From 42c782a719f60b15fefe1b1e11d36b9b257f4be7 Mon Sep 17 00:00:00 2001
From: kevaundray <kevtheappdev@gmail.com>
Date: Fri, 8 Sep 2023 22:00:11 +0000
Subject: [PATCH] add check for limbs not being less than 2^128

---
 blackbox_solver/src/barretenberg/wasm/mod.rs        |  4 +++-
 blackbox_solver/src/barretenberg/wasm/scalar_mul.rs | 12 ++++++++++++
 2 files changed, 15 insertions(+), 1 deletion(-)

diff --git a/blackbox_solver/src/barretenberg/wasm/mod.rs b/blackbox_solver/src/barretenberg/wasm/mod.rs
index 75ca52de..03d9712d 100644
--- a/blackbox_solver/src/barretenberg/wasm/mod.rs
+++ b/blackbox_solver/src/barretenberg/wasm/mod.rs
@@ -34,8 +34,10 @@ pub(crate) enum FeatureError {
     NoValue,
     #[error("Value expected to be i32")]
     InvalidI32,
-    #[error("Value is not a valid grumpkin scalar")]
+    #[error("Value {scalar_as_hex} is not a valid grumpkin scalar")]
     InvalidGrumpkinScalar { scalar_as_hex: String },
+    #[error("Limb {limb_as_hex} is not less than 2^128")]
+    InvalidGrumpkinScalarLimb { limb_as_hex: String },
     #[error("Could not convert value {value} from i32 to u32")]
     InvalidU32 { value: i32, source: std::num::TryFromIntError },
     #[error("Could not convert value {value} from i32 to usize")]
diff --git a/blackbox_solver/src/barretenberg/wasm/scalar_mul.rs b/blackbox_solver/src/barretenberg/wasm/scalar_mul.rs
index c7a30f7c..cabb189e 100644
--- a/blackbox_solver/src/barretenberg/wasm/scalar_mul.rs
+++ b/blackbox_solver/src/barretenberg/wasm/scalar_mul.rs
@@ -31,6 +31,18 @@ impl ScalarMul for Barretenberg {
         let mut bytes = high_16_bytes.to_vec();
         bytes.extend_from_slice(&low_16_bytes);
 
+        let two_pow_128 = BigUint::from(2u128).pow(128);
+        if BigUint::from_bytes_be(&low_16_bytes) >= two_pow_128 {
+            return Err(Error::FromFeature(FeatureError::InvalidGrumpkinScalarLimb {
+                limb_as_hex: hex::encode(low_16_bytes),
+            }));
+        }
+        if BigUint::from_bytes_be(&high_16_bytes) >= two_pow_128 {
+            return Err(Error::FromFeature(FeatureError::InvalidGrumpkinScalarLimb {
+                limb_as_hex: hex::encode(high_16_bytes),
+            }));
+        }
+
         // Check if this is smaller than the grumpkin modulus
         let grumpkin_integer = BigUint::from_bytes_be(&bytes);
         let grumpkin_modulus = BigUint::from_bytes_be(&[