Add TcpRpc server and client and split crypto code into multiple classes

Utils/AesGcmCrypto.cs

@@ -0,0 +1,69 @@
+using Org.BouncyCastle.Crypto.Engines;
+using Org.BouncyCastle.Crypto.Modes;
+using Org.BouncyCastle.Crypto.Parameters;
+
+using System.Security.Cryptography;
+using System.Text;
+
+namespace RemSox.Utils;
+
+public static class AesGcmCrypto
+{
+    private const int NonceSize = 12;
+    private const int TagSize = 128;
+
+    public static byte[] Encrypt(byte[] plainData, byte[] key)
+    {
+        byte[] nonce = new byte[NonceSize];
+        RandomNumberGenerator.Fill(nonce);
+
+        GcmBlockCipher cipher = new GcmBlockCipher(new AesEngine());
+        cipher.Init(true, new AeadParameters(new KeyParameter(key), TagSize, nonce));
+
+        byte[] output = new byte[cipher.GetOutputSize(plainData.Length)];
+
+        int len = cipher.ProcessBytes(plainData, 0, plainData.Length, output, 0);
+        _ = cipher.DoFinal(output, len);
+
+        byte[] result = new byte[nonce.Length + output.Length];
+
+        Buffer.BlockCopy(nonce, 0, result, 0, nonce.Length);
+        Buffer.BlockCopy(output, 0, result, nonce.Length, output.Length);
+
+        return result;
+    }
+
+    public static string Encrypt(string text, byte[] key)
+    {
+        byte[] data = Encoding.UTF8.GetBytes(text);
+        return Convert.ToBase64String(Encrypt(data, key));
+    }
+
+    public static byte[] Decrypt(byte[] encryptedData, byte[] key)
+    {
+        byte[] nonce = new byte[NonceSize];
+        Buffer.BlockCopy(encryptedData, 0, nonce, 0, NonceSize);
+
+        int cipherLength = encryptedData.Length - NonceSize;
+        byte[] cipherBytes = new byte[cipherLength];
+
+        Buffer.BlockCopy(encryptedData, NonceSize, cipherBytes, 0, cipherLength);
+
+        GcmBlockCipher cipher = new GcmBlockCipher(new AesEngine());
+        cipher.Init(false, new AeadParameters(new KeyParameter(key), TagSize, nonce));
+
+        byte[] plain = new byte[cipher.GetOutputSize(cipherBytes.Length)];
+
+        int len = cipher.ProcessBytes(cipherBytes, 0, cipherBytes.Length, plain, 0);
+        _ = cipher.DoFinal(plain, len);
+
+        return plain;
+    }
+
+    public static string Decrypt(string cipherText, byte[] key)
+    {
+        byte[] data = Convert.FromBase64String(cipherText);
+        byte[] plain = Decrypt(data, key);
+        return Encoding.UTF8.GetString(plain);
+    }
+}

Utils/PasswordKeyDeriver.cs

@@ -0,0 +1,26 @@
+using Org.BouncyCastle.Crypto;
+using Org.BouncyCastle.Crypto.Digests;
+using Org.BouncyCastle.Crypto.Generators;
+using Org.BouncyCastle.Crypto.Parameters;
+
+namespace RemSox.Utils;
+
+public static class PasswordKeyDeriver
+{
+    private const int KeySize = 32; // 256-bit key
+    private const int Iterations = 150_000; // PBKDF2 cost factor
+
+    public static byte[] DeriveKey(string password, byte[] salt)
+    {
+        Pkcs5S2ParametersGenerator generator = new Pkcs5S2ParametersGenerator(new Sha256Digest());
+
+        generator.Init(
+            PbeParametersGenerator.Pkcs5PasswordToBytes(password.ToCharArray()),
+            salt,
+            Iterations
+        );
+
+        return ((KeyParameter)generator.GenerateDerivedMacParameters(KeySize * 8))
+            .GetKey();
+    }
+}