diff --git a/core/types.go b/core/types.go
index b6767c8..b8dd677 100644
--- a/core/types.go
+++ b/core/types.go
@@ -1,10 +1,10 @@
 package core
 
 import (
-	"strings"
 	"bytes"
-	"fmt"
 	"encoding/hex"
+	"fmt"
+	"strings"
 )
 
 type Hash [32]byte
@@ -15,7 +15,10 @@ func (h Hash) MarshalJSON() ([]byte, error) {
 
 func (h *Hash) UnmarshalJSON(data []byte) error {
 	d := bytes.TrimPrefix(bytes.Trim(data, `"`), []byte("0x"))
-	_, err := hex.Decode(h[(64 - len(d)) / 2:], d)
+	if len(d) > 64 {
+		return fmt.Errorf("argument of invalid length")
+	}
+	_, err := hex.Decode(h[(64-len(d))/2:], d)
 	return err
 }
 
@@ -30,7 +33,7 @@ func (h Hash) String() string {
 func HexToHash(data string) Hash {
 	h := Hash{}
 	b, _ := hex.DecodeString(strings.TrimPrefix(strings.Trim(data, `"`), "0x"))
-	copy(h[32 - len(b):], b)
+	copy(h[32-len(b):], b)
 	return h
 }
 
@@ -48,7 +51,10 @@ func (h Address) MarshalJSON() ([]byte, error) {
 
 func (h *Address) UnmarshalJSON(data []byte) error {
 	d := bytes.TrimPrefix(bytes.Trim(data, `"`), []byte("0x"))
-	_, err := hex.Decode(h[(40 - len(d))/2:], d)
+	if len(d) > 40 {
+		return fmt.Errorf("argument of invalid length")
+	}
+	_, err := hex.Decode(h[(40-len(d))/2:], d)
 	return err
 }
 
@@ -56,11 +62,10 @@ func (h Address) String() string {
 	return fmt.Sprintf("%#x", h[:])
 }
 
-
 func HexToAddress(data string) Address {
 	h := Address{}
 	b, _ := hex.DecodeString(strings.TrimPrefix(strings.Trim(data, `"`), "0x"))
-	copy(h[20 - len(b):], b)
+	copy(h[20-len(b):], b)
 	return h
 }
 
@@ -70,7 +75,6 @@ func BytesToAddress(b []byte) Address {
 	return h
 }
 
-
 type ChainEvent struct {
 	Block []byte // RLP Encoded block
 	Hash  Hash
@@ -81,12 +85,12 @@ type ChainSideEvent struct {
 	Block []byte // RLP Encoded block
 }
 
-type ChainHeadEvent struct{
-  Block []byte // RLP Encoded block
+type ChainHeadEvent struct {
+	Block []byte // RLP Encoded block
 }
 
-type NewTxsEvent struct{
-  Txs [][]byte // []RLP encoded transaction
+type NewTxsEvent struct {
+	Txs [][]byte // []RLP encoded transaction
 }
 
 type API struct {
@@ -96,7 +100,6 @@ type API struct {
 	Public    bool
 }
 
-
 func CopyBytes(a []byte) []byte {
 	b := make([]byte, len(a))
 	copy(b[:], a[:])