From 1dac2f53bb8f6edf233a064f17ade13923268c26 Mon Sep 17 00:00:00 2001
From: Henry de Valence <hdevalence@hdevalence.ca>
Date: Wed, 22 Feb 2017 23:06:59 -0800
Subject: [PATCH] Implement Identity for CompressedEdwardsY

---
 src/curve.rs | 15 +++++++++++++++
 src/decaf.rs |  4 +---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/curve.rs b/src/curve.rs
index ec9c093..8130d24 100644
--- a/src/curve.rs
+++ b/src/curve.rs
@@ -218,6 +218,15 @@ pub trait Identity {
     fn identity() -> Self;
 }
 
+impl Identity for CompressedEdwardsY {
+    fn identity() -> CompressedEdwardsY {
+        CompressedEdwardsY([1, 0, 0, 0, 0, 0, 0, 0,
+                            0, 0, 0, 0, 0, 0, 0, 0,
+                            0, 0, 0, 0, 0, 0, 0, 0,
+                            0, 0, 0, 0, 0, 0, 0, 0])
+    }
+}
+
 impl Identity for ExtendedPoint {
     fn identity() -> ExtendedPoint {
         ExtendedPoint{ X: FieldElement::zero(),
@@ -1161,6 +1170,12 @@ mod test {
         assert!(p2.is_small_order() == false);
     }
 
+    #[test]
+    fn test_compressed_identity() {
+        assert_eq!(ExtendedPoint::identity().compress(),
+                   CompressedEdwardsY::identity());
+    }
+
     #[test]
     fn test_is_identity() {
         assert!(ExtendedPoint::identity().is_identity());
diff --git a/src/decaf.rs b/src/decaf.rs
index 2537fbb..93f22e2 100644
--- a/src/decaf.rs
+++ b/src/decaf.rs
@@ -308,9 +308,7 @@ mod test {
     fn test_decaf_decompress_id() {
         let compressed_id = CompressedDecaf::identity();
         let id = compressed_id.decompress().unwrap();
-        // This should compress (as ed25519) to the following:
-        let mut bytes = [0u8; 32]; bytes[0] = 1;
-        assert_eq!(id.0.compress(), CompressedEdwardsY(bytes));
+        assert_eq!(id.0.compress(), CompressedEdwardsY::identity());
     }
 
     #[test]