From 47948fa1fc6e8fe05b7d19ef06f82f0c51bb39f0 Mon Sep 17 00:00:00 2001
From: Lucas Meier <lucas@cronokirby.com>
Date: Mon, 12 Feb 2024 15:33:59 -0800
Subject: [PATCH] Unify identity treatment across both backends

---
 src/ark_curve/element/projective.rs | 4 ++++
 src/min_curve/element.rs            | 7 +++++++
 2 files changed, 11 insertions(+)

diff --git a/src/ark_curve/element/projective.rs b/src/ark_curve/element/projective.rs
index 0dda93b..de75f83 100644
--- a/src/ark_curve/element/projective.rs
+++ b/src/ark_curve/element/projective.rs
@@ -20,6 +20,10 @@ impl Element {
     pub const GENERATOR: Self = Self {
         inner: EdwardsProjective::new_unchecked(B_X, B_Y, B_T, B_Z),
     };
+
+    pub const IDENTITY: Self = Self {
+        inner: EdwardsProjective::new_unchecked(Fq::ZERO, Fq::ONE, Fq::ZERO, Fq::ONE),
+    };
 }
 
 impl Hash for Element {
diff --git a/src/min_curve/element.rs b/src/min_curve/element.rs
index b6e2fa8..98c0900 100644
--- a/src/min_curve/element.rs
+++ b/src/min_curve/element.rs
@@ -108,6 +108,13 @@ impl Element {
             Element { x, y, z, t }
         }
     }
+    ///
+    /// Convenience method to make identity checks more readable.
+    pub fn is_identity(&self) -> bool {
+        // Section 4.5 of Decaf paper states for cofactor 4 curves we can
+        // just check X = 0 to check equality with identity
+        self.x == Fq::ZERO
+    }
 
     pub fn double(self) -> Self {
         // https://eprint.iacr.org/2008/522 Section 3.3