TLSharp/TLSharp.Core/Auth/Step2_DHExchange.cs

using System;
using System.Collections.Generic;
using System.IO;
using TLSharp.Core.MTProto;
using TLSharp.Core.MTProto.Crypto;

namespace TLSharp.Core.Auth
{
	public class Step2_Response
	{
		public byte[] Nonce { get; set; }
		public byte[] ServerNonce { get; set; }
		public byte[] NewNonce { get; set; }
		public byte[] EncryptedAnswer { get; set; }
	}

	public class Step2_DHExchange
	{
		public byte[] newNonce;

		public Step2_DHExchange()
		{
			newNonce = new byte[32];
		}

		public byte[] ToBytes(byte[] nonce, byte[] serverNonce, List<byte[]> fingerprints, BigInteger pq)
		{
			new Random().NextBytes(newNonce);
			
			var pqPair = Factorizator.Factorize(pq);

			byte[] reqDhParamsBytes;

			using (MemoryStream pqInnerData = new MemoryStream(255))
			{
				using (BinaryWriter pqInnerDataWriter = new BinaryWriter(pqInnerData))
				{
					pqInnerDataWriter.Write(0x83c95aec); // pq_inner_data
					Serializers.Bytes.write(pqInnerDataWriter, pq.ToByteArrayUnsigned());
					Serializers.Bytes.write(pqInnerDataWriter, pqPair.Min.ToByteArrayUnsigned());
					Serializers.Bytes.write(pqInnerDataWriter, pqPair.Max.ToByteArrayUnsigned());
					pqInnerDataWriter.Write(nonce);
					pqInnerDataWriter.Write(serverNonce);
					pqInnerDataWriter.Write(newNonce);

					byte[] ciphertext = null;
					byte[] targetFingerprint = null;
					foreach (byte[] fingerprint in fingerprints)
					{
						ciphertext = RSA.Encrypt(BitConverter.ToString(fingerprint).Replace("-", string.Empty),
												 pqInnerData.GetBuffer(), 0, (int)pqInnerData.Position);
						if (ciphertext != null)
						{
							targetFingerprint = fingerprint;
							break;
						}
					}

					if (ciphertext == null)
					{
						throw new InvalidOperationException(
							String.Format("not found valid key for fingerprints: {0}", String.Join(", ", fingerprints)));
					}

					using (MemoryStream reqDHParams = new MemoryStream(1024))
					{
						using (BinaryWriter reqDHParamsWriter = new BinaryWriter(reqDHParams))
						{
							reqDHParamsWriter.Write(0xd712e4be); // req_dh_params
							reqDHParamsWriter.Write(nonce);
							reqDHParamsWriter.Write(serverNonce);
							Serializers.Bytes.write(reqDHParamsWriter, pqPair.Min.ToByteArrayUnsigned());
							Serializers.Bytes.write(reqDHParamsWriter, pqPair.Max.ToByteArrayUnsigned());
							reqDHParamsWriter.Write(targetFingerprint);
							Serializers.Bytes.write(reqDHParamsWriter, ciphertext);

							reqDhParamsBytes = reqDHParams.ToArray();
						}
					}
				}
				return reqDhParamsBytes;
			}
		}

		public Step2_Response FromBytes(byte[] response)
		{
			byte[] encryptedAnswer;

			using (MemoryStream responseStream = new MemoryStream(response, false))
			{
				using (BinaryReader responseReader = new BinaryReader(responseStream))
				{
					uint responseCode = responseReader.ReadUInt32();

					if (responseCode == 0x79cb045d)
					{
						// server_DH_params_fail
						throw new InvalidOperationException("server_DH_params_fail: TODO");
					}

					if (responseCode != 0xd0e8075c)
					{
						throw new InvalidOperationException($"invalid response code: {responseCode}");						
					}

					byte[] nonceFromServer = responseReader.ReadBytes(16);

					// TODO:!
					/*
					if (!nonceFromServer.SequenceEqual(nonce))
					{
						logger.debug("invalid nonce from server");
						return null;
					}
					*/


					byte[] serverNonceFromServer = responseReader.ReadBytes(16);

					// TODO: !
					/*
					if (!serverNonceFromServer.SequenceEqual(serverNonce))
					{
						logger.error("invalid server nonce from server");
						return null;
					}
					*/

					encryptedAnswer = Serializers.Bytes.read(responseReader);

					return new Step2_Response()
					{
						EncryptedAnswer = encryptedAnswer,
						ServerNonce = serverNonceFromServer,
						Nonce = nonceFromServer,
						NewNonce = newNonce
					};
				}
			}			
		}
	}
}