Merge pull request #61 from keep-network/signer

EthereumSigner and local Signer

EthereumSigner provides functions to sign a message and verify a
signature using Ethereum-specific signature format. It also provides
functions for the conversion of a public key to address.

The code has been extracted from `keep-core` with slight modifications
that will allow it to be imported from `keep-core` and `keep-ecdsa`.

The code is being extracted to allow us decouple ethereum-specific
implementation functions we use in generic code of `keep-ecdsa` client,
especially in `node.go`.

Also extracted `localSigning` from `keep-core` as a `local.Signer`.
Having `local` `Signer` implementation in `keep-common` will let us not
duplicate the code between local chain implementations in `keep-core`
and `keep-ecdsa`.

pkg/chain/ethereum/ethutil/signer.go

@@ -0,0 +1,144 @@
+package ethutil
+
+import (
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/crypto"
+)
+
+// SignatureSize is a byte size of a signature calculated by Ethereum with
+// recovery-id, V, included. The signature consists of three values (R,S,V)
+// in the following order:
+// R = [0:31]
+// S = [32:63]
+// V = [64]
+const SignatureSize = 65
+
+// EthereumSigner provides functions to sign a message and verify a signature
+// using the Ethereum-specific signature format. It also provides functions for
+// conversion of a public key to an address.
+type EthereumSigner struct {
+	privateKey *ecdsa.PrivateKey
+}
+
+// NewSigner creates a new EthereumSigner instance for the provided ECDSA
+// private key.
+func NewSigner(privateKey *ecdsa.PrivateKey) *EthereumSigner {
+	return &EthereumSigner{privateKey}
+}
+
+// PublicKey returns byte representation of a public key for the private key
+// signer was created with.
+func (es *EthereumSigner) PublicKey() []byte {
+	publicKey := es.privateKey.PublicKey
+	return elliptic.Marshal(publicKey.Curve, publicKey.X, publicKey.Y)
+}
+
+// Sign signs the provided message using Ethereum-specific format.
+func (es *EthereumSigner) Sign(message []byte) ([]byte, error) {
+	signature, err := crypto.Sign(ethereumPrefixedHash(message), es.privateKey)
+	if err != nil {
+		return nil, err
+	}
+
+	if len(signature) == SignatureSize {
+		// go-ethereum/crypto produces signature with v={0, 1} and we need to add
+		// 27 to v-part (signature[64]) to conform with the on-chain signature
+		// validation code that accepts v={27, 28} as specified in the
+		// Appendix F of the Ethereum Yellow Paper
+		// https://ethereum.github.io/yellowpaper/paper.pdf
+		signature[len(signature)-1] = signature[len(signature)-1] + 27
+	}
+
+	return signature, nil
+}
+
+// Verify verifies the provided message against a signature using the key
+// EthereumSigner was created with. The signature has to be provided in
+// Ethereum-specific format.
+func (es *EthereumSigner) Verify(message []byte, signature []byte) (bool, error) {
+	return verifySignature(message, signature, &es.privateKey.PublicKey)
+}
+
+// VerifyWithPublicKey verifies the provided message against a signature and
+// public key. The signature has to be provided in Ethereum-specific format.
+func (es *EthereumSigner) VerifyWithPublicKey(
+	message []byte,
+	signature []byte,
+	publicKey []byte,
+) (bool, error) {
+	unmarshalledPubKey, err := unmarshalPublicKey(
+		publicKey,
+		es.privateKey.Curve,
+	)
+	if err != nil {
+		return false, fmt.Errorf("failed to unmarshal public key: [%v]", err)
+	}
+
+	return verifySignature(message, signature, unmarshalledPubKey)
+}
+
+func verifySignature(
+	message []byte,
+	signature []byte,
+	publicKey *ecdsa.PublicKey,
+) (bool, error) {
+	// Convert the operator's static key into an uncompressed public key
+	// which should be 65 bytes in length.
+	uncompressedPubKey := crypto.FromECDSAPub(publicKey)
+	// If our signature is in the [R || S || V] format, ensure we strip out
+	// the Ethereum-specific recovery-id, V, if it already hasn't been done.
+	if len(signature) == SignatureSize {
+		signature = signature[:len(signature)-1]
+	}
+
+	// The signature should be now 64 bytes long.
+	if len(signature) != 64 {
+		return false, fmt.Errorf(
+			"signature should have 64 bytes; has: [%d]",
+			len(signature),
+		)
+	}
+
+	return crypto.VerifySignature(
+		uncompressedPubKey,
+		ethereumPrefixedHash(message),
+		signature,
+	), nil
+}
+
+func ethereumPrefixedHash(message []byte) []byte {
+	return crypto.Keccak256(
+		[]byte(fmt.Sprintf("\x19Ethereum Signed Message:\n%v", len(message))),
+		message,
+	)
+}
+
+func unmarshalPublicKey(
+	bytes []byte,
+	curve elliptic.Curve,
+) (*ecdsa.PublicKey, error) {
+	x, y := elliptic.Unmarshal(curve, bytes)
+	if x == nil {
+		return nil, fmt.Errorf(
+			"invalid public key bytes",
+		)
+	}
+	ecdsaPublicKey := &ecdsa.PublicKey{Curve: curve, X: x, Y: y}
+	return (*ecdsa.PublicKey)(ecdsaPublicKey), nil
+}
+
+// PublicKeyToAddress transforms the provided ECDSA public key into Ethereum
+// address represented in bytes.
+func (es *EthereumSigner) PublicKeyToAddress(publicKey ecdsa.PublicKey) []byte {
+	return crypto.PubkeyToAddress(publicKey).Bytes()
+}
+
+// PublicKeyBytesToAddress transforms the provided ECDSA public key in a bytes
+// format into Ethereum address represented in bytes.
+func (es *EthereumSigner) PublicKeyBytesToAddress(publicKey []byte) []byte {
+	// Does the same as crypto.PubkeyToAddress but directly on public key bytes.
+	return crypto.Keccak256(publicKey[1:])[12:]
+}

