From 8264e09462ce0e18f6bb01c8df34da716c7bcccc Mon Sep 17 00:00:00 2001
From: Filippo Valsorda <hi@filippo.io>
Date: Sun, 20 Jan 2019 17:30:31 -0500
Subject: [PATCH] First ristretto255 function: EQUALS

---
 ristretto255.go | 33 +++++++++++++++++++++++++++++++++
 1 file changed, 33 insertions(+)
 create mode 100644 ristretto255.go

diff --git a/ristretto255.go b/ristretto255.go
new file mode 100644
index 0000000..1f92c58
--- /dev/null
+++ b/ristretto255.go
@@ -0,0 +1,33 @@
+// Copyright 2016 The Go Authors. All rights reserved.
+// Copyright 2019 George Tankersley. All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+// Package ristretto255 implements the ristretto255 prime-order group as
+// specified in draft-hdevalence-cfrg-ristretto-00.
+package ristretto255
+
+import (
+	"github.com/gtank/ristretto255/internal/edwards25519"
+)
+
+// Element is an element of the ristretto255 prime-order group.
+type Element struct {
+	r edwards25519.ExtendedGroupElement
+}
+
+// Equal returns 1 if e is equivalent to ee, and 0 otherwise.
+// Note that Elements must not be compared in any other way.
+func (e *Element) Equal(ee *Element) int {
+	var f0, f1 edwards25519.FieldElement
+
+	edwards25519.FeMul(&f0, &e.r.X, &ee.r.Y) // x1 * y2
+	edwards25519.FeMul(&f1, &e.r.Y, &ee.r.X) // y1 * x2
+	out := edwards25519.FeEqual(&f0, &f1)
+
+	edwards25519.FeMul(&f0, &e.r.Y, &ee.r.Y) // y1 * y2
+	edwards25519.FeMul(&f1, &e.r.X, &ee.r.X) // x1 * x2
+	out = out | edwards25519.FeEqual(&f0, &f1)
+
+	return out
+}