les: optional signed announce messages

les/handler.go

@@ -365,11 +365,23 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 	// Block header query, collect the requested headers and reply
 	case AnnounceMsg:
 		p.Log().Trace("Received announce message")
+		if p.requestAnnounceType == announceTypeNone {
+			return errResp(ErrUnexpectedResponse, "")
+		}
 
 		var req announceData
 		if err := msg.Decode(&req); err != nil {
 			return errResp(ErrDecode, "%v: %v", msg, err)
 		}
+
+		if p.requestAnnounceType == announceTypeSigned {
+			if err := req.checkSignature(p.pubKey); err != nil {
+				p.Log().Trace("Invalid announcement signature", "err", err)
+				return err
+			}
+			p.Log().Trace("Valid announcement signature")
+		}
+
 		p.Log().Trace("Announce message content", "number", req.Number, "hash", req.Hash, "td", req.Td, "reorg", req.ReorgDepth)
 		if pm.fetcher != nil {
 			pm.fetcher.announce(p, &req)

les/peer.go

@@ -18,6 +18,7 @@
 package les
 
 import (
+	"crypto/ecdsa"
 	"encoding/binary"
 	"errors"
 	"fmt"
@@ -42,14 +43,23 @@ var (
 
 const maxResponseErrors = 50 // number of invalid responses tolerated (makes the protocol less brittle but still avoids spam)
 
+const (
+	announceTypeNone = iota
+	announceTypeSimple
+	announceTypeSigned
+)
+
 type peer struct {
 	*p2p.Peer
+	pubKey *ecdsa.PublicKey
 
 	rw p2p.MsgReadWriter
 
 	version int    // Protocol version negotiated
 	network uint64 // Network ID being on
 
+	announceType, requestAnnounceType uint64
+
 	id string
 
 	headInfo *announceData
@@ -70,9 +80,11 @@ type peer struct {
 
 func newPeer(version int, network uint64, p *p2p.Peer, rw p2p.MsgReadWriter) *peer {
 	id := p.ID()
+	pubKey, _ := id.Pubkey()
 
 	return &peer{
 		Peer:        p,
+		pubKey:      pubKey,
 		rw:          rw,
 		version:     version,
 		network:     network,
@@ -325,7 +337,7 @@ func (l keyValueList) decode() keyValueMap {
 func (m keyValueMap) get(key string, val interface{}) error {
 	enc, ok := m[key]
 	if !ok {
-		return errResp(ErrHandshakeMissingKey, "%s", key)
+		return errResp(ErrMissingKey, "%s", key)
 	}
 	if val == nil {
 		return nil
@@ -384,6 +396,9 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 		list := server.fcCostStats.getCurrentList()
 		send = send.add("flowControl/MRC", list)
 		p.fcCosts = list.decode()
+	} else {
+		p.requestAnnounceType = announceTypeSimple // set to default until "very light" client mode is implemented
+		send = send.add("announceType", p.requestAnnounceType)
 	}
 	recvList, err := p.sendReceiveHandshake(send)
 	if err != nil {
@@ -428,6 +443,9 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 		/*if recv.get("serveStateSince", nil) == nil {
 			return errResp(ErrUselessPeer, "wanted client, got server")
 		}*/
+		if recv.get("announceType", &p.announceType) != nil {
+			p.announceType = announceTypeSimple
+		}
 		p.fcClient = flowcontrol.NewClientNode(server.fcManager, server.defParams)
 	} else {
 		if recv.get("serveChainSince", nil) != nil {

les/protocol.go

@@ -18,11 +18,17 @@
 package les
 
 import (
+	"bytes"
+	"crypto/ecdsa"
+	"crypto/elliptic"
+	"errors"
 	"fmt"
 	"io"
 	"math/big"
 
 	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/crypto/secp256k1"
 	"github.com/ethereum/go-ethereum/rlp"
 )
 
