From fb89b61cdc2ccf6bda9f77f72315e01fa4ffb7d7 Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Ula=C5=9F=20Erdo=C4=9Fan?= <uerdogan2001@hotmail.com>
Date: Mon, 8 May 2023 04:11:54 +0300
Subject: [PATCH] crypto/secp2561r1: add secp256r1 curve verifiers

---
 crypto/secp256r1/publickey.go | 21 +++++++++++++++++++
 crypto/secp256r1/verifier.go  | 39 +++++++++++++++++++++++++++++++++++
 2 files changed, 60 insertions(+)
 create mode 100644 crypto/secp256r1/publickey.go
 create mode 100644 crypto/secp256r1/verifier.go

diff --git a/crypto/secp256r1/publickey.go b/crypto/secp256r1/publickey.go
new file mode 100644
index 0000000000..c92afaa1e0
--- /dev/null
+++ b/crypto/secp256r1/publickey.go
@@ -0,0 +1,21 @@
+package secp256r1
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"math/big"
+)
+
+// Generates approptiate public key format from given coordinates
+func newPublicKey(x, y *big.Int) *ecdsa.PublicKey {
+	// Check if the given coordinates are valid
+	if x == nil || y == nil || !elliptic.P256().IsOnCurve(x, y) {
+		return nil
+	}
+
+	return &ecdsa.PublicKey{
+		Curve: elliptic.P256(),
+		X:     x,
+		Y:     y,
+	}
+}
diff --git a/crypto/secp256r1/verifier.go b/crypto/secp256r1/verifier.go
new file mode 100644
index 0000000000..67a0dd787d
--- /dev/null
+++ b/crypto/secp256r1/verifier.go
@@ -0,0 +1,39 @@
+package secp256r1
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"errors"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/common"
+)
+
+var (
+	secp256k1halfN = new(big.Int).Div(elliptic.P256().Params().N, big.NewInt(2))
+)
+
+// Verifies the given signature (r, s) for the given hash and public key (x, y).
+func Verify(hash []byte, r, s, x, y *big.Int) ([]byte, error) {
+	// Create the public key format
+	publicKey := newPublicKey(x, y)
+	if publicKey == nil {
+		return nil, errors.New("invalid public key coordinates")
+	}
+
+	if checkMalleability(s) {
+		return nil, errors.New("malleability issue")
+	}
+
+	// Verify the signature with the public key and return 1 if it's valid, 0 otherwise
+	if ok := ecdsa.Verify(publicKey, hash, r, s); ok {
+		return common.LeftPadBytes(common.Big1.Bytes(), 32), nil
+	}
+
+	return common.LeftPadBytes(common.Big0.Bytes(), 32), nil
+}
+
+// Check the malleability issue
+func checkMalleability(s *big.Int) bool {
+	return s.Cmp(secp256k1halfN) <= 0
+}