From 4a98d904d2f7643707743ef0bbe52250b37619a8 Mon Sep 17 00:00:00 2001
From: Dragos Rotaru <r.dragos0@gmail.com>
Date: Thu, 17 Oct 2024 13:08:57 +0300
Subject: [PATCH] added masking with zero sharing

---
 iris-mpc-cpu/benches/hnsw.rs                    |  2 +-
 iris-mpc-cpu/src/hawkers/galois_store.rs        |  2 +-
 iris-mpc-cpu/src/next_gen_protocol/ng_worker.rs | 15 ++++++++++-----
 3 files changed, 12 insertions(+), 7 deletions(-)

diff --git a/iris-mpc-cpu/benches/hnsw.rs b/iris-mpc-cpu/benches/hnsw.rs
index a721f7e69..b9c6dde05 100644
--- a/iris-mpc-cpu/benches/hnsw.rs
+++ b/iris-mpc-cpu/benches/hnsw.rs
@@ -127,7 +127,7 @@ fn bench_gr_primitives(c: &mut Criterion) {
                     let ds_and_ts = gr_replicated_pairwise_distance(&mut player_session, &pairs)
                         .await
                         .unwrap();
-                    let ds_and_ts = gr_to_rep3(&player_session, ds_and_ts).await.unwrap();
+                    let ds_and_ts = gr_to_rep3(&mut player_session, ds_and_ts).await.unwrap();
                     ng_cross_compare(
                         &mut player_session,
                         ds_and_ts[0].clone(),
diff --git a/iris-mpc-cpu/src/hawkers/galois_store.rs b/iris-mpc-cpu/src/hawkers/galois_store.rs
index b836056b9..85c011353 100644
--- a/iris-mpc-cpu/src/hawkers/galois_store.rs
+++ b/iris-mpc-cpu/src/hawkers/galois_store.rs
@@ -209,7 +209,7 @@ impl VectorStore for LocalNetAby3NgStoreProtocol {
                 let ds_and_ts = gr_replicated_pairwise_distance(&mut player_session, &pairs)
                     .await
                     .unwrap();
-                let ds_and_ts = gr_to_rep3(&player_session, ds_and_ts).await.unwrap();
+                let ds_and_ts = gr_to_rep3(&mut player_session, ds_and_ts).await.unwrap();
                 ng_cross_compare(
                     &mut player_session,
                     ds_and_ts[0].clone(),
diff --git a/iris-mpc-cpu/src/next_gen_protocol/ng_worker.rs b/iris-mpc-cpu/src/next_gen_protocol/ng_worker.rs
index 3fce9f134..8deb9ec3b 100644
--- a/iris-mpc-cpu/src/next_gen_protocol/ng_worker.rs
+++ b/iris-mpc-cpu/src/next_gen_protocol/ng_worker.rs
@@ -345,19 +345,24 @@ pub async fn ng_replicated_is_match(
     Ok(opened.convert())
 }
 
+/// Converts additive sharing (from trick_dot output) to a replicated sharing by
+/// masking it with a zero sharing
 pub async fn gr_to_rep3(
-    session: &Session,
+    session: &mut Session,
     items: Vec<RingElement<u16>>,
 ) -> eyre::Result<Vec<Share<u16>>> {
     let network = session.network().clone();
     let sid = session.session_id();
     let next_party = session.next_identity()?;
 
+    let masked_items: Vec<_> = items
+        .iter()
+        .map(|x| session.prf_as_mut().gen_zero_share() + x)
+        .collect();
     // sending to the next party
-    let shares_a = items.clone();
     network
         .send(
-            NetworkValue::VecRing16(items).to_network(),
+            NetworkValue::VecRing16(masked_items.clone()).to_network(),
             &next_party,
             &sid,
         )
@@ -374,7 +379,7 @@ pub async fn gr_to_rep3(
             _ => Err(eyre!("Error in receiving in gr_to_rep3 operation")),
         }
     }?;
-    let res: Vec<Share<u16>> = shares_a
+    let res: Vec<Share<u16>> = masked_items
         .into_iter()
         .zip(shares_b)
         .map(|(a, b)| Share::new(a, b))
@@ -699,7 +704,7 @@ mod tests {
                     .await
                     .unwrap();
                 let opened_x = open_additive(&player_session, x.clone()).await.unwrap();
-                let x_rep = gr_to_rep3(&player_session, x).await.unwrap();
+                let x_rep = gr_to_rep3(&mut player_session, x).await.unwrap();
                 let opened_x_rep = open_t_many_16(&player_session, x_rep).await.unwrap();
                 (opened_x, opened_x_rep)
             });