From 79cabb3d8d7cb61a618046167a91bbb8fd5c2857 Mon Sep 17 00:00:00 2001
From: therealyingtong <yingtong@z.cash>
Date: Fri, 9 Oct 2020 12:21:06 +0800
Subject: [PATCH] Move random scaling of MSM into multiopen verifier

Co-authored-by: Sean Bowe <ewillbefull@gmail.com>
---
 src/poly/multiopen/verifier.rs | 7 ++++++-
 1 file changed, 6 insertions(+), 1 deletion(-)

diff --git a/src/poly/multiopen/verifier.rs b/src/poly/multiopen/verifier.rs
index 36ba1aa..4b1f193 100644
--- a/src/poly/multiopen/verifier.rs
+++ b/src/poly/multiopen/verifier.rs
@@ -25,11 +25,16 @@ impl<'a, C: CurveAffine> Proof<C> {
         transcript: &mut HBase,
         transcript_scalar: &mut HScalar,
         queries: I,
-        msm: MSM<'a, C>,
+        mut msm: MSM<'a, C>,
     ) -> Result<Guard<'a, C>, Error>
     where
         I: IntoIterator<Item = VerifierQuery<'a, C>> + Clone,
     {
+        // Scale the MSM by a random factor to ensure that if the existing MSM
+        // has is_zero() == false then this argument won't be able to interfere
+        // with it to make it true, with high probability.
+        msm.scale(C::Scalar::random());
+
         // Sample x_4 for compressing openings at the same points together
         let x_4: C::Scalar = get_challenge_scalar(Challenge(transcript.squeeze().get_lower_128()));