123 lines
4 KiB
C#
123 lines
4 KiB
C#
/*************************************************************************
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* ModernUO *
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* Copyright 2019-2026 - ModernUO Development Team *
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* Email: hi@modernuo.com *
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* File: LoginEncryption.cs *
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* *
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* This program is free software: you can redistribute it and/or modify *
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* it under the terms of the GNU General Public License as published by *
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* the Free Software Foundation, either version 3 of the License, or *
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* (at your option) any later version. *
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* *
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* You should have received a copy of the GNU General Public License *
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* along with this program. If not, see <http://www.gnu.org/licenses/>. *
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*************************************************************************/
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using System;
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namespace Server.Network;
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/// <summary>
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/// Implements login packet encryption/decryption using XOR with version-derived keys.
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/// Used for the initial account login packet (0x80).
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/// </summary>
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public sealed class LoginEncryption : IClientEncryption
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{
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private uint _table1;
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private uint _table2;
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private readonly uint _key1;
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private readonly uint _key2;
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public LoginEncryption(uint seed, LoginKeys keys)
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{
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_key1 = keys.Key1;
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_key2 = keys.Key2;
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// Initialize state tables from seed
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_table1 = ((~seed ^ 0x00001357) << 16) | ((seed ^ 0xFFFFAAAA) & 0x0000FFFF);
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_table2 = ((seed ^ 0x43210000) >> 16) | ((~seed ^ 0xABCDFFFF) & 0xFFFF0000);
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}
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/// <summary>
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/// Attempts to initialize login encryption and validate the packet.
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/// Returns true if the packet appears to be validly encrypted with this scheme.
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/// </summary>
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public static bool TryDecrypt(
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ClientVersion version,
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uint seed,
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ReadOnlySpan<byte> encryptedPacket,
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out LoginEncryption encryption)
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{
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const int LoginPacketSize = 62;
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encryption = null;
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var keys = LoginKeys.GetKeys(version);
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if (keys is { Key1: 0, Key2: 0 })
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{
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return false;
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}
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if (encryptedPacket.Length < LoginPacketSize)
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{
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return false;
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}
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// Copy and decrypt
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Span<byte> decrypted = stackalloc byte[LoginPacketSize];
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encryptedPacket[..LoginPacketSize].CopyTo(decrypted);
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var enc = new LoginEncryption(seed, keys);
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enc.ClientDecrypt(decrypted);
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// Validate decrypted packet structure:
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// - Byte 0 must be 0x80 (account login packet ID)
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// - Byte 30 must be 0x00 (null terminator for username)
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// - Byte 60 must be 0x00 (null terminator for password)
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if (decrypted[0] != 0x80 || decrypted[30] != 0x00 || decrypted[60] != 0x00)
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{
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return false;
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}
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// Re-initialize encryption state for actual use
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encryption = new LoginEncryption(seed, keys);
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return true;
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}
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/// <summary>
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/// Decrypts incoming data from the client (in-place).
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/// </summary>
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public void ClientDecrypt(Span<byte> buffer)
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{
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for (var i = 0; i < buffer.Length; i++)
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{
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buffer[i] ^= (byte)(_table1 & 0xFF);
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var edx = _table2;
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var esi = _table1 << 31;
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var eax = _table2 >> 1;
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eax |= esi;
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eax ^= _key1 - 1;
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edx <<= 31;
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eax >>= 1;
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var ecx = _table1 >> 1;
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eax |= esi;
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ecx |= edx;
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eax ^= _key1;
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ecx ^= _key2;
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_table1 = ecx;
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_table2 = eax;
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}
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}
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/// <summary>
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/// Server does not encrypt login responses, so this is a no-op.
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/// </summary>
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public void ServerEncrypt(Span<byte> buffer)
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{
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// Login encryption is client-to-server only
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}
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}
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