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combined_vote_processor_v3.go
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combined_vote_processor_v3.go
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package votecollector
import (
"errors"
"fmt"
"github.com/onflow/crypto"
"github.com/rs/zerolog"
"go.uber.org/atomic"
"github.com/onflow/flow-go/consensus/hotstuff"
"github.com/onflow/flow-go/consensus/hotstuff/model"
"github.com/onflow/flow-go/consensus/hotstuff/signature"
"github.com/onflow/flow-go/consensus/hotstuff/verification"
"github.com/onflow/flow-go/model/encoding"
"github.com/onflow/flow-go/model/flow"
msig "github.com/onflow/flow-go/module/signature"
)
/* **************** Base-Factory for CombinedVoteProcessors ***************** */
// combinedVoteProcessorFactoryBaseV3 is a `votecollector.baseFactory` for creating
// CombinedVoteProcessors, holding all needed dependencies.
// combinedVoteProcessorFactoryBaseV3 is intended to be used for the main consensus.
// CAUTION:
// this base factory only creates the VerifyingVoteProcessor for the given block.
// It does _not_ check the proposer's vote for its own block, i.e. it does _not_
// implement `hotstuff.VoteProcessorFactory`. This base factory should be wrapped
// by `votecollector.VoteProcessorFactory` which adds the logic to verify
// the proposer's vote (decorator pattern).
// nolint:unused
type combinedVoteProcessorFactoryBaseV3 struct {
committee hotstuff.DynamicCommittee
onQCCreated hotstuff.OnQCCreated
packer hotstuff.Packer
}
// Create creates CombinedVoteProcessorV3 for processing votes for the given block.
// Caller must treat all errors as exceptions
// nolint:unused
func (f *combinedVoteProcessorFactoryBaseV3) Create(log zerolog.Logger, block *model.Block) (hotstuff.VerifyingVoteProcessor, error) {
allParticipants, err := f.committee.IdentitiesByBlock(block.BlockID)
if err != nil {
return nil, fmt.Errorf("error retrieving consensus participants at block %v: %w", block.BlockID, err)
}
// message that has to be verified against aggregated signature
msg := verification.MakeVoteMessage(block.View, block.BlockID)
// prepare the staking public keys of participants
stakingKeys := make([]crypto.PublicKey, 0, len(allParticipants))
for _, participant := range allParticipants {
stakingKeys = append(stakingKeys, participant.StakingPubKey)
}
stakingSigAggtor, err := signature.NewWeightedSignatureAggregator(allParticipants, stakingKeys, msg, msig.ConsensusVoteTag)
if err != nil {
return nil, fmt.Errorf("could not create aggregator for staking signatures: %w", err)
}
dkg, err := f.committee.DKG(block.View)
if err != nil {
return nil, fmt.Errorf("could not get DKG info at block %v: %w", block.BlockID, err)
}
// prepare the random beacon public keys of participants
beaconKeys := make([]crypto.PublicKey, 0, len(allParticipants))
for _, participant := range allParticipants {
pk, err := dkg.KeyShare(participant.NodeID)
if err != nil {
return nil, fmt.Errorf("could not get random beacon key share for %x: %w", participant.NodeID, err)
}
beaconKeys = append(beaconKeys, pk)
}
rbSigAggtor, err := signature.NewWeightedSignatureAggregator(allParticipants, beaconKeys, msg, msig.RandomBeaconTag)
if err != nil {
return nil, fmt.Errorf("could not create aggregator for thershold signatures: %w", err)
}
threshold := msig.RandomBeaconThreshold(int(dkg.Size()))
randomBeaconInspector, err := signature.NewRandomBeaconInspector(dkg.GroupKey(), beaconKeys, threshold, msg)
if err != nil {
return nil, fmt.Errorf("could not create random beacon inspector: %w", err)
}
rbRector := signature.NewRandomBeaconReconstructor(dkg, randomBeaconInspector)
minRequiredWeight, err := f.committee.QuorumThresholdForView(block.View)
if err != nil {
return nil, fmt.Errorf("could not get weight threshold for view %d: %w", block.View, err)
}
return &CombinedVoteProcessorV3{
log: log.With().Hex("block_id", block.BlockID[:]).Logger(),
block: block,
stakingSigAggtor: stakingSigAggtor,
rbSigAggtor: rbSigAggtor,
rbRector: rbRector,
onQCCreated: f.onQCCreated,
packer: f.packer,
minRequiredWeight: minRequiredWeight,
done: *atomic.NewBool(false),
}, nil
}
/* ****************** CombinedVoteProcessorV3 Implementation ****************** */
// CombinedVoteProcessorV3 implements the hotstuff.VerifyingVoteProcessor interface.
