continuity/Server/AuthSession.cs

using System.Security.Cryptography;
using System.Text;
using MassTransit.Mediator;
using Microsoft.Extensions.Logging;
using NetCoreServer;

namespace Server;

public abstract class AuthSession : TcpSession
{
    private readonly ILogger<AuthSession> _logger;
    private readonly IMediator _mediator;

    protected AuthSession(TcpServer
        server, ILogger<AuthSession> logger, IMediator mediator) : base(server)
    {
        _logger = logger;
        _mediator = mediator;
    }

    protected override void OnReceived(byte[] buffer, long offset, long size)
    {
        Console.WriteLine($"Length: {size} & offset: {offset}");
        //Console.WriteLine(BitConverter.ToString(buffer.ToArray()).Replace("-", string.Empty));
        Span<byte> decryptedBuffer = new byte[size];


        // xor every value after the first 8 bytes
        // then apply AES decryption
        var dataBuffer = Decrypt(new ArraySegment<byte>(buffer, 8, (int)size - 8).ToArray());
        /*using (var ms = new MemoryStream(dataBuffer))
        using (var cs = new CryptoStream(ms, _decryptor, CryptoStreamMode.Read))
        {
            cs.Read(decryptedBuffer);
        }*/


        Console.WriteLine("Length " + BitConverter.ToUInt16(buffer, 0));
        var opCode = BitConverter.ToUInt16(buffer.ToArray(), 2);
        Console.WriteLine("Packet Op Code: " + opCode);
        Console.WriteLine("Some Value: " + buffer[4]);
        /*
         *  20s = 5
         *  15s = 4
         *  10s = 3
         *
         *  client alive time * 5s => uptime
         */
        var clientAliveTime = BitConverter.ToUInt16(buffer.ToArray(), 5);
        Console.WriteLine("Client Alive time: " + clientAliveTime);
        Console.WriteLine("Might be a flag:" + buffer[7]);

        Console.WriteLine("username: " + Encoding.ASCII.GetString(dataBuffer.ToArray(), 0, 20));
        Console.WriteLine("password: " + Encoding.ASCII.GetString(dataBuffer.ToArray(), 20, 32));
        Console.WriteLine("Full buffer: " + Encoding.ASCII.GetString(dataBuffer.ToArray()));

        RawPacket rawPacket = new RawPacket((OperationCode)opCode, dataBuffer, clientAliveTime, buffer[0],
            buffer[3],
            Id, this);
        Parallel.Invoke(() => _mediator.Send(rawPacket));
        _logger.LogInformation("Connection from: {@RemoteEndpoint}", Socket.RemoteEndPoint?.ToString());
        base.OnReceived(decryptedBuffer.ToArray(), offset, decryptedBuffer.Length);
    }

    private byte[] Decrypt(byte[] buffer)
    {
        for (int i = 0; i < buffer.Length; ++i)
        {
            buffer[i] = (byte)(buffer[i] ^ i ^ (3 * (0xFE - i)));
        }

        return buffer;
    }
}