diff --git a/cli/ss-local/main.go b/cli/ss-local/main.go
index a7d9928..680f419 100644
--- a/cli/ss-local/main.go
+++ b/cli/ss-local/main.go
@@ -211,21 +211,16 @@ func newClient(f *flags) (*client, error) {
 			}
 			c.method = method
 		} else if common.Contains(shadowaead_2022.List, f.Method) {
-			var pskList [][shadowaead_2022.KeySaltSize]byte
+			var pskList [][]byte
 			if f.Key != "" {
 				keyStrList := strings.Split(f.Key, ":")
-				pskList = make([][shadowaead_2022.KeySaltSize]byte, len(keyStrList))
+				pskList = make([][]byte, len(keyStrList))
 				for i, keyStr := range keyStrList {
-					var psk [shadowaead_2022.KeySaltSize]byte
 					kb, err := base64.StdEncoding.DecodeString(keyStr)
 					if err != nil {
 						return nil, E.Cause(err, "decode key")
 					}
-					if len(kb) != shadowaead_2022.KeySaltSize {
-						return nil, shadowaead.ErrBadKey
-					}
-					copy(psk[:], kb)
-					pskList[i] = psk
+					pskList[i] = kb
 				}
 			}
 			method, err := shadowaead_2022.New(f.Method, pskList, rng)
diff --git a/cli/ss-server/main.go b/cli/ss-server/main.go
index 4301163..210cc1c 100644
--- a/cli/ss-server/main.go
+++ b/cli/ss-server/main.go
@@ -149,16 +149,13 @@ func newServer(f *flags) (*server, error) {
 		}
 		s.service = service
 	} else if common.Contains(shadowaead_2022.List, f.Method) {
-		var key [shadowaead_2022.KeySaltSize]byte
+		var key []byte
 		if f.Key != "" {
 			kb, err := base64.StdEncoding.DecodeString(f.Key)
 			if err != nil {
 				return nil, E.Cause(err, "decode key")
 			}
-			if len(kb) != shadowaead_2022.KeySaltSize {
-				return nil, shadowaead.ErrBadKey
-			}
-			copy(key[:], kb)
+			key = kb
 		}
 		service, err := shadowaead_2022.NewService(f.Method, key, random.Default, udpTimeout, s)
 		if err != nil {
diff --git a/protocol/shadowsocks/shadowaead_2022/protocol.go b/protocol/shadowsocks/shadowaead_2022/protocol.go
index afc1e0c..842b8a8 100644
--- a/protocol/shadowsocks/shadowaead_2022/protocol.go
+++ b/protocol/shadowsocks/shadowaead_2022/protocol.go
@@ -65,7 +65,6 @@ var List = []string{
 func New(method string, pskList [][]byte, secureRNG io.Reader) (shadowsocks.Method, error) {
 	m := &Method{
 		name:         method,
-		psk:          pskList[len(pskList)-1],
 		pskList:      pskList,
 		secureRNG:    secureRNG,
 		replayFilter: replay.NewCuckoo(60),
@@ -85,12 +84,16 @@ func New(method string, pskList [][]byte, secureRNG io.Reader) (shadowsocks.Meth
 		m.constructor = newChacha20Poly1305
 	}
 
-	for _, psk := range pskList {
-		if len(psk) != m.keyLength {
+	for i, psk := range pskList {
+		if len(psk) < m.keyLength {
 			return nil, shadowaead.ErrBadKey
+		} else if len(psk) > m.keyLength {
+			pskList[i] = DerivePSK(psk, m.keyLength)
 		}
 	}
 
+	m.psk = pskList[len(pskList)-1]
+
 	if len(pskList) > 1 {
 		pskHash := make([]byte, (len(pskList)-1)*aes.BlockSize)
 		for i, psk := range pskList {
@@ -111,10 +114,17 @@ func New(method string, pskList [][]byte, secureRNG io.Reader) (shadowsocks.Meth
 	case "2022-blake3-chacha20-poly1305":
 		m.udpCipher = newXChacha20Poly1305(m.psk)
 	}
+
 	return m, nil
 }
 
-func Blake3DeriveKey(psk []byte, salt []byte, keyLength int) []byte {
+func DerivePSK(key []byte, keyLength int) []byte {
+	outKey := buf.Make(keyLength)
+	blake3.DeriveKey(outKey, "shadowsocks 2022 pre shared key", key)
+	return outKey
+}
+
+func DeriveSessionKey(psk []byte, salt []byte, keyLength int) []byte {
 	sessionKey := buf.Make(len(psk) + len(salt))
 	copy(sessionKey, psk)
 	copy(sessionKey[len(psk):], salt)
@@ -232,7 +242,7 @@ func (c *clientConn) writeRequest(payload []byte) error {
 	salt := make([]byte, SaltSize)
 	common.Must1(io.ReadFull(c.method.secureRNG, salt))
 