pkg/chain/ethereum/ethutil/signer_test.go

@@ -0,0 +1,165 @@
+package ethutil
+
+import (
+	"testing"
+
+	"github.com/ethereum/go-ethereum/crypto"
+)
+
+func TestSignAndVerify(t *testing.T) {
+	signer, err := newSigner()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	message := []byte("He that breaks a thing to find out what it is, has " +
+		"left the path of wisdom.")
+
+	signature, err := signer.Sign(message)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var tests = map[string]struct {
+		message                 []byte
+		signature               []byte
+		validSignatureExpected  bool
+		validationErrorExpected bool
+	}{
+		"valid signature for message": {
+			message:                 message,
+			signature:               signature,
+			validSignatureExpected:  true,
+			validationErrorExpected: false,
+		},
+		"invalid signature for message": {
+			message:                 []byte("I am sorry"),
+			signature:               signature,
+			validSignatureExpected:  false,
+			validationErrorExpected: false,
+		},
+		"corrupted signature": {
+			message:                 message,
+			signature:               []byte("I am so sorry"),
+			validSignatureExpected:  false,
+			validationErrorExpected: true,
+		},
+	}
+
+	for testName, test := range tests {
+		t.Run(testName, func(t *testing.T) {
+			ok, err := signer.Verify(test.message, test.signature)
+
+			if !ok && test.validSignatureExpected {
+				t.Errorf("expected valid signature but verification failed")
+			}
+			if ok && !test.validSignatureExpected {
+				t.Errorf("expected invalid signature but verification succeeded")
+			}
+
+			if err == nil && test.validationErrorExpected {
+				t.Errorf("expected signature validation error; none happened")
+			}
+			if err != nil && !test.validationErrorExpected {
+				t.Errorf("unexpected signature validation error [%v]", err)
+			}
+		})
+	}
+}
+
+func TestSignAndVerifyWithProvidedPublicKey(t *testing.T) {
+	message := []byte("I am looking for someone to share in an adventure")
+
+	signer1, err := newSigner()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	signer2, err := newSigner()
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	publicKey := signer1.PublicKey()
+	signature, err := signer1.Sign(message)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	var tests = map[string]struct {
+		message                 []byte
+		signature               []byte
+		publicKey               []byte
+		validSignatureExpected  bool
+		validationErrorExpected bool
+	}{
+		"valid signature for message": {
+			message:                 message,
+			signature:               signature,
+			publicKey:               publicKey,
+			validSignatureExpected:  true,
+			validationErrorExpected: false,
+		},
+		"invalid signature for message": {
+			message:                 []byte("And here..."),
+			signature:               signature,
+			publicKey:               publicKey,
+			validSignatureExpected:  false,
+			validationErrorExpected: false,
+		},
+		"corrupted signature": {
+			message:                 message,
+			signature:               []byte("we..."),
+			publicKey:               publicKey,
+			validSignatureExpected:  false,
+			validationErrorExpected: true,
+		},
+		"invalid remote public key": {
+			message:                 message,
+			signature:               signature,
+			publicKey:               signer2.PublicKey(),
+			validSignatureExpected:  false,
+			validationErrorExpected: false,
+		},
+		"corrupted remote public key": {
+			message:                 message,
+			signature:               signature,
+			publicKey:               []byte("go..."),
+			validSignatureExpected:  false,
+			validationErrorExpected: true,
+		},
+	}
+
+	for testName, test := range tests {
+		t.Run(testName, func(t *testing.T) {
+			ok, err := signer2.VerifyWithPublicKey(
+				test.message,
+				test.signature,
+				test.publicKey,
+			)
+
+			if !ok && test.validSignatureExpected {
+				t.Errorf("expected valid signature but verification failed")
+			}
+			if ok && !test.validSignatureExpected {
+				t.Errorf("expected invalid signature but verification succeeded")
+			}
+
+			if err == nil && test.validationErrorExpected {
+				t.Errorf("expected signature validation error; none happened")
+			}
+			if err != nil && !test.validationErrorExpected {
+				t.Errorf("unexpected signature validation error [%v]", err)
+			}
+		})
+	}
+}
+
+func newSigner() (*EthereumSigner, error) {
+	key, err := crypto.GenerateKey()
+	if err != nil {
+		return nil, err
+	}
+
+	return &EthereumSigner{key}, nil
+}