fix chacha20-ietf with some limitation. refactor Span.Slice usage

shadowsocks-csharp/Controller/LoggerExtension.cs

@@ -17,7 +17,7 @@ namespace NLog
             if (length == -1) length = arr.Length;
 
             if (!logger.IsTraceEnabled) return;
-            string hex = BitConverter.ToString(arr.AsSpan().Slice(0, length).ToArray()).Replace("-", "");
+            string hex = BitConverter.ToString(arr.AsSpan(0, length).ToArray()).Replace("-", "");
             string content = $@"
 {tag}:
 {hex}
@@ -31,7 +31,7 @@ namespace NLog
             if (length == -1) length = arr.Length;
 
             if (!logger.IsTraceEnabled) return;
-             string hex =Convert.ToBase64String(arr.AsSpan().Slice(0, length).ToArray());
+             string hex =Convert.ToBase64String(arr.AsSpan(0, length).ToArray());
             string content = $@"
 {tag}:
 {hex}

shadowsocks-csharp/Encryption/AEAD/AEADEncryptor.cs

@@ -328,13 +328,13 @@ namespace Shadowsocks.Encryption.AEAD
         {
             // Generate salt
             //RNG.GetBytes(outbuf, saltLen);
-            RNG.GetSpan(outbuf.AsSpan().Slice(0, saltLen));
+            RNG.GetSpan(outbuf.AsSpan(0, saltLen));
             InitCipher(outbuf, true, true);
             //uint olen = 0;
             lock (_udpTmpBuf)
             {
                 //cipherEncrypt(buf, (uint)length, _udpTmpBuf, ref olen);
-                var plain = buf.AsSpan().Slice(0, length).ToArray(); // mmp
+                var plain = buf.AsSpan(0, length).ToArray(); // mmp
                 var cipher = CipherEncrypt2(plain);
                 //Debug.Assert(olen == length + tagLen);
                 Buffer.BlockCopy(cipher, 0, outbuf, saltLen, length + tagLen);
@@ -351,7 +351,7 @@ namespace Shadowsocks.Encryption.AEAD
             {
                 // copy remaining data to first pos
                 Buffer.BlockCopy(buf, saltLen, buf, 0, length - saltLen);
-                byte[] b = buf.AsSpan().Slice(0, length - saltLen).ToArray();
+                byte[] b = buf.AsSpan(0, length - saltLen).ToArray();
                 byte[] o = CipherDecrypt2(b);
                 //cipherDecrypt(buf, (uint)(length - saltLen), _udpTmpBuf, ref olen);
                 Buffer.BlockCopy(o, 0, outbuf, 0, o.Length);

shadowsocks-csharp/Encryption/Stream/StreamAesBouncyCastleEncryptor.cs

@@ -25,7 +25,7 @@ namespace Shadowsocks.Encryption.Stream
 
         protected override void cipherUpdate(bool isEncrypt, int length, byte[] buf, byte[] outbuf)
         {
-            var i = buf.AsSpan().Slice(0, length);
+            var i = buf.AsSpan(0, length);
             if (isEncrypt) CipherEncrypt(i, outbuf);
             else CipherDecrypt(outbuf, i);
         }

shadowsocks-csharp/Encryption/Stream/StreamChachaNaClEncryptor.cs

@@ -6,29 +6,36 @@ namespace Shadowsocks.Encryption.Stream
 {
     public class StreamChachaNaClEncryptor : StreamEncryptor
     {
-        readonly ChaCha20 c;
+        // yes, they update over all saved data everytime...
+        byte[] chachaBuf = new byte[65536];
+        int ptr = 0;
         public StreamChachaNaClEncryptor(string method, string password) : base(method, password)
         {
-            c = new ChaCha20(key, 0);
         }
 
         protected override int CipherDecrypt(Span<byte> plain, Span<byte> cipher)
         {
-            var p = c.Decrypt(cipher, iv);
-            p.CopyTo(plain);
-            return p.Length;
+            int len = cipher.Length;
+            cipher.CopyTo(chachaBuf.AsSpan(ptr));
+            var p = new ChaCha20(key, 0).Decrypt(chachaBuf, iv);
+            p.AsSpan(ptr, len).CopyTo(plain);
+            ptr += len;
+            return len;
         }
 
         protected override int CipherEncrypt(Span<byte> plain, Span<byte> cipher)
         {
-            var e = c.Encrypt(plain, iv);
-            e.CopyTo(cipher);
-            return e.Length;
+            int len = plain.Length;
+            plain.CopyTo(chachaBuf.AsSpan(ptr));
+            var p = new ChaCha20(key, 0).Encrypt(chachaBuf, iv);
+            p.AsSpan(ptr, len).CopyTo(cipher);
+            ptr += len;
+            return len;
         }
 
         protected override void cipherUpdate(bool isEncrypt, int length, byte[] buf, byte[] outbuf)
         {
-            var i = buf.AsSpan().Slice(0, length);
+            var i = buf.AsSpan(0, length);
             if (isEncrypt)
             {
                 CipherEncrypt(i, outbuf);

test/CryptographyTest.cs

@@ -67,7 +67,7 @@ namespace Shadowsocks.Test
             encryptor.Encrypt(plain, length, cipher, out int outLen);
             decryptor.Decrypt(cipher, outLen, plain2, out int outLen2);
             Assert.AreEqual(length, outLen2);
-            ArrayEqual<byte>(plain.AsSpan().Slice(0, length).ToArray(), plain2.AsSpan().Slice(0, length).ToArray());
+            ArrayEqual<byte>(plain.AsSpan(0, length).ToArray(), plain2.AsSpan(0, length).ToArray());
         }
 
         private void RunEncryptionRound(IEncryptor encryptor, IEncryptor decryptor)