update to use VRF digest appropriately and simplify drawing rand past genesis

chain/store/store.go

@@ -890,12 +890,12 @@ func (cs *ChainStore) TryFillTipSet(ts *types.TipSet) (*FullTipSet, error) {
 }
 
 func drawRandomness(t *types.Ticket, pers crypto.DomainSeparationTag, round int64, entropy []byte) ([]byte, error) {
-	// TODO: Make this spec compliant
 	h := blake2b.New256()
 	if err := binary.Write(h, binary.BigEndian, int64(pers)); err != nil {
 		return nil, xerrors.Errorf("deriving randomness: %w", err)
 	}
-	h.Write(t.VRFProof)
+	VRFDigest := blake2b.Sum256(t.VRFProof)
+	h.Write(VRFDigest[:])
 	if err := binary.Write(h, binary.BigEndian, round); err != nil {
 		return nil, xerrors.Errorf("deriving randomness: %w", err)
 	}
@@ -921,25 +921,12 @@ func (cs *ChainStore) GetRandomness(ctx context.Context, blks []cid.Cid, pers cr
 
 		mtb := nts.MinTicketBlock()
 
-		if int64(nts.Height()) <= round {
+		// if at (or just past -- for null epochs) appropriate epoch
+		// or at genesis (works for negative epochs)
+		if int64(nts.Height()) <= round || mtb.Height == 0 {
 			return drawRandomness(nts.MinTicketBlock().Ticket, pers, round, entropy)
 		}
 
-		// special case for lookback behind genesis block
-		// TODO(spec): this is not in the spec, need to sync that
-		if mtb.Height == 0 {
-
-			// round is negative
-			thash, err := drawRandomness(mtb.Ticket, pers, round*-1, entropy)
-			if err != nil {
-				return nil, err
-			}
-
-			// for negative lookbacks, just use the hash of the positive tickethash value
-			h := blake2b.Sum256(thash)
-			return h[:], nil
-		}
-
 		blks = mtb.Parents
 	}
 }

chain/types/blockheader.go

@@ -9,6 +9,7 @@ import (
 
 	block "github.com/ipfs/go-block-format"
 	"github.com/ipfs/go-cid"
+	"github.com/minio/blake2b-simd"
 	"github.com/minio/sha256-simd"
 	"github.com/multiformats/go-multihash"
 	xerrors "golang.org/x/xerrors"
@@ -214,5 +215,7 @@ func ElectionPostChallengeCount(sectors uint64, faults uint64) uint64 {
 }
 
 func (t *Ticket) Equals(ot *Ticket) bool {
-	return bytes.Equal(t.VRFProof, ot.VRFProof)
+	tDigest := blake2b.Sum256(t.VRFProof)
+	otDigest := blake2b.Sum256(ot.VRFProof)
+	return bytes.Equal(tDigest[:], otDigest[:])
 }

chain/types/tipset.go

@@ -10,6 +10,7 @@ import (
 	"github.com/filecoin-project/specs-actors/actors/abi"
 	"github.com/ipfs/go-cid"
 	logging "github.com/ipfs/go-log/v2"
+	"github.com/minio/blake2b-simd"
 	cbg "github.com/whyrusleeping/cbor-gen"
 	"golang.org/x/xerrors"
 )
@@ -170,7 +171,9 @@ func (ts *TipSet) Equals(ots *TipSet) bool {
 }
 
 func (t *Ticket) Less(o *Ticket) bool {
-	return bytes.Compare(t.VRFProof, o.VRFProof) < 0
+	tDigest := blake2b.Sum256(t.VRFProof)
+	oDigest := blake2b.Sum256(o.VRFProof)
+	return bytes.Compare(tDigest[:], oDigest[:]) < 0
 }
 
 func (ts *TipSet) MinTicket() *Ticket {