sphinx: rename obfuscation.go to onion_error.go

crypto.go

@@ -147,3 +147,17 @@ func generateSharedSecret(pub *btcec.PublicKey, priv *btcec.PrivateKey) Hash256
 
 	return sha256.Sum256(s.SerializeCompressed())
 }
+
+// onionEncrypt obfuscates the data with compliance with BOLT#4. As we use a
+// stream cipher, calling onionEncrypt on an already encrypted piece of data
+// will decrypt it.
+func onionEncrypt(sharedSecret *Hash256, data []byte) []byte {
+
+	p := make([]byte, len(data))
+
+	ammagKey := generateKey("ammag", sharedSecret)
+	streamBytes := generateCipherStream(ammagKey, uint(len(data)))
+	xor(p, data, streamBytes)
+
+	return p
+}

obfuscation.go → onion_error.go

@@ -5,25 +5,12 @@ import (
 	"crypto/hmac"
 	"crypto/sha256"
 	"errors"
+	"fmt"
 	"io"
 
 	"github.com/btcsuite/btcd/btcec"
 )
 
-// onionEncrypt obfuscates the data with compliance with BOLT#4. As we use a
-// stream cipher, calling onionEncrypt on an already encrypted piece of data
-// will decrypt it.
-func onionEncrypt(sharedSecret *Hash256, data []byte) []byte {
-
-	p := make([]byte, len(data))
-
-	ammagKey := generateKey("ammag", sharedSecret)
-	streamBytes := generateCipherStream(ammagKey, uint(len(data)))
-	xor(p, data, streamBytes)
-
-	return p
-}
-
 // OnionErrorEncrypter is a struct that's used to implement onion error
 // encryption as defined within BOLT0004.
 type OnionErrorEncrypter struct {
@@ -166,11 +153,22 @@ func NewOnionErrorDecrypter(circuit *Circuit) *OnionErrorDecrypter {
 	}
 }
 
+// onionErrorLength is the expected length of the onion error message.
+// Including padding, all messages on the wire should be 256 bytes. We then add
+// the size of the sha256 HMAC as well.
+const onionErrorLength = 2 + 2 + 256 + sha256.Size
+
 // DecryptError attempts to decrypt the passed encrypted error response. The
 // onion failure is encrypted in backward manner, starting from the node where
 // error have occurred. As a result, in order to decrypt the error we need get
 // all shared secret and apply decryption in the reverse order.
 func (o *OnionErrorDecrypter) DecryptError(encryptedData []byte) (*btcec.PublicKey, []byte, error) {
+	// Ensure the error message length is as expected.
+	if len(encryptedData) != onionErrorLength {
+		return nil, nil, fmt.Errorf("invalid error length: "+
+			"expected %v got %v", onionErrorLength,
+			len(encryptedData))
+	}
 
 	sharedSecrets := generateSharedSecrets(
 		o.circuit.PaymentPath,

obfuscation_test.go → onion_error_test.go

@@ -2,6 +2,7 @@ package sphinx
 
 import (
 	"bytes"
+	"crypto/sha256"
 	"encoding/hex"
 	"reflect"
 	"testing"
@@ -28,7 +29,7 @@ func TestOnionFailure(t *testing.T) {
 	// able to receive the error not only from last hop.
 	errorPath := paymentPath[:len(paymentPath)-1]
 
-	failureData := []byte("some kek-error data")
+	failureData := bytes.Repeat([]byte{'A'}, onionErrorLength-sha256.Size)
 	sharedSecrets := generateSharedSecrets(paymentPath, sessionKey)
 
 	// Emulate creation of the obfuscator on node where error have occurred.