From 98db48ef81b43ff9309546a83f0cd5e0125374b4 Mon Sep 17 00:00:00 2001
From: Richard Ramos <info@richardramos.me>
Date: Thu, 2 Dec 2021 03:24:12 -0400
Subject: [PATCH] generate ecdsa public key from an input public key (#219)

---
 crypto/ecdsa.go      |  5 +++++
 crypto/ecdsa_test.go | 46 ++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 51 insertions(+)

diff --git a/crypto/ecdsa.go b/crypto/ecdsa.go
index 9f8c67e..ea800ce 100644
--- a/crypto/ecdsa.go
+++ b/crypto/ecdsa.go
@@ -67,6 +67,11 @@ func ECDSAKeyPairFromKey(priv *ecdsa.PrivateKey) (PrivKey, PubKey, error) {
 	return &ECDSAPrivateKey{priv}, &ECDSAPublicKey{&priv.PublicKey}, nil
 }
 
+// ECDSAPublicKeyFromPubKey generates a new ecdsa public key from an input public key
+func ECDSAPublicKeyFromPubKey(pub ecdsa.PublicKey) (PubKey, error) {
+	return &ECDSAPublicKey{pub: &pub}, nil
+}
+
 // MarshalECDSAPrivateKey returns x509 bytes from a private key
 func MarshalECDSAPrivateKey(ePriv ECDSAPrivateKey) ([]byte, error) {
 	return x509.MarshalECPrivateKey(ePriv.priv)
diff --git a/crypto/ecdsa_test.go b/crypto/ecdsa_test.go
index eb4d181..cc75d57 100644
--- a/crypto/ecdsa_test.go
+++ b/crypto/ecdsa_test.go
@@ -1,6 +1,7 @@
 package crypto
 
 import (
+	"crypto/ecdsa"
 	"crypto/rand"
 	"testing"
 )
@@ -94,3 +95,48 @@ func TestECDSAMarshalLoop(t *testing.T) {
 	}
 
 }
+
+func TestECDSAPublicKeyFromPubKey(t *testing.T) {
+	ecdsaPrivK, err := ecdsa.GenerateKey(ECDSACurve, rand.Reader)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	privK, _, err := ECDSAKeyPairFromKey(ecdsaPrivK)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	data := []byte("Hello world!")
+	signature, err := privK.Sign(data)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	pubKey, err := ECDSAPublicKeyFromPubKey(ecdsaPrivK.PublicKey)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	ok, err := pubKey.Verify(data, signature)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !ok {
+		t.Fatal("signature didn't match")
+	}
+
+	pubB, err := MarshalPublicKey(pubKey)
+	if err != nil {
+		t.Fatal(err)
+	}
+	pubNew, err := UnmarshalPublicKey(pubB)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !pubKey.Equals(pubNew) || !pubNew.Equals(pubKey) {
+		t.Fatal("keys are not equal")
+	}
+}