crypto, crypto/ecies, crypto/secp256k1: libsecp256k1 scalar mult

thanks to Felix Lange (fjl) for help with design & impl

4 files changed, 123 insertions, 20 deletions

diff --git a/crypto/ecies/asn1.go b/crypto/ecies/asn1.go
index 6eaf3d2ca..40dabd329 100644
--- a/crypto/ecies/asn1.go
+++ b/crypto/ecies/asn1.go
@@ -41,6 +41,8 @@ import (
 	"fmt"
 	"hash"
 	"math/big"
+
+	"github.com/ethereum/go-ethereum/crypto/secp256k1"
 )
 
 var (
@@ -81,6 +83,7 @@ func doScheme(base, v []int) asn1.ObjectIdentifier {
 type secgNamedCurve asn1.ObjectIdentifier
 
 var (
+	secgNamedCurveS256 = secgNamedCurve{1, 3, 132, 0, 10}
 	secgNamedCurveP256 = secgNamedCurve{1, 2, 840, 10045, 3, 1, 7}
 	secgNamedCurveP384 = secgNamedCurve{1, 3, 132, 0, 34}
 	secgNamedCurveP521 = secgNamedCurve{1, 3, 132, 0, 35}
@@ -116,6 +119,8 @@ func (curve secgNamedCurve) Equal(curve2 secgNamedCurve) bool {
 
 func namedCurveFromOID(curve secgNamedCurve) elliptic.Curve {
 	switch {
+	case curve.Equal(secgNamedCurveS256):
+		return secp256k1.S256()
 	case curve.Equal(secgNamedCurveP256):
 		return elliptic.P256()
 	case curve.Equal(secgNamedCurveP384):
@@ -134,6 +139,8 @@ func oidFromNamedCurve(curve elliptic.Curve) (secgNamedCurve, bool) {
 		return secgNamedCurveP384, true
 	case elliptic.P521():
 		return secgNamedCurveP521, true
+	case secp256k1.S256():
+		return secgNamedCurveS256, true
 	}
 
 	return nil, false
diff --git a/crypto/ecies/ecies.go b/crypto/ecies/ecies.go
index a3b520dd5..65dc5b38b 100644
--- a/crypto/ecies/ecies.go
+++ b/crypto/ecies/ecies.go
@@ -125,6 +125,7 @@ func (prv *PrivateKey) GenerateShared(pub *PublicKey, skLen, macLen int) (sk []b
 	if skLen+macLen > MaxSharedKeyLength(pub) {
 		return nil, ErrSharedKeyTooBig
 	}
+
 	x, _ := pub.Curve.ScalarMult(pub.X, pub.Y, prv.D.Bytes())
 	if x == nil {
 		return nil, ErrSharedKeyIsPointAtInfinity
diff --git a/crypto/ecies/ecies_test.go b/crypto/ecies/ecies_test.go
index 1c391f938..6a0ea3f02 100644
--- a/crypto/ecies/ecies_test.go
+++ b/crypto/ecies/ecies_test.go
@@ -31,13 +31,18 @@ package ecies
 
 import (
 	"bytes"
+	"crypto/ecdsa"
 	"crypto/elliptic"
 	"crypto/rand"
 	"crypto/sha256"
+	"encoding/hex"
 	"flag"
 	"fmt"
 	"io/ioutil"
+	"math/big"
 	"testing"
+
+	"github.com/ethereum/go-ethereum/crypto/secp256k1"
 )
 
 var dumpEnc bool
@@ -65,7 +70,6 @@ func TestKDF(t *testing.T) {
 	}
 }
 
-var skLen int
 var ErrBadSharedKeys = fmt.Errorf("ecies: shared keys don't match")
 
 // cmpParams compares a set of ECIES parameters. We assume, as per the
@@ -117,7 +121,7 @@ func TestSharedKey(t *testing.T) {
 		fmt.Println(err.Error())
 		t.FailNow()
 	}
-	skLen = MaxSharedKeyLength(&prv1.PublicKey) / 2
+	skLen := MaxSharedKeyLength(&prv1.PublicKey) / 2
 
 	prv2, err := GenerateKey(rand.Reader, DefaultCurve, nil)
 	if err != nil {
@@ -143,6 +147,44 @@ func TestSharedKey(t *testing.T) {
 	}
 }
 
