Simplex QuorumCertificate and BLS aggregator

simplex/quorum.go

@@ -0,0 +1,183 @@
+// Copyright (C) 2019-2024, Ava Labs, Inc. All rights reserved.
+// See the file LICENSE for licensing terms.
+
+package simplex
+
+import (
+	"encoding/asn1"
+	"errors"
+	"fmt"
+
+	"github.com/ava-labs/simplex"
+
+	"github.com/ava-labs/avalanchego/ids"
+	"github.com/ava-labs/avalanchego/utils/crypto/bls"
+)
+
+var (
+	_ simplex.QuorumCertificate   = (*QC)(nil)
+	_ simplex.QCDeserializer      = QCDeserializer{}
+	_ simplex.SignatureAggregator = (*SignatureAggregator)(nil)
+
+	// QC errors
+	errFailedToParseQC       = errors.New("failed to parse quorum certificate")
+	errUnexpectedSigners     = errors.New("unexpected number of signers in quorum certificate")
+	errSignatureAggregation  = errors.New("signature aggregation failed")
+	errEncodingMessageToSign = errors.New("failed to encode message to sign")
+)
+
+// QC represents a quorum certificate in the Simplex consensus protocol.
+type QC struct {
+	verifier BLSVerifier
+	sig      bls.Signature
+	signers  []simplex.NodeID
+}
+
+// Signers returns the list of signers for the quorum certificate.
+func (qc *QC) Signers() []simplex.NodeID {
+	return qc.signers
+}
+
+// Verify checks if the quorum certificate is valid by verifying the aggregated signature against the signers' public keys.
+func (qc *QC) Verify(msg []byte) error {
+	pks := make([]*bls.PublicKey, 0, len(qc.signers))
+	if len(qc.signers) != simplex.Quorum(len(qc.verifier.nodeID2PK)) {
+		return fmt.Errorf("%w: expected %d signers but got %d", errUnexpectedSigners, simplex.Quorum(len(qc.verifier.nodeID2PK)), len(qc.signers))
+	}
+
+	// ensure all signers are in the membership set
+	for _, signer := range qc.signers {
+		pk, exists := qc.verifier.nodeID2PK[ids.NodeID(signer)]
+		if !exists {
+			return fmt.Errorf("%w: %x", errSignerNotFound, signer)
+		}
+
+		pks = append(pks, pk)
+	}
+
+	// aggregate the public keys
+	aggPK, err := bls.AggregatePublicKeys(pks)
+	if err != nil {
+		return fmt.Errorf("%w: %w", errSignatureAggregation, err)
+	}
+
+	message2Verify, err := encodeMessageToSign(msg, qc.verifier.chainID, qc.verifier.networkID)
+	if err != nil {
+		return fmt.Errorf("%w: %w", errEncodingMessageToSign, err)
+	}
+
+	if !bls.Verify(aggPK, &qc.sig, message2Verify) {
+		return errSignatureVerificationFailed
+	}
+
+	return nil
+}
+
+// asn1QC is the ASN.1 structure for the quorum certificate.
+// It contains the signers' public keys and the aggregated signature.
+// The signers are represented as byte slices of their IDs.
+type asn1QC struct {
+	Signers   [][]byte
+	Signature []byte
+}
+
+func (qc *QC) MarshalASN1() ([]byte, error) {
+	sigBytes := bls.SignatureToBytes(&qc.sig)
+
+	signersBytes := make([][]byte, len(qc.signers))
+	for i, signer := range qc.signers {
+		s := signer // avoid aliasing
+		signersBytes[i] = s[:]
+	}
+	asn1Data := asn1QC{
+		Signers:   signersBytes,
+		Signature: sigBytes,
+	}
+	return asn1.Marshal(asn1Data)
+}
+
+func (qc *QC) UnmarshalASN1(data []byte) error {
+	var decoded asn1QC
+	_, err := asn1.Unmarshal(data, &decoded)
+	if err != nil {
+		return err
+	}
+	qc.signers = make([]simplex.NodeID, len(decoded.Signers))
+	for i, signerBytes := range decoded.Signers {
+		if len(signerBytes) != ids.ShortIDLen { // TODO: so long as simplex is in a separate repo, we should decouple these ids as much as possible
+			return errors.New("invalid signer length")
+		}
+		qc.signers[i] = simplex.NodeID(signerBytes)
+	}
+	sig, err := bls.SignatureFromBytes(decoded.Signature)
+	if err != nil {
+		return err
+	}
+	qc.sig = *sig
+
+	return nil
+}
+
+// Bytes serializes the quorum certificate into bytes.
+func (qc *QC) Bytes() []byte {
+	bytes, err := qc.MarshalASN1()
+	if err != nil {
+		panic(fmt.Errorf("failed to marshal QC: %w", err))
+	}
+	return bytes
+}
+
+type QCDeserializer BLSVerifier
+
+// DeserializeQuorumCertificate deserializes a quorum certificate from bytes.
+func (d QCDeserializer) DeserializeQuorumCertificate(bytes []byte) (simplex.QuorumCertificate, error) {
+	var qc QC
+	if err := qc.UnmarshalASN1(bytes); err != nil {
+		return nil, fmt.Errorf("%w: %w", errFailedToParseQC, err)
+	}
+	qc.verifier = BLSVerifier(d)
+
+	return &qc, nil
+}
+
+// SignatureAggregator aggregates signatures into a quorum certificate.
+type SignatureAggregator BLSVerifier
+
+// Aggregate aggregates the provided signatures into a quorum certificate.
+// It requires at least a quorum of signatures to succeed.
+// If any signature is from a signer not in the membership set, it returns an error.
+func (a SignatureAggregator) Aggregate(signatures []simplex.Signature) (simplex.QuorumCertificate, error) {
+	quorumSize := simplex.Quorum(len(a.nodeID2PK))
+	if len(signatures) < quorumSize {
+		return nil, fmt.Errorf("%w: expected %d signatures but got %d", errUnexpectedSigners, quorumSize, len(signatures))
+	}
+
+	signatures = signatures[:quorumSize]
+
+	signers := make([]simplex.NodeID, 0, quorumSize)
+	sigs := make([]*bls.Signature, 0, quorumSize)
+	for _, signature := range signatures {
+		signer := signature.Signer
+		_, exists := a.nodeID2PK[ids.NodeID(signer)]
+		if !exists {
+			return nil, fmt.Errorf("%w: %x", errSignerNotFound, signer)
+		}
+		signers = append(signers, signer)
+		sig, err := bls.SignatureFromBytes(signature.Value)
+		if err != nil {
+			return nil, fmt.Errorf("%w: %w", errFailedToParseSignature, err)
+		}
+		sigs = append(sigs, sig)
+	}
+
+	aggregatedSig, err := bls.AggregateSignatures(sigs)
+	if err != nil {
+		return nil, fmt.Errorf("%w: %w", errSignatureAggregation, err)
+	}
+
+	return &QC{
+		verifier: BLSVerifier(a),
+		signers:  signers,
+		sig:      *aggregatedSig,
+	}, nil
+}