diff --git a/common/alloc/buffer.go b/common/alloc/buffer.go
index eea2866c2..96de75871 100644
--- a/common/alloc/buffer.go
+++ b/common/alloc/buffer.go
@@ -63,13 +63,8 @@ func (b *Buffer) Append(data []byte) *Buffer {
 // Prepend prepends bytes in front of the buffer. Caller must ensure total bytes prepended is
 // no more than 16 bytes.
 func (b *Buffer) Prepend(data []byte) *Buffer {
-	newoffset := b.offset - len(data)
-	if newoffset < 0 {
-		newoffset = 0
-	}
-	copy(b.head[newoffset:], data)
-	b.Value = b.head[newoffset : b.offset+len(b.Value)]
-	b.offset = newoffset
+	b.SliceBack(len(data))
+	copy(b.Value, data)
 	return b
 }
 
@@ -89,6 +84,16 @@ func (b *Buffer) SliceFrom(from int) *Buffer {
 	return b
 }
 
+func (b *Buffer) SliceBack(offset int) *Buffer {
+	newoffset := b.offset - offset
+	if newoffset < 0 {
+		newoffset = 0
+	}
+	b.Value = b.head[newoffset : b.offset+len(b.Value)]
+	b.offset = newoffset
+	return b
+}
+
 // Len returns the length of the buffer content.
 func (b *Buffer) Len() int {
 	return len(b.Value)
diff --git a/proxy/shadowsocks/shadowsocks.go b/proxy/shadowsocks/shadowsocks.go
index d31fed3d2..8878aca6a 100644
--- a/proxy/shadowsocks/shadowsocks.go
+++ b/proxy/shadowsocks/shadowsocks.go
@@ -187,20 +187,18 @@ func (this *Shadowsocks) handleConnection(conn *hub.TCPConn) {
 	var writeFinish sync.Mutex
 	writeFinish.Lock()
 	go func() {
-		firstChunk := alloc.NewBuffer().Slice(0, this.config.Cipher.IVSize())
-		defer firstChunk.Release()
-
-		writer, err := this.config.Cipher.NewEncodingStream(key, firstChunk.Value, conn)
-		if err != nil {
-			log.Error("Shadowsocks: Failed to create encoding stream: ", err)
-			return
-		}
-
 		if payload, ok := <-ray.InboundOutput(); ok {
-			firstChunk.Append(payload.Value)
-			payload.Release()
+			payload.SliceBack(16)
+			rand.Read(payload.Value[:16])
 
-			writer.Write(firstChunk.Value)
+			writer, err := this.config.Cipher.NewEncodingStream(key, payload.Value[:16], conn)
+			if err != nil {
+				log.Error("Shadowsocks: Failed to create encoding stream: ", err)
+				return
+			}
+
+			writer.Write(payload.Value)
+			payload.Release()
 			v2io.ChanToWriter(writer, ray.InboundOutput())
 		}
 		writeFinish.Unlock()