::encrypt_lwe_secret(4, &sk, &params, bits);
+            let pt = encryption::decrypt_lwe(&ct, &sk, &params, bits);
+
+            assert_eq!(pt, 4);
+
+            encode_and_encrypt_lwe_ciphertext(&mut ct, &sk, 3, &params, bits);
+
+            assert_eq!(encryption::decrypt_lwe(&ct, &sk, &params, bits), 3);
+
+        }
+    }
+
     #[test]
     fn can_encrypt_decrypt_uniform() {
         let params = TEST_LWE_DEF_1;