From df909da5d87fda01245c564858522c6c57dd8a75 Mon Sep 17 00:00:00 2001
From: Chris Heyes <22148308+hazeycode@users.noreply.github.com>
Date: Sun, 21 May 2023 12:00:48 +0100
Subject: [PATCH] std.crypto: expose Fe isOdd & add basic parity tests for each
 pcurve (#15734)

* std Secp256k1 Scalar: expose Fe isOdd & add basic parity test

* std.crypto: also add Scalar.isOdd convenience fn for p256 and p384 curves
---
 lib/std/crypto/pcurves/p256/scalar.zig      | 5 +++++
 lib/std/crypto/pcurves/p384/scalar.zig      | 5 +++++
 lib/std/crypto/pcurves/secp256k1/scalar.zig | 5 +++++
 lib/std/crypto/pcurves/tests/p256.zig       | 6 ++++++
 lib/std/crypto/pcurves/tests/p384.zig       | 6 ++++++
 lib/std/crypto/pcurves/tests/secp256k1.zig  | 6 ++++++
 6 files changed, 33 insertions(+)

diff --git a/lib/std/crypto/pcurves/p256/scalar.zig b/lib/std/crypto/pcurves/p256/scalar.zig
index 4e88d1fee7..9506a5e57a 100644
--- a/lib/std/crypto/pcurves/p256/scalar.zig
+++ b/lib/std/crypto/pcurves/p256/scalar.zig
@@ -109,6 +109,11 @@ pub const Scalar = struct {
         return n.fe.isZero();
     }
 
+    /// Return true if the scalar is odd.
+    pub fn isOdd(n: Scalar) bool {
+        return n.fe.isOdd();
+    }
+
     /// Return true if a and b are equivalent.
     pub fn equivalent(a: Scalar, b: Scalar) bool {
         return a.fe.equivalent(b.fe);
diff --git a/lib/std/crypto/pcurves/p384/scalar.zig b/lib/std/crypto/pcurves/p384/scalar.zig
index ef257ab7ce..499305bfec 100644
--- a/lib/std/crypto/pcurves/p384/scalar.zig
+++ b/lib/std/crypto/pcurves/p384/scalar.zig
@@ -98,6 +98,11 @@ pub const Scalar = struct {
         return n.fe.isZero();
     }
 
+    /// Return true if the scalar is odd.
+    pub fn isOdd(n: Scalar) bool {
+        return n.fe.isOdd();
+    }
+
     /// Return true if a and b are equivalent.
     pub fn equivalent(a: Scalar, b: Scalar) bool {
         return a.fe.equivalent(b.fe);
diff --git a/lib/std/crypto/pcurves/secp256k1/scalar.zig b/lib/std/crypto/pcurves/secp256k1/scalar.zig
index e0b5e053e3..2a40c9bf96 100644
--- a/lib/std/crypto/pcurves/secp256k1/scalar.zig
+++ b/lib/std/crypto/pcurves/secp256k1/scalar.zig
@@ -109,6 +109,11 @@ pub const Scalar = struct {
         return n.fe.isZero();
     }
 
+    /// Return true if the scalar is odd.
+    pub fn isOdd(n: Scalar) bool {
+        return n.fe.isOdd();
+    }
+
     /// Return true if a and b are equivalent.
     pub fn equivalent(a: Scalar, b: Scalar) bool {
         return a.fe.equivalent(b.fe);
diff --git a/lib/std/crypto/pcurves/tests/p256.zig b/lib/std/crypto/pcurves/tests/p256.zig
index eab69d351e..716f730dc7 100644
--- a/lib/std/crypto/pcurves/tests/p256.zig
+++ b/lib/std/crypto/pcurves/tests/p256.zig
@@ -134,3 +134,9 @@ test "p256 scalar inverse" {
     const inverse = scalar.invert();
     try std.testing.expectEqualSlices(u8, &out, &inverse.toBytes(.Big));
 }
+
+test "p256 scalar parity" {
+    try std.testing.expect(P256.scalar.Scalar.zero.isOdd() == false);
+    try std.testing.expect(P256.scalar.Scalar.one.isOdd());
+    try std.testing.expect(P256.scalar.Scalar.one.dbl().isOdd() == false);
+}
diff --git a/lib/std/crypto/pcurves/tests/p384.zig b/lib/std/crypto/pcurves/tests/p384.zig
index cba1d91a81..1763cfcfa5 100644
--- a/lib/std/crypto/pcurves/tests/p384.zig
+++ b/lib/std/crypto/pcurves/tests/p384.zig
@@ -144,3 +144,9 @@ test "p384 scalar inverse" {
     const sqr = try sq.sqrt();
     try testing.expect(sqr.equivalent(scalar));
 }
+
+test "p384 scalar parity" {
+    try std.testing.expect(P384.scalar.Scalar.zero.isOdd() == false);
+    try std.testing.expect(P384.scalar.Scalar.one.isOdd());
+    try std.testing.expect(P384.scalar.Scalar.one.dbl().isOdd() == false);
+}
diff --git a/lib/std/crypto/pcurves/tests/secp256k1.zig b/lib/std/crypto/pcurves/tests/secp256k1.zig
index 32fca87691..b651f01e04 100644
--- a/lib/std/crypto/pcurves/tests/secp256k1.zig
+++ b/lib/std/crypto/pcurves/tests/secp256k1.zig
@@ -135,3 +135,9 @@ test "secp256k1 scalar inverse" {
     const inverse = scalar.invert();
     try std.testing.expectEqualSlices(u8, &out, &inverse.toBytes(.Big));
 }
+
+test "secp256k1 scalar parity" {
+    try std.testing.expect(Secp256k1.scalar.Scalar.zero.isOdd() == false);
+    try std.testing.expect(Secp256k1.scalar.Scalar.one.isOdd());
+    try std.testing.expect(Secp256k1.scalar.Scalar.one.dbl().isOdd() == false);
+}