core, dex: use block hash as witness data (#160)

Using only state root and receipt root as witness data can not protect
other fields in block header, ex: bloom, difficulty, gas limit, gas
used...
So that everyone can manipulate these fields to create as many valid blocks
at the same height as he want. Although this will not effect the state,
one can spam us when syncing.

Using block hash as witness data can solve this.

1 files changed, 5 insertions, 9 deletions

diff --git a/core/block_validator.go b/core/block_validator.go
index c6038381f..f42ea6b11 100644
--- a/core/block_validator.go
+++ b/core/block_validator.go
@@ -19,6 +19,7 @@ package core
 import (
 	"fmt"
 
+	"github.com/dexon-foundation/dexon/common"
 	"github.com/dexon-foundation/dexon/consensus"
 	"github.com/dexon-foundation/dexon/core/state"
 	"github.com/dexon-foundation/dexon/core/types"
@@ -101,20 +102,15 @@ func (v *BlockValidator) ValidateState(block, parent *types.Block, statedb *stat
 	return nil
 }
 
-func (v *BlockValidator) ValidateWitnessData(height uint64, data types.WitnessData) error {
+func (v *BlockValidator) ValidateWitnessData(height uint64, blockHash common.Hash) error {
 	b := v.bc.GetBlockByNumber(height)
 	if b == nil {
 		return fmt.Errorf("can not find block %v either pending or confirmed block", height)
 	}
 
-	if b.Root() != data.Root {
-		return fmt.Errorf("invalid witness root %s vs %s",
-			b.Root().String(), data.Root.String())
-	}
-
-	if b.ReceiptHash() != data.ReceiptHash {
-		return fmt.Errorf("invalid witness receipt hash %s vs %s",
-			b.ReceiptHash().String(), data.ReceiptHash.String())
+	if b.Hash() != blockHash {
+		return fmt.Errorf("invalid witness block %s vs %s",
+			b.Hash().String(), blockHash.String())
 	}
 	return nil
 }