@@ -88,7 +94,7 @@ const (
 	ErrUnexpectedResponse
 	ErrInvalidResponse
 	ErrTooManyTimeouts
-	ErrHandshakeMissingKey
+	ErrMissingKey
 )
 
 func (e errCode) String() string {
@@ -110,7 +116,13 @@ var errorToString = map[int]string{
 	ErrUnexpectedResponse:      "Unexpected response",
 	ErrInvalidResponse:         "Invalid response",
 	ErrTooManyTimeouts:         "Too many request timeouts",
-	ErrHandshakeMissingKey:     "Key missing from handshake message",
+	ErrMissingKey:              "Key missing from list",
+}
+
+type announceBlock struct {
+	Hash   common.Hash // Hash of one particular block being announced
+	Number uint64      // Number of one particular block being announced
+	Td     *big.Int    // Total difficulty of one particular block being announced
 }
 
 // announceData is the network packet for the block announcements.
@@ -122,6 +134,32 @@ type announceData struct {
 	Update     keyValueList
 }
 
+// sign adds a signature to the block announcement by the given privKey
+func (a *announceData) sign(privKey *ecdsa.PrivateKey) {
+	rlp, _ := rlp.EncodeToBytes(announceBlock{a.Hash, a.Number, a.Td})
+	sig, _ := crypto.Sign(crypto.Keccak256(rlp), privKey)
+	a.Update = a.Update.add("sign", sig)
+}
+
+// checkSignature verifies if the block announcement has a valid signature by the given pubKey
+func (a *announceData) checkSignature(pubKey *ecdsa.PublicKey) error {
+	var sig []byte
+	if err := a.Update.decode().get("sign", &sig); err != nil {
+		return err
+	}
+	rlp, _ := rlp.EncodeToBytes(announceBlock{a.Hash, a.Number, a.Td})
+	recPubkey, err := secp256k1.RecoverPubkey(crypto.Keccak256(rlp), sig)
+	if err != nil {
+		return err
+	}
+	pbytes := elliptic.Marshal(pubKey.Curve, pubKey.X, pubKey.Y)
+	if bytes.Equal(pbytes, recPubkey) {
+		return nil
+	} else {
+		return errors.New("Wrong signature")
+	}
+}
+
 type blockInfo struct {
 	Hash   common.Hash // Hash of one particular block being announced
 	Number uint64      // Number of one particular block being announced

les/server.go

@@ -18,6 +18,7 @@
 package les
 
 import (
+	"crypto/ecdsa"
 	"encoding/binary"
 	"math"
 	"sync"
@@ -41,6 +42,7 @@ type LesServer struct {
 	fcCostStats     *requestCostStats
 	defParams       *flowcontrol.ServerParams
 	lesTopics       []discv5.Topic
+	privateKey      *ecdsa.PrivateKey
 	quitSync        chan struct{}
 
 	chtIndexer, bltIndexer *core.ChainIndexer
@@ -52,7 +54,6 @@ func NewLesServer(eth *eth.Ethereum, config *eth.Config) (*LesServer, error) {
 	if err != nil {
 		return nil, err
 	}
-	pm.blockLoop()
 
 	lesTopics := make([]discv5.Topic, len(ServerProtocolVersions))
 	for i, pv := range ServerProtocolVersions {
@@ -95,6 +96,8 @@ func (s *LesServer) Start(srvr *p2p.Server) {
 			srvr.DiscV5.RegisterTopic(topic, s.quitSync)
 		}()
 	}
+	s.privateKey = srvr.PrivateKey
+	s.protocolManager.blockLoop()
 }
 
 func (s *LesServer) SetBloomBitsIndexer(bbIndexer *core.ChainIndexer) {
@@ -313,12 +316,34 @@ func (pm *ProtocolManager) blockLoop() {
 						log.Debug("Announcing block to peers", "number", number, "hash", hash, "td", td, "reorg", reorg)
 
 						announce := announceData{Hash: hash, Number: number, Td: td, ReorgDepth: reorg}
+						var (
+							signed         bool
+							signedAnnounce announceData
+						)
+
 						for _, p := range peers {
+							switch p.announceType {
+
+							case announceTypeSimple:
 								select {
 								case p.announceChn <- announce:
 								default:
 									pm.removePeer(p.id)
 								}
+
+							case announceTypeSigned:
+								if !signed {
+									signedAnnounce = announce
+									signedAnnounce.sign(pm.server.privateKey)
+									signed = true
+								}
+
+								select {
+								case p.announceChn <- signedAnnounce:
+								default:
+									pm.removePeer(p.id)
+								}
+							}
 						}
 					}
 				}