From dfc9e7c0b7391e47580fa1f9f24093c8cbb4f5c8 Mon Sep 17 00:00:00 2001
From: Henry de Valence <hdevalence@hdevalence.ca>
Date: Mon, 16 Jul 2018 22:28:22 -0700
Subject: [PATCH] fixup extendedpoint validity check

---
 src/edwards.rs | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/src/edwards.rs b/src/edwards.rs
index df2f8c8..08eff32 100644
--- a/src/edwards.rs
+++ b/src/edwards.rs
@@ -271,9 +271,11 @@ impl Identity for EdwardsPoint {
 // ------------------------------------------------------------------------
 
 impl ValidityCheck for EdwardsPoint {
-    // XXX this should also check that T is correct
     fn is_valid(&self) -> bool {
-        self.to_projective().is_valid()
+        let point_on_curve = self.to_projective().is_valid();
+        let on_segre_image = (&self.X * &self.Y) == (&self.Z * &self.T);
+
+        point_on_curve && on_segre_image
     }
 }