-	key := Blake3DeriveKey(c.method.psk, salt, c.method.keyLength)
+	key := DeriveSessionKey(c.method.psk, salt, c.method.keyLength)
 	writer := shadowaead.NewWriter(
 		c.Conn,
 		c.method.constructor(common.Dup(key)),
@@ -301,7 +311,7 @@ func (c *clientConn) readResponse() error {
 		return E.New("salt not unique")
 	}
 
-	key := Blake3DeriveKey(c.method.psk, salt, c.method.keyLength)
+	key := DeriveSessionKey(c.method.psk, salt, c.method.keyLength)
 	runtime.KeepAlive(_salt)
 	reader := shadowaead.NewReader(
 		c.Conn,
@@ -516,7 +526,7 @@ func (c *clientPacketConn) ReadPacket(buffer *buf.Buffer) (M.Socksaddr, error) {
 		} else if sessionId == c.session.lastRemoteSessionId {
 			remoteCipher = c.session.lastRemoteCipher
 		} else {
-			key := Blake3DeriveKey(c.method.psk, packetHeader[:8], c.method.keyLength)
+			key := DeriveSessionKey(c.method.psk, packetHeader[:8], c.method.keyLength)
 			remoteCipher = c.method.constructor(common.Dup(key))
 			runtime.KeepAlive(key)
 		}
@@ -716,7 +726,7 @@ func (m *Method) newUDPSession() *udpSession {
 	if m.udpCipher == nil {
 		sessionId := make([]byte, 8)
 		binary.BigEndian.PutUint64(sessionId, session.sessionId)
-		key := Blake3DeriveKey(m.psk, sessionId, m.keyLength)
+		key := DeriveSessionKey(m.psk, sessionId, m.keyLength)
 		session.cipher = m.constructor(common.Dup(key))
 		runtime.KeepAlive(key)
 	}
diff --git a/protocol/shadowsocks/shadowaead_2022/service.go b/protocol/shadowsocks/shadowaead_2022/service.go
index b7d6055..e1fcf9b 100644
--- a/protocol/shadowsocks/shadowaead_2022/service.go
+++ b/protocol/shadowsocks/shadowaead_2022/service.go
@@ -45,7 +45,6 @@ type Service struct {
 func NewService(method string, psk []byte, secureRNG io.Reader, udpTimeout int64, handler shadowsocks.Handler) (shadowsocks.Service, error) {
 	s := &Service{
 		name:         method,
-		psk:          psk,
 		secureRNG:    secureRNG,
 		replayFilter: replay.NewCuckoo(60),
 		handler:      handler,
@@ -70,17 +69,20 @@ func NewService(method string, psk []byte, secureRNG io.Reader, udpTimeout int64
 		s.constructor = newChacha20Poly1305
 	}
 
-	if len(psk) != s.keyLength {
+	if len(psk) < s.keyLength {
 		return nil, shadowaead.ErrBadKey
+	} else if len(psk) > s.keyLength {
+		psk = DerivePSK(psk, s.keyLength)
 	}
 
+	s.psk = psk
 	switch method {
 	case "2022-blake3-aes-128-gcm":
-		s.udpBlockCipher = newAES(s.psk[:])
+		s.udpBlockCipher = newAES(psk)
 	case "2022-blake3-aes-256-gcm":
-		s.udpBlockCipher = newAES(s.psk[:])
+		s.udpBlockCipher = newAES(psk)
 	case "2022-blake3-chacha20-poly1305":
-		s.udpCipher = newXChacha20Poly1305(s.psk[:])
+		s.udpCipher = newXChacha20Poly1305(psk)
 	}
 
 	return s, nil
@@ -105,7 +107,7 @@ func (s *Service) newConnection(ctx context.Context, conn net.Conn, metadata M.M
 		return E.New("salt not unique")
 	}
 
