From 9da24d8afaf0b9443664604d3272dd336cf99c88 Mon Sep 17 00:00:00 2001
From: Isis Lovecruft <isis@torproject.org>
Date: Thu, 5 Oct 2017 02:15:28 +0000
Subject: [PATCH] Add test for Montgomery ladder with a scalar with high bit
 set.

---
 src/montgomery.rs | 13 +++++++++++++
 1 file changed, 13 insertions(+)

diff --git a/src/montgomery.rs b/src/montgomery.rs
index bb6a9ad..37f447a 100644
--- a/src/montgomery.rs
+++ b/src/montgomery.rs
@@ -545,6 +545,19 @@ mod test {
 
         assert_eq!(result.compress(), expected.to_montgomery().compress());
     }
+
+    #[test]
+    #[should_panic(expected = "assertion failed: self[31] <= 127")]
+    fn ladder_matches_scalarmult_with_scalar_high_bit_set() {
+        let mut s: Scalar = Scalar::one();
+
+        s[31] = 255;
+
+        let result: MontgomeryPoint = &BASE_COMPRESSED_MONTGOMERY.decompress() * &s;
+        let expected: ExtendedPoint = &constants::ED25519_BASEPOINT_TABLE * &s;
+
+        assert_eq!(result.compress(), expected.to_montgomery().compress())
+    }
 }
 
 #[cfg(all(test, feature = "bench"))]