implement secure rcon for IW4x

Integrations/Cod/SecureRcon/Helpers.cs

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+using System;
+using System.IO;
+using System.Linq;
+using System.Security.Cryptography;
+using ProtoBuf;
+
+namespace Integrations.Cod.SecureRcon;
+
+public static class Helpers
+{
+    private static byte[] ToSerializedMessage(this SecureCommand command)
+    {
+        using var ms = new MemoryStream();
+        Serializer.Serialize(ms, command);
+        return ms.ToArray();
+    }
+    
+    private static byte[] SignData(byte[] data, string privateKey)
+    {
+        using var rsa = new RSACryptoServiceProvider(512);
+        rsa.ImportFromPem(privateKey);
+        var rsaFormatter = new RSAPKCS1SignatureFormatter(rsa);
+        rsaFormatter.SetHashAlgorithm("SHA512");
+        var hash = SHA512.Create();
+        var hashedData = hash.ComputeHash(data);
+        var signature = rsaFormatter.CreateSignature(hashedData);
+
+        return signature;
+    }
+    
+    public static byte SafeConversion(char c)
+    {
+        try
+        {
+            return Convert.ToByte(c);
+        }
+
+        catch
+        {
+            return (byte)'.';
+        }
+    }
+
+    public static byte[] BuildSafeRconPayload(string prefix, string command, string signingKey)
+    {
+        var message = command.Select(SafeConversion).ToArray();
+        var header = (prefix + "\n").Select(SafeConversion).ToArray();
+
+        var secureCommand = new SecureCommand
+        {
+            SecMessage = message,
+            Signature = SignData(message, signingKey)
+        };
+
+        return header.Concat(secureCommand.ToSerializedMessage()).ToArray();
+    }
+}

Integrations/Cod/SecureRcon/SecureCommand.cs

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+using ProtoBuf;
+
+namespace Integrations.Cod.SecureRcon;
+
+[ProtoContract]
+public class SecureCommand
+{
+    [ProtoMember(1)] 
+    public byte[] SecMessage { get; set; }
+    
+    [ProtoMember(2)]
+    public byte[] Signature { get; set; }
+}