+func TestSharedKeyPadding(t *testing.T) {
+	// sanity checks
+	prv0 := hexKey("1adf5c18167d96a1f9a0b1ef63be8aa27eaf6032c233b2b38f7850cf5b859fd9")
+	prv1 := hexKey("97a076fc7fcd9208240668e31c9abee952cbb6e375d1b8febc7499d6e16f1a")
+	x0, _ := new(big.Int).SetString("1a8ed022ff7aec59dc1b440446bdda5ff6bcb3509a8b109077282b361efffbd8", 16)
+	x1, _ := new(big.Int).SetString("6ab3ac374251f638d0abb3ef596d1dc67955b507c104e5f2009724812dc027b8", 16)
+	y0, _ := new(big.Int).SetString("e040bd480b1deccc3bc40bd5b1fdcb7bfd352500b477cb9471366dbd4493f923", 16)
+	y1, _ := new(big.Int).SetString("8ad915f2b503a8be6facab6588731fefeb584fd2dfa9a77a5e0bba1ec439e4fa", 16)
+
+	if prv0.PublicKey.X.Cmp(x0) != 0 {
+		t.Errorf("mismatched prv0.X:\nhave: %x\nwant: %x\n", prv0.PublicKey.X.Bytes(), x0.Bytes())
+	}
+	if prv0.PublicKey.Y.Cmp(y0) != 0 {
+		t.Errorf("mismatched prv0.Y:\nhave: %x\nwant: %x\n", prv0.PublicKey.Y.Bytes(), y0.Bytes())
+	}
+	if prv1.PublicKey.X.Cmp(x1) != 0 {
+		t.Errorf("mismatched prv1.X:\nhave: %x\nwant: %x\n", prv1.PublicKey.X.Bytes(), x1.Bytes())
+	}
+	if prv1.PublicKey.Y.Cmp(y1) != 0 {
+		t.Errorf("mismatched prv1.Y:\nhave: %x\nwant: %x\n", prv1.PublicKey.Y.Bytes(), y1.Bytes())
+	}
+
+	// test shared secret generation
+	sk1, err := prv0.GenerateShared(&prv1.PublicKey, 16, 16)
+	if err != nil {
+		fmt.Println(err.Error())
+	}
+
+	sk2, err := prv1.GenerateShared(&prv0.PublicKey, 16, 16)
+	if err != nil {
+		t.Fatal(err.Error())
+	}
+
+	if !bytes.Equal(sk1, sk2) {
+		t.Fatal(ErrBadSharedKeys.Error())
+	}
+}
+
 // Verify that the key generation code fails when too much key data is
 // requested.
 func TestTooBigSharedKey(t *testing.T) {
@@ -158,13 +200,13 @@ func TestTooBigSharedKey(t *testing.T) {
 		t.FailNow()
 	}
 
-	_, err = prv1.GenerateShared(&prv2.PublicKey, skLen*2, skLen*2)
+	_, err = prv1.GenerateShared(&prv2.PublicKey, 32, 32)
 	if err != ErrSharedKeyTooBig {
 		fmt.Println("ecdh: shared key should be too large for curve")
 		t.FailNow()
 	}
 
-	_, err = prv2.GenerateShared(&prv1.PublicKey, skLen*2, skLen*2)
+	_, err = prv2.GenerateShared(&prv1.PublicKey, 32, 32)
 	if err != ErrSharedKeyTooBig {
 		fmt.Println("ecdh: shared key should be too large for curve")
 		t.FailNow()
@@ -176,25 +218,21 @@ func TestTooBigSharedKey(t *testing.T) {
 func TestMarshalPublic(t *testing.T) {
 	prv, err := GenerateKey(rand.Reader, DefaultCurve, nil)
 	if err != nil {
-		fmt.Println(err.Error())
-		t.FailNow()
+		t.Fatalf("GenerateKey error: %s", err)
 	}
 
 	out, err := MarshalPublic(&prv.PublicKey)
 	if err != nil {
-		fmt.Println(err.Error())
-		t.FailNow()
+		t.Fatalf("MarshalPublic error: %s", err)
 	}
 
 	pub, err := UnmarshalPublic(out)
 	if err != nil {
-		fmt.Println(err.Error())
-		t.FailNow()
+		t.Fatalf("UnmarshalPublic error: %s", err)
 	}
 
 	if !cmpPublic(prv.PublicKey, *pub) {
-		fmt.Println("ecies: failed to unmarshal public key")
-		t.FailNow()
+		t.Fatal("ecies: failed to unmarshal public key")
 	}
 }
 
