add chacha20-ietf support with updated libsscrypto

ChaCha20 with an extended (96 bit) nonce and a 32-bit counter has
been implemented as crypto_stream_chacha20_ietf() from LibSodium 1.0.4

Please refer to https://tools.ietf.org/html/rfc7539 for details.

Signed-off-by: Syrone Wong <wong.syrone@gmail.com>

shadowsocks-csharp/Encryption/Sodium.cs

@@ -40,6 +40,9 @@ namespace Shadowsocks.Encryption
         [DllImport(DLLNAME, CallingConvention = CallingConvention.Cdecl)]
         public extern static int crypto_stream_chacha20_xor_ic(byte[] c, byte[] m, ulong mlen, byte[] n, ulong ic, byte[] k);
 
+        [DllImport(DLLNAME, CallingConvention = CallingConvention.Cdecl)]
+        public extern static int crypto_stream_chacha20_ietf_xor_ic(byte[] c, byte[] m, ulong mlen, byte[] n, uint ic, byte[] k);
+
         [DllImport(DLLNAME, CallingConvention = CallingConvention.Cdecl)]
         public extern static void ss_sha1_hmac_ex(byte[] key, uint keylen,
             byte[] input, int ioff, uint ilen,

shadowsocks-csharp/Encryption/SodiumEncryptor.cs

@@ -10,6 +10,7 @@ namespace Shadowsocks.Encryption
     {
         const int CIPHER_SALSA20 = 1;
         const int CIPHER_CHACHA20 = 2;
+        const int CIPHER_CHACHA20_IETF = 3;
 
         const int SODIUM_BLOCK_SIZE = 64;
 
@@ -29,6 +30,7 @@ namespace Shadowsocks.Encryption
         private static Dictionary<string, int[]> _ciphers = new Dictionary<string, int[]> {
                 {"salsa20", new int[]{32, 8, CIPHER_SALSA20, PolarSSL.AES_CTX_SIZE}},
                 {"chacha20", new int[]{32, 8, CIPHER_CHACHA20, PolarSSL.AES_CTX_SIZE}},
+                {"chacha20-ietf", new int[]{32, 12, CIPHER_CHACHA20_IETF, PolarSSL.AES_CTX_SIZE}},
         };
 
         protected override Dictionary<string, int[]> getCiphers()
@@ -75,6 +77,9 @@ namespace Shadowsocks.Encryption
                     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;

shadowsocks-csharp/View/ConfigForm.Designer.cs

@@ -201,6 +201,7 @@
             "rc4-md5",
             "salsa20",
             "chacha20",
+            "chacha20-ietf",
             "aes-256-cfb",
             "aes-192-cfb",
             "aes-128-cfb"});