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attestation.go
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attestation.go
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package helpers
import (
"encoding/binary"
"github.com/pkg/errors"
ethpb "github.com/prysmaticlabs/ethereumapis/eth/v1alpha1"
stateTrie "github.com/prysmaticlabs/prysm/beacon-chain/state"
"github.com/prysmaticlabs/prysm/shared/bls"
"github.com/prysmaticlabs/prysm/shared/hashutil"
"github.com/prysmaticlabs/prysm/shared/params"
)
var (
// ErrAttestationAggregationBitsOverlap is returned when two attestations aggregation
// bits overlap with each other.
ErrAttestationAggregationBitsOverlap = errors.New("overlapping aggregation bits")
// ErrAttestationAggregationBitsDifferentLen is returned when two attestation aggregation bits
// have different lengths.
ErrAttestationAggregationBitsDifferentLen = errors.New("different bitlist lengths")
)
// AggregateAttestations such that the minimal number of attestations are returned.
// Note: this is currently a naive implementation to the order of O(n^2).
func AggregateAttestations(atts []*ethpb.Attestation) ([]*ethpb.Attestation, error) {
if len(atts) <= 1 {
return atts, nil
}
// Naive aggregation. O(n^2) time.
for i, a := range atts {
if i >= len(atts) {
break
}
for j := i + 1; j < len(atts); j++ {
b := atts[j]
if a.AggregationBits.Len() == b.AggregationBits.Len() && !a.AggregationBits.Overlaps(b.AggregationBits) {
var err error
a, err = AggregateAttestation(a, b)
if err != nil {
return nil, err
}
// Delete b
atts = append(atts[:j], atts[j+1:]...)
j--
atts[i] = a
}
}
}
// Naive deduplication of identical aggregations. O(n^2) time.
for i, a := range atts {
for j := i + 1; j < len(atts); j++ {
b := atts[j]
if a.AggregationBits.Len() != b.AggregationBits.Len() {
continue
}
if a.AggregationBits.Contains(b.AggregationBits) {
// If b is fully contained in a, then b can be removed.
atts = append(atts[:j], atts[j+1:]...)
j--
} else if b.AggregationBits.Contains(a.AggregationBits) {
// if a is fully contained in b, then a can be removed.
atts = append(atts[:i], atts[i+1:]...)
i--
break // Stop the inner loop, advance a.
}
}
}
return atts, nil
}
// BLS aggregate signature aliases for testing / benchmark substitution. These methods are
// significantly more expensive than the inner logic of AggregateAttestations so they must be
// substituted for benchmarks which analyze AggregateAttestations.
var aggregateSignatures = bls.AggregateSignatures
var signatureFromBytes = bls.SignatureFromBytes
// AggregateAttestation aggregates attestations a1 and a2 together.
func AggregateAttestation(a1 *ethpb.Attestation, a2 *ethpb.Attestation) (*ethpb.Attestation, error) {
if a1.AggregationBits.Len() != a2.AggregationBits.Len() {
return nil, ErrAttestationAggregationBitsDifferentLen
}
if a1.AggregationBits.Overlaps(a2.AggregationBits) {
return nil, ErrAttestationAggregationBitsOverlap
}
baseAtt := stateTrie.CopyAttestation(a1)
newAtt := stateTrie.CopyAttestation(a2)
if newAtt.AggregationBits.Count() > baseAtt.AggregationBits.Count() {
baseAtt, newAtt = newAtt, baseAtt
}
if baseAtt.AggregationBits.Contains(newAtt.AggregationBits) {
return baseAtt, nil
}
newBits := baseAtt.AggregationBits.Or(newAtt.AggregationBits)
newSig, err := signatureFromBytes(newAtt.Signature)
if err != nil {
return nil, err
}
baseSig, err := signatureFromBytes(baseAtt.Signature)
if err != nil {
return nil, err
}
aggregatedSig := aggregateSignatures([]*bls.Signature{baseSig, newSig})
baseAtt.Signature = aggregatedSig.Marshal()
baseAtt.AggregationBits = newBits
return baseAtt, nil
}
// SlotSignature returns the signed signature of the hash tree root of input slot.
//
// Spec pseudocode definition:
// def get_slot_signature(state: BeaconState, slot: Slot, privkey: int) -> BLSSignature:
// domain = get_domain(state, DOMAIN_BEACON_ATTESTER, compute_epoch_at_slot(slot))
// return bls_sign(privkey, hash_tree_root(slot), domain)
func SlotSignature(state *stateTrie.BeaconState, slot uint64, privKey *bls.SecretKey) (*bls.Signature, error) {
d, err := Domain(state.Fork(), CurrentEpoch(state), params.BeaconConfig().DomainBeaconAttester, state.GenesisValidatorRoot())
if err != nil {
return nil, err
}
s, err := ComputeSigningRoot(slot, d)
if err != nil {
return nil, err
}
return privKey.Sign(s[:]), nil
}
// IsAggregator returns true if the signature is from the input validator. The committee
// count is provided as an argument rather than direct implementation from spec. Having
// committee count as an argument allows cheaper computation at run time.
//
// Spec pseudocode definition:
// def is_aggregator(state: BeaconState, slot: Slot, index: CommitteeIndex, slot_signature: BLSSignature) -> bool:
// committee = get_beacon_committee(state, slot, index)
// modulo = max(1, len(committee) // TARGET_AGGREGATORS_PER_COMMITTEE)
// return bytes_to_int(hash(slot_signature)[0:8]) % modulo == 0
func IsAggregator(committeeCount uint64, slotSig []byte) (bool, error) {
modulo := uint64(1)
if committeeCount/params.BeaconConfig().TargetAggregatorsPerCommittee > 1 {
modulo = committeeCount / params.BeaconConfig().TargetAggregatorsPerCommittee
}
b := hashutil.Hash(slotSig)
return binary.LittleEndian.Uint64(b[:8])%modulo == 0, nil
}
// AggregateSignature returns the aggregated signature of the input attestations.
//
// Spec pseudocode definition:
// def get_aggregate_signature(attestations: Sequence[Attestation]) -> BLSSignature:
// signatures = [attestation.signature for attestation in attestations]
// return bls_aggregate_signatures(signatures)
func AggregateSignature(attestations []*ethpb.Attestation) (*bls.Signature, error) {
sigs := make([]*bls.Signature, len(attestations))
var err error
for i := 0; i < len(sigs); i++ {
sigs[i], err = signatureFromBytes(attestations[i].Signature)
if err != nil {
return nil, err
}
}
return aggregateSignatures(sigs), nil
}
// IsAggregated returns true if the attestation is an aggregated attestation,
// false otherwise.
func IsAggregated(attestation *ethpb.Attestation) bool {
return attestation.AggregationBits.Count() > 1
}