diff --git a/core/transaction.go b/core/transaction.go
index 843efcc..db44f62 100644
--- a/core/transaction.go
+++ b/core/transaction.go
@@ -53,20 +53,21 @@ func NewTransaction(data []byte) *Transaction {
 }
 
 func (tx *Transaction) Hash(hasher Hasher[*Transaction]) types.Hash {
+	hash := hasher.Hash(tx)
 	if tx.hash.IsZero() {
-		tx.hash = hasher.Hash(tx)
+		tx.hash = hash
 	}
-	return tx.hash
+	return hash
 }
 
 func (tx *Transaction) Sign(privKey crypto.PrivateKey) error {
+	tx.From = privKey.PublicKey()
 	hash := tx.Hash(TxHasher{})
 	sig, err := privKey.Sign(hash.ToSlice())
 	if err != nil {
 		return err
 	}
 
-	tx.From = privKey.PublicKey()
 	tx.Signature = sig
 
 	return nil
diff --git a/core/transaction_test.go b/core/transaction_test.go
index 6576851..225cbb7 100644
--- a/core/transaction_test.go
+++ b/core/transaction_test.go
@@ -106,3 +106,18 @@ func randomTxWithSignature(t *testing.T) *Transaction {
 
 	return &tx
 }
+
+func TestTemperTxData(t *testing.T) {
+	userA := crypto.GeneratePrivateKey()
+	userB := crypto.GeneratePrivateKey()
+	tx := &Transaction{
+		From:  userA.PublicKey(),
+		To:    userB.PublicKey(),
+		Value: 666,
+		Data:  []byte("user a send 666 to user b"),
+	}
+	assert.Nil(t, tx.Sign(userA))
+	assert.Nil(t, tx.Verify())
+	tx.Data = []byte("hhh")
+	assert.NotNil(t, tx.Verify())
+}
diff --git a/network/tcp_transport.go b/network/tcp_transport.go
index 5b1d5d2..09f135d 100644
--- a/network/tcp_transport.go
+++ b/network/tcp_transport.go
@@ -2,6 +2,7 @@ package network
 
 import (
 	"bytes"
+	"encoding/binary"
 	"fmt"
 	"io"
 	"net"
@@ -13,14 +14,26 @@ type TCPPeer struct {
 }
 
 func (p *TCPPeer) Send(b []byte) error {
-	_, err := p.conn.Write(b)
+	length := uint32(len(b))
+	lengthBytes := make([]byte, 4)
+	binary.BigEndian.PutUint32(lengthBytes, length)
+	_, err := p.conn.Write(append(lengthBytes, b...))
 	return err
 }
 
 func (p *TCPPeer) readLoop(rpcCh chan RPC) {
-	buf := make([]byte, 4096)
 	for {
-		n, err := p.conn.Read(buf)
+		lengthBuf := make([]byte, 4)
+		if _, err := io.ReadFull(p.conn, lengthBuf); err != nil {
+			if err == io.EOF {
+				continue
+			}
+			panic(err)
+		}
+
+		length := binary.BigEndian.Uint32(lengthBuf)
+		msgBuf := make([]byte, length)
+		_, err := io.ReadFull(p.conn, msgBuf)
 		if err == io.EOF {
 			continue
 		}
@@ -29,10 +42,9 @@ func (p *TCPPeer) readLoop(rpcCh chan RPC) {
 			continue
 		}
 
-		msg := buf[:n]
 		rpcCh <- RPC{
 			From:    p.conn.RemoteAddr(),
-			Payload: bytes.NewReader(msg),
+			Payload: bytes.NewReader(msgBuf),
 		}
 	}
 }