whisper: remove AESNonce from envelope in v6

The aes nonce is now part of the payload of a symmetric
message. Since there is no futher available indication
whether a message is symmetric or not, functions
isSymmetric and isAsymmetric have been removed and
a symmetric topic match will be attempted if the filter
is symmetric. Accordingly, other checks have been
removed at the top level, because they can no longer
be performed until it is known for a fact that the
message uses symmetric encryption.

whisper/whisperv6/envelope.go

@@ -40,7 +40,6 @@ type Envelope struct {
 	Expiry   uint32
 	TTL      uint32
 	Topic    TopicType
-	AESNonce []byte
 	Data     []byte
 	Nonce    uint64
 
@@ -51,12 +50,12 @@ type Envelope struct {
 
 // size returns the size of envelope as it is sent (i.e. public fields only)
 func (e *Envelope) size() int {
-	return 20 + len(e.Version) + len(e.AESNonce) + len(e.Data)
+	return 20 + len(e.Version) + len(e.Data)
 }
 
 // rlpWithoutNonce returns the RLP encoded envelope contents, except the nonce.
 func (e *Envelope) rlpWithoutNonce() []byte {
-	res, _ := rlp.EncodeToBytes([]interface{}{e.Version, e.Expiry, e.TTL, e.Topic, e.AESNonce, e.Data})
+	res, _ := rlp.EncodeToBytes([]interface{}{e.Version, e.Expiry, e.TTL, e.Topic, e.Data})
 	return res
 }
 
@@ -82,14 +81,6 @@ func NewEnvelope(ttl uint32, topic TopicType, aesNonce []byte, msg *sentMessage)
 	return &env
 }
 
-func (e *Envelope) IsSymmetric() bool {
-	return len(e.AESNonce) > 0
-}
-
-func (e *Envelope) isAsymmetric() bool {
-	return !e.IsSymmetric()
-}
-
 func (e *Envelope) Ver() uint64 {
 	return bytesToUintLittleEndian(e.Version)
 }
@@ -209,7 +200,7 @@ func (e *Envelope) OpenAsymmetric(key *ecdsa.PrivateKey) (*ReceivedMessage, erro
 // OpenSymmetric tries to decrypt an envelope, potentially encrypted with a particular key.
 func (e *Envelope) OpenSymmetric(key []byte) (msg *ReceivedMessage, err error) {
 	msg = &ReceivedMessage{Raw: e.Data}
-	err = msg.decryptSymmetric(key, e.AESNonce)
+	err = msg.decryptSymmetric(key)
 	if err != nil {
 		msg = nil
 	}
@@ -218,12 +209,17 @@ func (e *Envelope) OpenSymmetric(key []byte) (msg *ReceivedMessage, err error) {
 
 // Open tries to decrypt an envelope, and populates the message fields in case of success.
 func (e *Envelope) Open(watcher *Filter) (msg *ReceivedMessage) {
-	if e.isAsymmetric() {
+	// if the filter has some asymmetric key provided, it will
+	// attempt to open it asymmetrically. If this fails, then
+	// attempt to open it symmetrically.
+	if watcher.KeyAsym != nil {
 		msg, _ = e.OpenAsymmetric(watcher.KeyAsym)
 		if msg != nil {
 			msg.Dst = &watcher.KeyAsym.PublicKey
 		}
-	} else if e.IsSymmetric() {
+	}
+
+	if msg == nil {
 		msg, _ = e.OpenSymmetric(watcher.KeySym)
 		if msg != nil {
 			msg.SymKeyHash = crypto.Keccak256Hash(watcher.KeySym)

whisper/whisperv6/filter.go

@@ -175,6 +175,9 @@ func (f *Filter) Retrieve() (all []*ReceivedMessage) {
 	return all
 }
 
+// MatchMessage checks if the filter matches an already decrypted
+// message (i.e. a Message that has already been handled by
+// MatchEnvelope when checked by a previous filter)
 func (f *Filter) MatchMessage(msg *ReceivedMessage) bool {
 	if f.PoW > 0 && msg.PoW < f.PoW {
 		return false
@@ -188,17 +191,15 @@ func (f *Filter) MatchMessage(msg *ReceivedMessage) bool {
 	return false
 }
 