-	requestKey := Blake3DeriveKey(s.psk[:], requestSalt, s.keyLength)
+	requestKey := DeriveSessionKey(s.psk, requestSalt, s.keyLength)
 	reader := shadowaead.NewReader(
 		conn,
 		s.constructor(common.Dup(requestKey)),
@@ -176,7 +178,7 @@ func (c *serverConn) writeResponse(payload []byte) (n int, err error) {
 	var _salt [SaltSize]byte
 	salt := common.Dup(_salt[:])
 	common.Must1(io.ReadFull(c.secureRNG, salt))
-	key := Blake3DeriveKey(c.uPSK[:], salt, c.keyLength)
+	key := DeriveSessionKey(c.uPSK, salt, c.keyLength)
 	runtime.KeepAlive(_salt)
 	writer := shadowaead.NewWriter(
 		c.Conn,
@@ -292,7 +294,7 @@ func (s *Service) newPacket(conn N.PacketConn, buffer *buf.Buffer, metadata M.Me
 	if !loaded {
 		session.remoteSessionId = sessionId
 		if packetHeader != nil {
-			key := Blake3DeriveKey(s.psk[:], packetHeader[:8], s.keyLength)
+			key := DeriveSessionKey(s.psk, packetHeader[:8], s.keyLength)
 			session.remoteCipher = s.constructor(common.Dup(key))
 			runtime.KeepAlive(key)
 		}
@@ -437,7 +439,7 @@ func (m *Service) newUDPSession() *serverUDPSession {
 	if m.udpCipher == nil {
 		sessionId := make([]byte, 8)
 		binary.BigEndian.PutUint64(sessionId, session.sessionId)
-		key := Blake3DeriveKey(m.psk[:], sessionId, m.keyLength)
+		key := DeriveSessionKey(m.psk, sessionId, m.keyLength)
 		session.cipher = m.constructor(common.Dup(key))
 		runtime.KeepAlive(key)
 	}
diff --git a/protocol/shadowsocks/shadowaead_2022/service_multi.go b/protocol/shadowsocks/shadowaead_2022/service_multi.go
index c55d4d4..9e2880d 100644
--- a/protocol/shadowsocks/shadowaead_2022/service_multi.go
+++ b/protocol/shadowsocks/shadowaead_2022/service_multi.go
@@ -29,9 +29,15 @@ type MultiService[U comparable] struct {
 	uPSKHashR map[[aes.BlockSize]byte]U
 }
 
-func (s *MultiService[U]) AddUser(user U, key []byte) {
+func (s *MultiService[U]) AddUser(user U, key []byte) error {
+	if len(key) < s.keyLength {
+		return shadowaead.ErrBadKey
+	} else if len(key) > s.keyLength {
+		key = DerivePSK(key, s.keyLength)
+	}
+
 	var uPSKHash [aes.BlockSize]byte
-	hash512 := blake3.Sum512(key[:])
+	hash512 := blake3.Sum512(key)
 	copy(uPSKHash[:], hash512[:])
 
 	if oldHash, loaded := s.uPSKHash[user]; loaded {
@@ -40,8 +46,9 @@ func (s *MultiService[U]) AddUser(user U, key []byte) {
 
 	s.uPSKHash[user] = uPSKHash
 	s.uPSKHashR[uPSKHash] = user
-
 	s.uPSK[user] = key
+
+	return nil
 }
 
 func (s *MultiService[U]) RemoveUser(user U) {
@@ -102,7 +109,7 @@ func (s *MultiService[U]) newConnection(ctx context.Context, conn net.Conn, meta
 	}
 
 	keyMaterial := buf.Make(s.keyLength + SaltSize)
-	copy(keyMaterial, s.psk[:])
+	copy(keyMaterial, s.psk)
 	copy(keyMaterial[s.keyLength:], requestSalt)
 	_identitySubkey := buf.Make(s.keyLength)
 	identitySubkey := common.Dup(_identitySubkey)
@@ -119,7 +126,7 @@ func (s *MultiService[U]) newConnection(ctx context.Context, conn net.Conn, meta
 		return E.New("invalid request")
 	}
 
-	requestKey := Blake3DeriveKey(uPSK[:], requestSalt, s.keyLength)
+	requestKey := DeriveSessionKey(uPSK, requestSalt, s.keyLength)
 	reader := shadowaead.NewReader(
 		conn,
 		s.constructor(common.Dup(requestKey)),
@@ -223,7 +230,7 @@ func (s *MultiService[U]) newPacket(conn N.PacketConn, buffer *buf.Buffer, metad
 	})
 	if !loaded {
 		session.remoteSessionId = sessionId
-		key := Blake3DeriveKey(uPSK[:], packetHeader[:8], s.keyLength)
+		key := DeriveSessionKey(uPSK, packetHeader[:8], s.keyLength)
 		session.remoteCipher = s.constructor(common.Dup(key))
 		runtime.KeepAlive(key)
 	}
@@ -305,7 +312,7 @@ func (m *MultiService[U]) newUDPSession(uPSK []byte) *serverUDPSession {
 	session.packetId--
 	sessionId := make([]byte, 8)
 	binary.BigEndian.PutUint64(sessionId, session.sessionId)
-	key := Blake3DeriveKey(uPSK[:], sessionId, m.keyLength)
+	key := DeriveSessionKey(uPSK, sessionId, m.keyLength)
 	session.cipher = m.constructor(common.Dup(key))
 	runtime.KeepAlive(key)
 	return session