// It processes votes from the main consensus committee, where participants vote in
// favour of a block by proving either their staking key signature or their random
// beacon signature. In the former case, the participant only contributes to HotStuff
// progress; while in the latter case, the voter also contributes to running the
// random beacon. Concurrency safe.
type CombinedVoteProcessorV3 struct {
log zerolog.Logger
block *model.Block
stakingSigAggtor hotstuff.WeightedSignatureAggregator
rbSigAggtor hotstuff.WeightedSignatureAggregator
rbRector hotstuff.RandomBeaconReconstructor
onQCCreated hotstuff.OnQCCreated
packer hotstuff.Packer
minRequiredWeight uint64
done atomic.Bool
}
var _ hotstuff.VerifyingVoteProcessor = (*CombinedVoteProcessorV3)(nil)
// Block returns block that is part of proposal that we are processing votes for.
func (p *CombinedVoteProcessorV3) Block() *model.Block {
return p.block
}
// Status returns status of this vote processor, it's always verifying.
func (p *CombinedVoteProcessorV3) Status() hotstuff.VoteCollectorStatus {
return hotstuff.VoteCollectorStatusVerifying
}
// Process performs processing of single vote in concurrent safe way. This function is implemented to be
// called by multiple goroutines at the same time. Supports processing of both staking and random beacon signatures.
// Design of this function is event driven: as soon as we collect enough signatures to create a QC we will immediately do so
// and submit it via callback for further processing.
// Expected error returns during normal operations:
// * VoteForIncompatibleBlockError - submitted vote for incompatible block
// * VoteForIncompatibleViewError - submitted vote for incompatible view
// * model.InvalidVoteError - submitted vote with invalid signature
// * model.DuplicatedSignerError - vote from a signer whose vote was previously already processed
// All other errors should be treated as exceptions.
//
// CAUTION: implementation is NOT (yet) BFT
// Explanation: for correctness, we require that no voter can be counted repeatedly. However,
// CombinedVoteProcessorV3 relies on the `VoteCollector`'s `votesCache` filter out all votes but the first for
// every signerID. However, we have the edge case, where we still feed the proposers vote twice into the
// `VerifyingVoteProcessor` (once as part of a cached vote, once as an individual vote). This can be exploited
// by a byzantine proposer to be erroneously counted twice, which would lead to a safety fault.
//
// TODO (suggestion): I think it would be worth-while to include a second `votesCache` into the `CombinedVoteProcessorV3`.
// Thereby, `CombinedVoteProcessorV3` inherently guarantees correctness of the QCs it produces without relying on
// external conditions (making the code more modular, less interdependent and thereby easier to maintain). The
// runtime overhead is marginal: For `votesCache` to add 500 votes (concurrently with 20 threads) takes about
// 0.25ms. This runtime overhead is neglectable and a good tradeoff for the gain in maintainability and code clarity.
func (p *CombinedVoteProcessorV3) Process(vote *model.Vote) error {
err := EnsureVoteForBlock(vote, p.block)
if err != nil {
return fmt.Errorf("received incompatible vote %v: %w", vote.ID(), err)
}
// Vote Processing state machine
if p.done.Load() {
return nil
}
sigType, sig, err := msig.DecodeSingleSig(vote.SigData)
if err != nil {
if errors.Is(err, msig.ErrInvalidSignatureFormat) {
return model.NewInvalidVoteErrorf(vote, "could not decode signature: %w", err)
}
return fmt.Errorf("unexpected error decoding vote %v: %w", vote.ID(), err)
}
switch sigType {
case encoding.SigTypeStaking:
err := p.stakingSigAggtor.Verify(vote.SignerID, sig)
if err != nil {
if model.IsInvalidSignerError(err) {
return model.NewInvalidVoteErrorf(vote, "vote %x for view %d is not signed by an authorized consensus participant: %w",
vote.ID(), vote.View, err)
}
if errors.Is(err, model.ErrInvalidSignature) {
return model.NewInvalidVoteErrorf(vote, "vote %x for view %d has an invalid staking signature: %w",
vote.ID(), vote.View, err)
}
return fmt.Errorf("internal error checking signature validity for vote %v: %w", vote.ID(), err)
}
if p.done.Load() {
return nil
}
_, err = p.stakingSigAggtor.TrustedAdd(vote.SignerID, sig)
if err != nil {
// we don't expect any errors here during normal operation, as we previously checked
// for duplicated votes from the same signer and verified the signer+signature
return fmt.Errorf("adding the signature to staking aggregator failed for vote %v: %w", vote.ID(), err)
}
case encoding.SigTypeRandomBeacon:
err := p.rbSigAggtor.Verify(vote.SignerID, sig)
if err != nil {