+// MatchEvelope checks if it's worth decrypting the message. If
+// it returns `true`, client code is expected to attempt decrypting
+// the message and subsequently call MatchMessage.
 func (f *Filter) MatchEnvelope(envelope *Envelope) bool {
 	if f.PoW > 0 && envelope.pow < f.PoW {
 		return false
 	}
 
-	if f.expectsAsymmetricEncryption() && envelope.isAsymmetric() {
 	return f.MatchTopic(envelope.Topic)
-	} else if f.expectsSymmetricEncryption() && envelope.IsSymmetric() {
-		return f.MatchTopic(envelope.Topic)
-	}
-	return false
 }
 
 func (f *Filter) MatchTopic(topic TopicType) bool {

whisper/whisperv6/filter_test.go

@@ -312,12 +312,6 @@ func TestMatchEnvelope(t *testing.T) {
 		t.Fatalf("failed MatchEnvelope() symmetric with seed %d.", seed)
 	}
 
-	// asymmetric + matching topic: mismatch
-	match = fasym.MatchEnvelope(env)
-	if match {
-		t.Fatalf("failed MatchEnvelope() asymmetric with seed %d.", seed)
-	}
-
 	// symmetric + matching topic + insufficient PoW: mismatch
 	fsym.PoW = env.PoW() + 1.0
 	match = fsym.MatchEnvelope(env)

whisper/whisperv6/message.go

@@ -61,6 +61,7 @@ type ReceivedMessage struct {
 	Payload   []byte
 	Padding   []byte
 	Signature []byte
+	Salt      []byte
 
 	PoW   float64          // Proof of work as described in the Whisper spec
 	Sent  uint32           // Time when the message was posted into the network
@@ -196,31 +197,31 @@ func (msg *sentMessage) encryptAsymmetric(key *ecdsa.PublicKey) error {
 
 // encryptSymmetric encrypts a message with a topic key, using AES-GCM-256.
 // nonce size should be 12 bytes (see cipher.gcmStandardNonceSize).
-func (msg *sentMessage) encryptSymmetric(key []byte) (nonce []byte, err error) {
+func (msg *sentMessage) encryptSymmetric(key []byte) (err error) {
 	if !validateSymmetricKey(key) {
-		return nil, errors.New("invalid key provided for symmetric encryption")
+		return errors.New("invalid key provided for symmetric encryption")
 	}
 
 	block, err := aes.NewCipher(key)
 	if err != nil {
-		return nil, err
+		return err
 	}
 	aesgcm, err := cipher.NewGCM(block)
 	if err != nil {
-		return nil, err
+		return err
 	}
 
 	// never use more than 2^32 random nonces with a given key
-	nonce = make([]byte, aesgcm.NonceSize())
+	salt := make([]byte, aesgcm.NonceSize())
-	_, err = crand.Read(nonce)
+	_, err = crand.Read(salt)
 	if err != nil {
-		return nil, err
+		return err
-	} else if !validateSymmetricKey(nonce) {
+	} else if !validateSymmetricKey(salt) {
-		return nil, errors.New("crypto/rand failed to generate nonce")
+		return errors.New("crypto/rand failed to generate salt")
 	}
 
-	msg.Raw = aesgcm.Seal(nil, nonce, msg.Raw, nil)
+	msg.Raw = append(aesgcm.Seal(nil, salt, msg.Raw, nil), salt...)
-	return nonce, nil
+	return nil
 }
 