@@ -304,9 +342,26 @@ func BenchmarkGenSharedKeyP256(b *testing.B) {
 		fmt.Println(err.Error())
 		b.FailNow()
 	}
+	b.ResetTimer()
+	for i := 0; i < b.N; i++ {
+		_, err := prv.GenerateShared(&prv.PublicKey, 16, 16)
+		if err != nil {
+			fmt.Println(err.Error())
+			b.FailNow()
+		}
+	}
+}
 
+// Benchmark the generation of S256 shared keys.
+func BenchmarkGenSharedKeyS256(b *testing.B) {
+	prv, err := GenerateKey(rand.Reader, secp256k1.S256(), nil)
+	if err != nil {
+		fmt.Println(err.Error())
+		b.FailNow()
+	}
+	b.ResetTimer()
 	for i := 0; i < b.N; i++ {
-		_, err := prv.GenerateShared(&prv.PublicKey, skLen, skLen)
+		_, err := prv.GenerateShared(&prv.PublicKey, 16, 16)
 		if err != nil {
 			fmt.Println(err.Error())
 			b.FailNow()
@@ -511,3 +566,43 @@ func TestBasicKeyValidation(t *testing.T) {
 		}
 	}
 }
+
+// Verify GenerateShared against static values - useful when
+// debugging changes in underlying libs
+func TestSharedKeyStatic(t *testing.T) {
+	prv1 := hexKey("7ebbc6a8358bc76dd73ebc557056702c8cfc34e5cfcd90eb83af0347575fd2ad")
+	prv2 := hexKey("6a3d6396903245bba5837752b9e0348874e72db0c4e11e9c485a81b4ea4353b9")
+
+	skLen := MaxSharedKeyLength(&prv1.PublicKey) / 2
+
+	sk1, err := prv1.GenerateShared(&prv2.PublicKey, skLen, skLen)
+	if err != nil {
+		fmt.Println(err.Error())
+		t.FailNow()
+	}
+
+	sk2, err := prv2.GenerateShared(&prv1.PublicKey, skLen, skLen)
+	if err != nil {
+		fmt.Println(err.Error())
+		t.FailNow()
+	}
+
+	if !bytes.Equal(sk1, sk2) {
+		fmt.Println(ErrBadSharedKeys.Error())
+		t.FailNow()
+	}
+
+	sk, _ := hex.DecodeString("167ccc13ac5e8a26b131c3446030c60fbfac6aa8e31149d0869f93626a4cdf62")
+	if !bytes.Equal(sk1, sk) {
+		t.Fatalf("shared secret mismatch: want: %x have: %x", sk, sk1)
+	}
+}
+
+// TODO: remove after refactoring packages crypto and crypto/ecies
+func hexKey(prv string) *PrivateKey {
+	priv := new(ecdsa.PrivateKey)
+	priv.PublicKey.Curve = secp256k1.S256()
+	priv.D, _ = new(big.Int).SetString(prv, 16)
+	priv.PublicKey.X, priv.PublicKey.Y = secp256k1.S256().ScalarBaseMult(priv.D.Bytes())
+	return ImportECDSA(priv)
+}
diff --git a/crypto/ecies/params.go b/crypto/ecies/params.go
index 97ddb0973..511c53ebc 100644
--- a/crypto/ecies/params.go
+++ b/crypto/ecies/params.go
@@ -41,13 +41,12 @@ import (
 	"crypto/sha512"
 	"fmt"
 	"hash"
-)
 
-// The default curve for this package is the NIST P256 curve, which
-// provides security equivalent to AES-128.
-var DefaultCurve = elliptic.P256()
+	"github.com/ethereum/go-ethereum/crypto/secp256k1"
+)
 
 var (
+	DefaultCurve                  = secp256k1.S256()
 	ErrUnsupportedECDHAlgorithm   = fmt.Errorf("ecies: unsupported ECDH algorithm")
 	ErrUnsupportedECIESParameters = fmt.Errorf("ecies: unsupported ECIES parameters")
 )
@@ -101,9 +100,10 @@ var (
 )
 
 var paramsFromCurve = map[elliptic.Curve]*ECIESParams{
-	elliptic.P256(): ECIES_AES128_SHA256,
-	elliptic.P384(): ECIES_AES256_SHA384,
-	elliptic.P521(): ECIES_AES256_SHA512,
+	secp256k1.S256(): ECIES_AES128_SHA256,
+	elliptic.P256():  ECIES_AES128_SHA256,
+	elliptic.P384():  ECIES_AES256_SHA384,
+	elliptic.P521():  ECIES_AES256_SHA512,
 }
 
 func AddParamsForCurve(curve elliptic.Curve, params *ECIESParams) {