if model.IsInvalidSignerError(err) {
return model.NewInvalidVoteErrorf(vote, "vote %x for view %d is not from an authorized random beacon participant: %w",
vote.ID(), vote.View, err)
}
if errors.Is(err, model.ErrInvalidSignature) {
return model.NewInvalidVoteErrorf(vote, "vote %x for view %d has an invalid random beacon signature: %w",
vote.ID(), vote.View, err)
}
return fmt.Errorf("internal error checking signature validity for vote %v: %w", vote.ID(), err)
}
if p.done.Load() {
return nil
}
// Add signatures to `rbSigAggtor` and `rbRector`: we don't expect any errors during normal operation,
// as we previously checked for duplicated votes from the same signer and verified the signer+signature
_, err = p.rbSigAggtor.TrustedAdd(vote.SignerID, sig)
if err != nil {
return fmt.Errorf("unexpected exception adding signature from vote %v to random beacon aggregator: %w", vote.ID(), err)
}
_, err = p.rbRector.TrustedAdd(vote.SignerID, sig)
if err != nil {
return fmt.Errorf("unexpected exception adding signature from vote %v to random beacon reconstructor: %w", vote.ID(), err)
}
default:
return model.NewInvalidVoteErrorf(vote, "invalid signature type %d: %w", sigType, model.NewInvalidFormatErrorf(""))
}
// checking of conditions for building QC are satisfied
if p.stakingSigAggtor.TotalWeight()+p.rbSigAggtor.TotalWeight() < p.minRequiredWeight {
return nil
}
if !p.rbRector.EnoughShares() {
return nil
}
// At this point, we have enough signatures to build a QC. Another routine
// might just be at this point. To avoid duplicate work, only one routine can pass:
if !p.done.CompareAndSwap(false, true) {
return nil
}
// Our algorithm for checking votes and adding them to the aggregators should
// guarantee that we are _always_ able to successfully construct a QC when we
// reach this point. A failure implies that the VoteProcessor's internal state is corrupted.
qc, err := p.buildQC()
if err != nil {
return fmt.Errorf("internal error constructing QC from votes: %w", err)
}
p.log.Info().
Uint64("view", qc.View).
Hex("signers", qc.SignerIndices).
Msg("new QC has been created")
p.onQCCreated(qc)
return nil
}
// buildQC performs aggregation and reconstruction of signatures when we have collected enough
// signatures for building a QC. This function is run only once by a single worker.
// Any error should be treated as exception.
func (p *CombinedVoteProcessorV3) buildQC() (*flow.QuorumCertificate, error) {
// STEP 1: aggregate staking signatures (if there are any)
// * It is possible that all replicas signed with their random beacon keys.
// Per Convention, we represent an empty set of staking signers as
// `stakingSigners` and `aggregatedStakingSig` both being zero-length
// (here, we use `nil`).
// * If it has _not collected any_ signatures, `stakingSigAggtor.Aggregate()`
// errors with a `model.InsufficientSignaturesError`. We shortcut this case,
// and only call `Aggregate`, if the `stakingSigAggtor` has collected signatures
// with non-zero weight (i.e. at least one signature was collected).
var stakingSigners []flow.Identifier // nil (zero value) represents empty set of staking signers
var aggregatedStakingSig []byte // nil (zero value) for empty set of staking signers
if p.stakingSigAggtor.TotalWeight() > 0 {
var err error
stakingSigners, aggregatedStakingSig, err = p.stakingSigAggtor.Aggregate()
if err != nil {
return nil, fmt.Errorf("unexpected error aggregating staking signatures: %w", err)
}
}
// STEP 2: reconstruct random beacon group sig and aggregate random beacon sig shares
// Note: A valid random beacon group sig is required for QC validity. Our logic guarantees
// that we always collect the minimally required number (non-zero) of signature shares.
beaconSigners, aggregatedRandomBeaconSig, err := p.rbSigAggtor.Aggregate()
if err != nil {
return nil, fmt.Errorf("could not aggregate random beacon signatures: %w", err)
}
reconstructedBeaconSig, err := p.rbRector.Reconstruct()
if err != nil {
return nil, fmt.Errorf("could not reconstruct random beacon group signature: %w", err)
}
// STEP 3: generate BlockSignatureData and serialize it
blockSigData := &hotstuff.BlockSignatureData{
StakingSigners: stakingSigners,
RandomBeaconSigners: beaconSigners,
AggregatedStakingSig: aggregatedStakingSig,
AggregatedRandomBeaconSig: aggregatedRandomBeaconSig,
ReconstructedRandomBeaconSig: reconstructedBeaconSig,
}
signerIndices, sigData, err := p.packer.Pack(p.block.View, blockSigData)
if err != nil {
return nil, fmt.Errorf("could not pack the block sig data: %w", err)
}
return &flow.QuorumCertificate{
View: p.block.View,
BlockID: p.block.BlockID,
SignerIndices: signerIndices,
SigData: sigData,
}, nil
}