 // Wrap bundles the message into an Envelope to transmit over the network.
@@ -233,11 +234,10 @@ func (msg *sentMessage) Wrap(options *MessageParams) (envelope *Envelope, err er
 			return nil, err
 		}
 	}
-	var nonce []byte
 	if options.Dst != nil {
 		err = msg.encryptAsymmetric(options.Dst)
 	} else if options.KeySym != nil {
-		nonce, err = msg.encryptSymmetric(options.KeySym)
+		err = msg.encryptSymmetric(options.KeySym)
 	} else {
 		err = errors.New("unable to encrypt the message: neither symmetric nor assymmetric key provided")
 	}
@@ -245,7 +245,7 @@ func (msg *sentMessage) Wrap(options *MessageParams) (envelope *Envelope, err er
 		return nil, err
 	}
 
-	envelope = NewEnvelope(options.TTL, options.Topic, nonce, msg)
+	envelope = NewEnvelope(options.TTL, options.Topic, msg)
 	if err = envelope.Seal(options); err != nil {
 		return nil, err
 	}
@@ -254,7 +254,14 @@ func (msg *sentMessage) Wrap(options *MessageParams) (envelope *Envelope, err er
 
 // decryptSymmetric decrypts a message with a topic key, using AES-GCM-256.
 // nonce size should be 12 bytes (see cipher.gcmStandardNonceSize).
-func (msg *ReceivedMessage) decryptSymmetric(key []byte, nonce []byte) error {
+func (msg *ReceivedMessage) decryptSymmetric(key []byte) error {
+	// In v6, symmetric messages are expected to contain the 12-byte
+	// "salt" at the end of the payload.
+	if len(msg.Raw) < AESNonceLength {
+		return errors.New("missing salt or invalid payload in symmetric message")
+	}
+	salt := msg.Raw[len(msg.Raw)-AESNonceLength:]
+
 	block, err := aes.NewCipher(key)
 	if err != nil {
 		return err
@@ -263,15 +270,16 @@ func (msg *ReceivedMessage) decryptSymmetric(key []byte, nonce []byte) error {
 	if err != nil {
 		return err
 	}
-	if len(nonce) != aesgcm.NonceSize() {
+	if len(salt) != aesgcm.NonceSize() {
-		log.Error("decrypting the message", "AES nonce size", len(nonce))
+		log.Error("decrypting the message", "AES salt size", len(salt))
-		return errors.New("wrong AES nonce size")
+		return errors.New("wrong AES salt size")
 	}
-	decrypted, err := aesgcm.Open(nil, nonce, msg.Raw, nil)
+	decrypted, err := aesgcm.Open(nil, salt, msg.Raw[:len(msg.Raw)-AESNonceLength], nil)
 	if err != nil {
 		return err
 	}
 	msg.Raw = decrypted
+	msg.Salt = salt
 	return nil
 }
 

whisper/whisperv6/message_test.go

@@ -174,10 +174,8 @@ func TestMessageSeal(t *testing.T) {
 		t.Fatalf("failed to create new message with seed %d: %s.", seed, err)
 	}
 	params.TTL = 1
-	aesnonce := make([]byte, 12)
-	mrand.Read(aesnonce)
 
-	env := NewEnvelope(params.TTL, params.Topic, aesnonce, msg)
+	env := NewEnvelope(params.TTL, params.Topic, msg)
 	if err != nil {
 		t.Fatalf("failed Wrap with seed %d: %s.", seed, err)
 	}

whisper/whisperv6/whisper.go

@@ -591,13 +591,6 @@ func (wh *Whisper) add(envelope *Envelope) (bool, error) {
 		return false, fmt.Errorf("oversized version [%x]", envelope.Hash())
 	}
 
-	aesNonceSize := len(envelope.AESNonce)
-	if aesNonceSize != 0 && aesNonceSize != AESNonceLength {
-		// the standard AES GCM nonce size is 12 bytes,
-		// but constant gcmStandardNonceSize cannot be accessed (not exported)
-		return false, fmt.Errorf("wrong size of AESNonce: %d bytes [env: %x]", aesNonceSize, envelope.Hash())
-	}
-
 	if envelope.PoW() < wh.MinPow() {
 		log.Debug("envelope with low PoW dropped", "PoW", envelope.PoW(), "hash", envelope.Hash().Hex())
 		return false, nil // drop envelope without error