diff --git a/shadowsocks/crypto/openssl.py b/shadowsocks/crypto/openssl.py
index f2948ae..6abeaa6 100644
--- a/shadowsocks/crypto/openssl.py
+++ b/shadowsocks/crypto/openssl.py
@@ -107,8 +107,11 @@ class OpenSSLCryptoBase(object):
         if not self._ctx:
             raise Exception('can not create cipher context')
 
-        self.encrypt_once = self.update
-        self.decrypt_once = self.update
+    def encrypt_once(self, data):
+        return self.update(data)
+
+    def decrypt_once(self, data):
+        return self.update(data)
 
     def update(self, data):
         """
@@ -281,8 +284,12 @@ class OpenSSLStreamCrypto(OpenSSLCryptoBase):
         if not r:
             self.clean()
             raise Exception('can not initialize cipher context')
-        self.encrypt = self.update
-        self.decrypt = self.update
+
+    def encrypt(self, data):
+        return self.update(data)
+
+    def decrypt(self, data):
+        return self.update(data)
 
 
 ciphers = {
diff --git a/shadowsocks/crypto/sodium.py b/shadowsocks/crypto/sodium.py
index fce65c0..35927e8 100644
--- a/shadowsocks/crypto/sodium.py
+++ b/shadowsocks/crypto/sodium.py
@@ -192,10 +192,18 @@ class SodiumCrypto(object):
             raise Exception('Unknown cipher')
         # byte counter, not block counter
         self.counter = 0
-        self.encrypt = self.update
-        self.decrypt = self.update
-        self.encrypt_once = self.update
-        self.decrypt_once = self.update
+
+    def encrypt(self, data):
+        return self.update(data)
+
+    def decrypt(self, data):
+        return self.update(data)
+
+    def encrypt_once(self, data):
+        return self.update(data)
+
+    def decrypt_once(self, data):
+        return self.update(data)
 
     def update(self, data):
         global buf_size, buf