From 8024753be00dd6cb588db3da5a5a963d5c6f2ff2 Mon Sep 17 00:00:00 2001
From: Nicolas Sarlin <nicolas.sarlin@zama.ai>
Date: Wed, 11 Jun 2025 15:16:29 +0200
Subject: [PATCH] fix(zk): test failed with trivial ct equal to 0

---
 tfhe-zk-pok/src/proofs/pke.rs    | 6 ++++--
 tfhe-zk-pok/src/proofs/pke_v2.rs | 6 ++++--
 2 files changed, 8 insertions(+), 4 deletions(-)

diff --git a/tfhe-zk-pok/src/proofs/pke.rs b/tfhe-zk-pok/src/proofs/pke.rs
index 18c87f8d3..5f4a82998 100644
--- a/tfhe-zk-pok/src/proofs/pke.rs
+++ b/tfhe-zk-pok/src/proofs/pke.rs
@@ -1825,7 +1825,9 @@ mod tests {
             (q / t as i128) as u64
         };
 
-        let trivial = rng.gen::<u64>() % effective_cleartext_t;
+        // If trivial is 0 the ct is not modified so the proof will be accepted
+        let trivial = rng.gen_range(1..effective_cleartext_t);
+
         let trivial_pt = trivial * delta;
         let c2_plus_trivial = vec![ct.c2[0].wrapping_add(trivial_pt as i64)];
 
@@ -1871,7 +1873,7 @@ mod tests {
             ct_plus_trivial.c2.clone(),
             testcase.r.clone(),
             testcase.e1.clone(),
-            testcase.m.clone(),
+            m_plus_trivial,
             testcase.e2.clone(),
             &crs,
         );
diff --git a/tfhe-zk-pok/src/proofs/pke_v2.rs b/tfhe-zk-pok/src/proofs/pke_v2.rs
index 37f8842f5..c75f8d72a 100644
--- a/tfhe-zk-pok/src/proofs/pke_v2.rs
+++ b/tfhe-zk-pok/src/proofs/pke_v2.rs
@@ -3180,7 +3180,9 @@ mod tests {
             (q / t as i128) as u64
         };
 
-        let trivial = rng.gen::<u64>() % effective_cleartext_t;
+        // If trivial is 0 the ct is not modified so the proof will be accepted
+        let trivial = rng.gen_range(1..effective_cleartext_t);
+
         let trivial_pt = trivial * delta;
         let c2_plus_trivial = vec![ct.c2[0].wrapping_add(trivial_pt as i64)];
 
@@ -3226,7 +3228,7 @@ mod tests {
             ct_plus_trivial.c2.clone(),
             testcase.r.clone(),
             testcase.e1.clone(),
-            testcase.m.clone(),
+            m_plus_trivial,
             testcase.e2.clone(),
             &crs,
         );