Bring back the 2/3f+1 threshold for multi-sig and add basic response check

consensus/consensus_leader.go

@@ -4,6 +4,7 @@ import (
 	"bytes"
 	"encoding/binary"
 	"encoding/gob"
+	"errors"
 	"time"
 
 	"github.com/dedis/kyber"
@@ -152,7 +153,7 @@ func (consensus *Consensus) processCommitMessage(payload []byte) {
 		return
 	}
 
-	if len(consensus.commitments) >= len(consensus.validators)+1 && consensus.state < CHALLENGE_DONE {
+	if len(consensus.commitments) >= (2*len(consensus.publicKeys)/3)+1 && consensus.state < CHALLENGE_DONE {
 		consensus.Log.Debug("Enough commitments received with signatures", "num", len(consensus.commitments))
 
 		// Broadcast challenge
@@ -230,12 +231,20 @@ func (consensus *Consensus) processResponseMessage(payload []byte) {
 	_, ok = consensus.responses[validatorId]
 	shouldProcess = shouldProcess && !ok
 	if shouldProcess {
-		scalar := crypto.Ed25519Curve.Scalar()
-		scalar.UnmarshalBinary(response)
-		consensus.responses[validatorId] = scalar
+		// verify the response matches the received commit
+		responseScalar := crypto.Ed25519Curve.Scalar()
+		responseScalar.UnmarshalBinary(response)
+		err := consensus.verifyResponse(responseScalar, validatorId)
+		if err != nil {
+			consensus.Log.Warn("Failed to verify the response", "error", err)
+			shouldProcess = false
+		} else {
+			consensus.responses[validatorId] = responseScalar
 			// Set the bitmap indicate this validate signed. TODO: figure out how to resolve the inconsistency of validators from commit and response messages
 			consensus.bitmap.SetKey(value.PubKey, true)
 		}
+
+	}
 	consensus.mutex.Unlock()
 
 	if !shouldProcess {
@@ -243,9 +252,9 @@ func (consensus *Consensus) processResponseMessage(payload []byte) {
 	}
 
 	//consensus.Log.Debug("RECEIVED RESPONSE", "consensusId", consensusId)
-	if len(consensus.responses) >= len(consensus.validators)+1 && consensus.state != FINISHED {
+	if len(consensus.responses) >= (2*len(consensus.publicKeys)/3)+1 && consensus.state != FINISHED {
 		consensus.mutex.Lock()
-		if len(consensus.responses) >= len(consensus.validators)+1 && consensus.state != FINISHED {
+		if len(consensus.responses) >= (2*len(consensus.publicKeys)/3)+1 && consensus.state != FINISHED {
 			consensus.Log.Debug("Enough responses received with signatures", "num", len(consensus.responses))
 			// Aggregate responses
 			responses := []kyber.Scalar{}
@@ -317,3 +326,26 @@ func (consensus *Consensus) processResponseMessage(payload []byte) {
 		consensus.mutex.Unlock()
 	}
 }
+
+func (consensus *Consensus) verifyResponse(response kyber.Scalar, validatorId uint16) error {
+	if response.Equal(crypto.Ed25519Curve.Scalar()) {
+		return errors.New("response is zero valued")
+	}
+	_, ok := consensus.commitments[validatorId]
+	if !ok {
+		return errors.New("no commit is received for the validator")
+	}
+	// TODO(RJ): enable the actual check
+	//challenge := crypto.Ed25519Curve.Scalar()
+	//challenge.UnmarshalBinary(consensus.challenge[:])
+	//
+	//// compute Q = sG + r*pubKey
+	//sG := crypto.Ed25519Curve.Point().Mul(response, nil)
+	//r_pubKey := crypto.Ed25519Curve.Point().Mul(challenge, consensus.validators[validatorId].PubKey)
+	//Q := crypto.Ed25519Curve.Point().Add(sG, r_pubKey)
+	//
+	//if !Q.Equal(commit) {
+	//	return errors.New("recreated commit doesn't match the received one")
+	//}
+	return nil
+}

consensus/consensus_validator.go

@@ -325,7 +325,7 @@ func (consensus *Consensus) processCollectiveSigMessage(payload []byte) {
 	}
 
 	// Verify collective signature
-	err := crypto.Verify(crypto.Ed25519Curve, consensus.publicKeys, payload[:36], append(collectiveSig, bitmap...), crypto.NewThresholdPolicy(len(consensus.publicKeys)/2))
+	err := crypto.Verify(crypto.Ed25519Curve, consensus.publicKeys, payload[:36], append(collectiveSig, bitmap...), crypto.NewThresholdPolicy((2*len(consensus.publicKeys)/3)+1))
 	if err != nil {
 		consensus.Log.Warn("Failed to verify the collective sig message", "consensusId", consensusId, "err", err)
 	}