diff --git a/proxy/vmess/protocol/user/id.go b/proxy/vmess/protocol/user/id.go
index ec3af7e95..63348656f 100644
--- a/proxy/vmess/protocol/user/id.go
+++ b/proxy/vmess/protocol/user/id.go
@@ -14,8 +14,8 @@ const (
 // The ID of en entity, in the form of an UUID.
 type ID struct {
 	String string
-	Bytes  []byte
-	cmdKey []byte
+	Bytes  [16]byte
+	cmdKey [16]byte
 }
 
 func NewID(id string) (ID, error) {
@@ -25,27 +25,25 @@ func NewID(id string) (ID, error) {
 	}
 
 	md5hash := md5.New()
-	md5hash.Write(idBytes)
+	md5hash.Write(idBytes[:])
 	md5hash.Write([]byte("c48619fe-8f02-49e0-b9e9-edf763e17e21"))
 	cmdKey := md5.Sum(nil)
 
 	return ID{
 		String: id,
 		Bytes:  idBytes,
-		cmdKey: cmdKey[:],
+		cmdKey: cmdKey,
 	}, nil
 }
 
 func (v ID) CmdKey() []byte {
-	return v.cmdKey
+	return v.cmdKey[:]
 }
 
 var byteGroups = []int{8, 4, 4, 4, 12}
 
 // TODO: leverage a full functional UUID library
-func UUIDToID(uuid string) (v []byte, err error) {
-	v = make([]byte, 16)
-
+func UUIDToID(uuid string) (v [16]byte, err error) {
 	text := []byte(uuid)
 	if len(text) < 32 {
 		err = log.Error("uuid: invalid UUID string: %s", text)
diff --git a/proxy/vmess/protocol/user/id_test.go b/proxy/vmess/protocol/user/id_test.go
index 0e35d96b9..b5d57800d 100644
--- a/proxy/vmess/protocol/user/id_test.go
+++ b/proxy/vmess/protocol/user/id_test.go
@@ -13,5 +13,5 @@ func TestUUIDToID(t *testing.T) {
 	expectedBytes := []byte{0x24, 0x18, 0xd0, 0x87, 0x64, 0x8d, 0x49, 0x90, 0x86, 0xe8, 0x19, 0xdc, 0xa1, 0xd0, 0x06, 0xd3}
 
 	actualBytes, _ := NewID(uuid)
-	assert.Bytes(actualBytes.Bytes).Named("UUID").Equals(expectedBytes)
+	assert.Bytes(actualBytes.Bytes[:]).Named("UUID").Equals(expectedBytes)
 }
diff --git a/proxy/vmess/protocol/user/userset.go b/proxy/vmess/protocol/user/userset.go
index 0575382cc..2e2d2c9be 100644
--- a/proxy/vmess/protocol/user/userset.go
+++ b/proxy/vmess/protocol/user/userset.go
@@ -39,7 +39,7 @@ func NewTimedUserSet() UserSet {
 func (us *TimedUserSet) generateNewHashes(lastSec, nowSec int64, idx int, id ID) {
 	idHash := NewTimeHash(HMACHash{})
 	for lastSec < nowSec+cacheDurationSec {
-		idHash := idHash.Hash(id.Bytes, lastSec)
+		idHash := idHash.Hash(id.Bytes[:], lastSec)
 		log.Debug("Valid User Hash: %v", idHash)
 		us.userHash.Set(string(idHash), indexTimePair{idx, lastSec}, lastSec+2*cacheDurationSec)
 		lastSec++
diff --git a/proxy/vmess/protocol/vmess.go b/proxy/vmess/protocol/vmess.go
index 3d981d740..eec4d8975 100644
--- a/proxy/vmess/protocol/vmess.go
+++ b/proxy/vmess/protocol/vmess.go
@@ -172,7 +172,7 @@ func (request *VMessRequest) ToBytes(idHash user.CounterHash, randomRangeInt64 u
 	}
 
 	counter := randomRangeInt64(time.Now().UTC().Unix(), 30)
-	hash := idHash.Hash(request.UserId.Bytes, counter)
+	hash := idHash.Hash(request.UserId.Bytes[:], counter)
 
 	log.Debug("Writing userhash: %v", hash)
 	buffer = append(buffer, hash...)