/
randao.go
52 lines (46 loc) · 1.87 KB
/
randao.go
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package helpers
import (
"github.com/prysmaticlabs/prysm/v4/beacon-chain/state"
"github.com/prysmaticlabs/prysm/v4/config/params"
"github.com/prysmaticlabs/prysm/v4/consensus-types/primitives"
"github.com/prysmaticlabs/prysm/v4/crypto/bls"
"github.com/prysmaticlabs/prysm/v4/crypto/hash"
"github.com/prysmaticlabs/prysm/v4/encoding/bytesutil"
)
// Seed returns the randao seed used for shuffling of a given epoch.
//
// Spec pseudocode definition:
//
// def get_seed(state: BeaconState, epoch: Epoch, domain_type: DomainType) -> Bytes32:
// """
// Return the seed at ``epoch``.
// """
// mix = get_randao_mix(state, Epoch(epoch + EPOCHS_PER_HISTORICAL_VECTOR - MIN_SEED_LOOKAHEAD - 1)) # Avoid underflow
// return hash(domain_type + uint_to_bytes(epoch) + mix)
func Seed(state state.ReadOnlyBeaconState, epoch primitives.Epoch, domain [bls.DomainByteLength]byte) ([32]byte, error) {
// See https://github.com/ethereum/consensus-specs/pull/1296 for
// rationale on why offset has to look down by 1.
lookAheadEpoch := epoch + params.BeaconConfig().EpochsPerHistoricalVector -
params.BeaconConfig().MinSeedLookahead - 1
randaoMix, err := RandaoMix(state, lookAheadEpoch)
if err != nil {
return [32]byte{}, err
}
seed := append(domain[:], bytesutil.Bytes8(uint64(epoch))...)
seed = append(seed, randaoMix...)
seed32 := hash.Hash(seed)
return seed32, nil
}
// RandaoMix returns the randao mix (xor'ed seed)
// of a given slot. It is used to shuffle validators.
//
// Spec pseudocode definition:
//
// def get_randao_mix(state: BeaconState, epoch: Epoch) -> Bytes32:
// """
// Return the randao mix at a recent ``epoch``.
// """
// return state.randao_mixes[epoch % EPOCHS_PER_HISTORICAL_VECTOR]
func RandaoMix(state state.ReadOnlyBeaconState, epoch primitives.Epoch) ([]byte, error) {
return state.RandaoMixAtIndex(uint64(epoch % params.BeaconConfig().EpochsPerHistoricalVector))
}