Validate Aggregator hash from the validator set (#822)

When validating the Signed Header in Validate Basic we should check if
the aggregator hash corresponds to the hash of the validator set.

Closes: #820

Author: Manav-Aggarwal

types/validation.go

@@ -1,6 +1,7 @@
 package types
 
 import (
+	"bytes"
 	"errors"
 
 	"github.com/tendermint/tendermint/crypto/ed25519"
@@ -61,6 +62,10 @@ func (h *SignedHeader) ValidateBasic() error {
 		return err
 	}
 
+	if !bytes.Equal(h.Validators.Hash(), h.AggregatorsHash[:]) {
+		return errors.New("aggregator set hash in signed header and hash of validator set do not match")
+	}
+
 	// Make sure there is exactly one signature
 	if len(h.Commit.Signatures) != 1 {
 		return errors.New("expected exactly one signature")