Core: port AES-256-CTR from BoringSSL

Author: aarani

src/TgSharp.Core/MTProto/Crypto/AesCtr.cs

@@ -0,0 +1,96 @@
+using System;
+using System.Collections.Generic;
+using System.Linq;
+using System.Security.Cryptography;
+using System.Text;
+using System.Threading.Tasks;
+
+namespace TgSharp.Core.MTProto.Crypto
+{
+    /*
+     * AES-256-CTR Implementation 
+     * Original implementation by OpenSSL, ported to C#
+     */
+    public class AesCtr
+    {
+        // The input encrypted as though 128bit counter mode is being used.  The extra
+        // state information to record how much of the 128bit block we have used is
+        // contained in number, and the encrypted counter is kept in encryptedCount.  Both
+        // *num and ecount_buf must be initialised with zeros before the first call to
+        // CRYPTO_ctr128_encrypt().
+        //
+        // This algorithm assumes that the counter is in the x lower bits of the IV
+        // (ivec), and that the application has full control over overflow and the rest
+        // of the IV.  This implementation takes NO responsibility for checking that
+        // the counter doesn't overflow into the rest of the IV when incremented.
+
+        public static void Ctr128Encrypt(byte[] input, byte[] key, ref byte[] ivec, ref byte[] encryptedCount, ref int number, byte[] output)
+        {
+            int n;
+            n = number;
+
+            int outputPos = 0, inputPos = 0;
+            int len = input.Length;
+
+            while (n != 0 && len != 0)
+            {
+                output[outputPos++] = (byte)(input[inputPos++] ^ encryptedCount[n]);
+                --len;
+                n = (n + 1) % 16;
+            }
+
+            while (len >= 16)
+            {
+                encryptedCount = EncryptBlock(ivec, key);
+                Ctr128Inc(ivec);
+                for (n = 0; n < 16; n += sizeof(ulong))
+                {
+                    var xoredResult = BitConverter.GetBytes(BitConverter.ToUInt64(input, inputPos + n) ^ BitConverter.ToUInt64(encryptedCount, n));
+                    Buffer.BlockCopy(xoredResult, 0, output, outputPos + n, 8);
+                }
+                len -= 16;
+                outputPos += 16;
+                inputPos += 16;
+                n = 0;
+            }
+
+            if (len != 0)
+            {
+                encryptedCount = EncryptBlock(ivec, key);
+                Ctr128Inc(ivec);
+                while (len-- != 0)
+                {
+                    output[outputPos + n] = (byte)(input[inputPos + n] ^ encryptedCount[n]);
+                    ++n;
+                }
+            }
+            number = n;
+        }
+
+        // increment counter (128-bit int) by 1
+        private static void Ctr128Inc(byte[] counter)
+        {
+            uint n = 16, c = 1;
+
+            do
+            {
+                --n;
+                c += counter[n];
+                counter[n] = (byte)c;
+                c >>= 8;
+            } while (n != 0);
+        }
+
+        private static byte[] EncryptBlock(byte[] toEncrypt, byte[] key)
+        {
+            using (var aes = new RijndaelManaged())
+            {
+                aes.Key = key;
+                aes.Mode = CipherMode.ECB;
+                aes.Padding = PaddingMode.None;
+                ICryptoTransform cTransform = aes.CreateEncryptor();
+                return cTransform.TransformFinalBlock(toEncrypt, 0, toEncrypt.Length);
+            }
+        }
+    }
+}

src/TgSharp.Core/TgSharp.Core.csproj

@@ -53,6 +53,7 @@
     <Compile Include="Exceptions\InvalidPhoneCodeException.cs" />
     <Compile Include="Exceptions\MissingApiConfigurationException.cs" />
     <Compile Include="MTProto\Crypto\AES.cs" />
+    <Compile Include="MTProto\Crypto\AesCtr.cs" />
     <Compile Include="MTProto\Crypto\AuthKey.cs" />
     <Compile Include="MTProto\Crypto\BigInteger.cs" />
     <Compile Include="MTProto\Crypto\Crc32.cs" />