diff --git a/shadowsocks-csharp/Encryption/SodiumEncryptor.cs b/shadowsocks-csharp/Encryption/SodiumEncryptor.cs
index 661a90af..7dd42d2e 100755
--- a/shadowsocks-csharp/Encryption/SodiumEncryptor.cs
+++ b/shadowsocks-csharp/Encryption/SodiumEncryptor.cs
@@ -12,16 +12,18 @@ namespace Shadowsocks.Encryption
 
         const int SODIUM_BLOCK_SIZE = 64;
 
-        static byte[] sodiumBuf = new byte[MAX_INPUT_SIZE + SODIUM_BLOCK_SIZE];
-
         protected int _encryptBytesRemaining;
         protected int _decryptBytesRemaining;
         protected ulong _encryptIC;
         protected ulong _decryptIC;
+        protected byte[] _encryptBuf;
+        protected byte[] _decryptBuf;
 
         public SodiumEncryptor(string method, string password, bool onetimeauth, bool isudp)
             : base(method, password, onetimeauth, isudp)
         {
+            _encryptBuf = new byte[MAX_INPUT_SIZE + SODIUM_BLOCK_SIZE];
+            _decryptBuf = new byte[MAX_INPUT_SIZE + SODIUM_BLOCK_SIZE];
         }
 
         private static Dictionary<string, EncryptorInfo> _ciphers = new Dictionary<string, EncryptorInfo> {
@@ -45,54 +47,52 @@ namespace Shadowsocks.Encryption
             // TODO write a unidirection cipher so we don't have to if if if
             int bytesRemaining;
             ulong ic;
+            byte[] sodiumBuf;
             byte[] iv;
 
-            // I'm tired. just add a big lock
-            // let's optimize for RAM instead of CPU
-            lock(sodiumBuf)
+            if (isCipher)
+            {
+                bytesRemaining = _encryptBytesRemaining;
+                ic = _encryptIC;
+                sodiumBuf = _encryptBuf;
+                iv = _encryptIV;
+            }
+            else
             {
-                if (isCipher)
-                {
-                    bytesRemaining = _encryptBytesRemaining;
-                    ic = _encryptIC;
-                    iv = _encryptIV;
-                }
-                else
-                {
-                    bytesRemaining = _decryptBytesRemaining;
-                    ic = _decryptIC;
-                    iv = _decryptIV;
-                }
-                int padding = bytesRemaining;
-                Buffer.BlockCopy(buf, 0, sodiumBuf, padding, length);
+                bytesRemaining = _decryptBytesRemaining;
+                ic = _decryptIC;
+                sodiumBuf = _decryptBuf;
+                iv = _decryptIV;
+            }
+            int padding = bytesRemaining;
+            Buffer.BlockCopy(buf, 0, sodiumBuf, padding, length);
 
-                switch (_cipher)
-                {
-                    case CIPHER_SALSA20:
-                        Sodium.crypto_stream_salsa20_xor_ic(sodiumBuf, sodiumBuf, (ulong)(padding + length), iv, ic, _key);
-                        break;
-                    case CIPHER_CHACHA20:
-                        Sodium.crypto_stream_chacha20_xor_ic(sodiumBuf, sodiumBuf, (ulong)(padding + length), iv, ic, _key);
-                        break;
-                    case CIPHER_CHACHA20_IETF:
-                        Sodium.crypto_stream_chacha20_ietf_xor_ic(sodiumBuf, sodiumBuf, (ulong)(padding + length), iv, (uint)ic, _key);
-                        break;
-                }
-                Buffer.BlockCopy(sodiumBuf, padding, outbuf, 0, length);
-                padding += length;
-                ic += (ulong)padding / SODIUM_BLOCK_SIZE;
-                bytesRemaining = padding % SODIUM_BLOCK_SIZE;
+            switch (_cipher)
+            {
+                case CIPHER_SALSA20:
+                    Sodium.crypto_stream_salsa20_xor_ic(sodiumBuf, sodiumBuf, (ulong)(padding + length), iv, ic, _key);
+                    break;
+                case CIPHER_CHACHA20:
+                    Sodium.crypto_stream_chacha20_xor_ic(sodiumBuf, sodiumBuf, (ulong)(padding + length), iv, ic, _key);
+                    break;
+                case CIPHER_CHACHA20_IETF:
+                    Sodium.crypto_stream_chacha20_ietf_xor_ic(sodiumBuf, sodiumBuf, (ulong)(padding + length), iv, (uint)ic, _key);
+                    break;
+            }
+            Buffer.BlockCopy(sodiumBuf, padding, outbuf, 0, length);
+            padding += length;
+            ic += (ulong)padding / SODIUM_BLOCK_SIZE;
+            bytesRemaining = padding % SODIUM_BLOCK_SIZE;
 
-                if (isCipher)
-                {
-                    _encryptBytesRemaining = bytesRemaining;
-                    _encryptIC = ic;
-                }
-                else
-                {
-                    _decryptBytesRemaining = bytesRemaining;
-                    _decryptIC = ic;
-                }
+            if (isCipher)
+            {
+                _encryptBytesRemaining = bytesRemaining;
+                _encryptIC = ic;
+            }
+            else
+            {
+                _decryptBytesRemaining = bytesRemaining;
+                _decryptIC = ic;
             }
         }