crypto: replace ToECDSAPub with error-checking func UnmarshalPubkey (#16932)

ToECDSAPub was unsafe because it returned a non-nil key with nil X, Y in
case of invalid input. This change replaces ToECDSAPub with
UnmarshalPubkey across the codebase.

2 files changed, 38 insertions, 6 deletions

diff --git a/crypto/crypto.go b/crypto/crypto.go
index 76d1ffaf6..619440e81 100644
--- a/crypto/crypto.go
+++ b/crypto/crypto.go
@@ -39,6 +39,8 @@ var (
 	secp256k1halfN = new(big.Int).Div(secp256k1N, big.NewInt(2))
 )
 
+var errInvalidPubkey = errors.New("invalid secp256k1 public key")
+
 // Keccak256 calculates and returns the Keccak256 hash of the input data.
 func Keccak256(data ...[]byte) []byte {
 	d := sha3.NewKeccak256()
@@ -122,12 +124,13 @@ func FromECDSA(priv *ecdsa.PrivateKey) []byte {
 	return math.PaddedBigBytes(priv.D, priv.Params().BitSize/8)
 }
 
-func ToECDSAPub(pub []byte) *ecdsa.PublicKey {
-	if len(pub) == 0 {
-		return nil
-	}
+// UnmarshalPubkey converts bytes to a secp256k1 public key.
+func UnmarshalPubkey(pub []byte) (*ecdsa.PublicKey, error) {
 	x, y := elliptic.Unmarshal(S256(), pub)
-	return &ecdsa.PublicKey{Curve: S256(), X: x, Y: y}
+	if x == nil {
+		return nil, errInvalidPubkey
+	}
+	return &ecdsa.PublicKey{Curve: S256(), X: x, Y: y}, nil
 }
 
 func FromECDSAPub(pub *ecdsa.PublicKey) []byte {
diff --git a/crypto/crypto_test.go b/crypto/crypto_test.go
index 804de3fe2..177c19c0c 100644
--- a/crypto/crypto_test.go
+++ b/crypto/crypto_test.go
@@ -23,9 +23,11 @@ import (
 	"io/ioutil"
 	"math/big"
 	"os"
+	"reflect"
 	"testing"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/common/hexutil"
 )
 
 var testAddrHex = "970e8128ab834e8eac17ab8e3812f010678cf791"
@@ -56,6 +58,33 @@ func BenchmarkSha3(b *testing.B) {
 	}
 }
 
+func TestUnmarshalPubkey(t *testing.T) {
+	key, err := UnmarshalPubkey(nil)
+	if err != errInvalidPubkey || key != nil {
+		t.Fatalf("expected error, got %v, %v", err, key)
+	}
+	key, err = UnmarshalPubkey([]byte{1, 2, 3})
+	if err != errInvalidPubkey || key != nil {
+		t.Fatalf("expected error, got %v, %v", err, key)
+	}
+
+	var (
+		enc, _ = hex.DecodeString("04760c4460e5336ac9bbd87952a3c7ec4363fc0a97bd31c86430806e287b437fd1b01abc6e1db640cf3106b520344af1d58b00b57823db3e1407cbc433e1b6d04d")
+		dec    = &ecdsa.PublicKey{
+			Curve: S256(),
+			X:     hexutil.MustDecodeBig("0x760c4460e5336ac9bbd87952a3c7ec4363fc0a97bd31c86430806e287b437fd1"),
+			Y:     hexutil.MustDecodeBig("0xb01abc6e1db640cf3106b520344af1d58b00b57823db3e1407cbc433e1b6d04d"),
+		}
+	)
+	key, err = UnmarshalPubkey(enc)
+	if err != nil {
+		t.Fatalf("expected no error, got %v", err)
+	}
+	if !reflect.DeepEqual(key, dec) {
+		t.Fatal("wrong result")
+	}
+}
+
 func TestSign(t *testing.T) {
 	key, _ := HexToECDSA(testPrivHex)
 	addr := common.HexToAddress(testAddrHex)
@@ -69,7 +98,7 @@ func TestSign(t *testing.T) {
 	if err != nil {
 		t.Errorf("ECRecover error: %s", err)
 	}
-	pubKey := ToECDSAPub(recoveredPub)
+	pubKey, _ := UnmarshalPubkey(recoveredPub)
 	recoveredAddr := PubkeyToAddress(*pubKey)
 	if addr != recoveredAddr {
 		t.Errorf("Address mismatch: want: %x have: %x", addr, recoveredAddr)