mirror of
https://github.com/GMMan/game-and-watch-decrypt.git
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119 lines
4.5 KiB
C#
119 lines
4.5 KiB
C#
// SPDX-License-Identifier: GPL-3.0-or-later
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/*
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* Game & Watch Encryption Utility
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* Copyright (C) 2020 Yukai Li
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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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* This program is distributed in the hope that it will be useful,
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* but WITHOUT ANY WARRANTY; without even the implied warranty of
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* MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
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* GNU General Public License for more details.
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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 <https://www.gnu.org/licenses/>.
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*/
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using System;
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using System.Collections.Generic;
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using System.Security.Cryptography;
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using System.Text;
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namespace GameAndWatchDecrypt
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{
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class OtfDecCryptor : IDisposable
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{
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Aes aes;
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ICryptoTransform cryptor;
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byte[] iv;
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readonly uint startAddress;
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readonly uint endAddress;
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private bool disposedValue;
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public OtfDecCryptor(byte[] key, byte[] iv, uint startAddress, uint endAddress)
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{
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if (key == null) throw new ArgumentNullException(nameof(key));
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if (iv == null) throw new ArgumentNullException(nameof(iv));
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aes = Aes.Create();
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aes.Key = key;
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aes.Mode = CipherMode.ECB;
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aes.Padding = PaddingMode.None;
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cryptor = aes.CreateEncryptor();
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this.iv = iv;
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// See OTFDEC_RxSTARTADDR and OTFDEC_RxENDADDR
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// MSB 4 bits not discarded for simplicity
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this.startAddress = startAddress & 0xfffff000;
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this.endAddress = (endAddress & 0xfffff000) | 0xfff;
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}
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public void Crypt(byte[] data, int offset, int length, uint dataBase)
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{
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CheckDisposed();
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if (data == null) throw new ArgumentNullException(nameof(data));
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if (offset < 0 || offset > data.Length)
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throw new ArgumentOutOfRangeException(nameof(offset), "Offset negative or past data length.");
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if (offset % (aes.BlockSize / 8) != 0)
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throw new ArgumentException(nameof(offset), "Offset is not multiple of block size.");
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if (length < 0)
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throw new ArgumentOutOfRangeException(nameof(length), "Length is negative");
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if (length % (aes.BlockSize / 8) != 0)
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throw new ArgumentException("Length is not a multiple of block size.", nameof(length));
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if (offset + length > data.Length)
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throw new ArgumentException("Offset and length past end of data.");
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if (dataBase % (aes.BlockSize / 8) != 0)
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throw new ArgumentException("Base address is not block aligned.", nameof(dataBase));
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uint currEndAddr = (uint)(dataBase + offset + length);
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for (uint i = (uint)(dataBase + offset); i < currEndAddr; i += (uint)(aes.BlockSize / 8))
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{
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uint ctr = i >> 4;
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iv[12] = (byte)((iv[12] & 0xf0) | (ctr >> 24));
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iv[13] = (byte)(ctr >> 16);
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iv[14] = (byte)(ctr >> 8);
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iv[15] = (byte)ctr;
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byte[] keyStream = cryptor.TransformFinalBlock(iv, 0, iv.Length);
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if (i >= startAddress && i <= endAddress)
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{
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for (int j = 0; j < keyStream.Length; ++j)
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{
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// We'll do block reversing as required here
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data[i - dataBase + j] ^= keyStream[keyStream.Length - 1 - j];
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}
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}
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}
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}
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void CheckDisposed()
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{
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if (disposedValue) throw new ObjectDisposedException(GetType().FullName);
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}
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protected virtual void Dispose(bool disposing)
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{
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if (!disposedValue)
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{
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if (disposing)
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{
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cryptor.Dispose();
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cryptor = null;
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aes.Dispose();
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aes = null;
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iv = null;
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}
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disposedValue = true;
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}
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}
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public void Dispose()
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{
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// Do not change this code. Put cleanup code in 'Dispose(bool disposing)' method
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Dispose(disposing: true);
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GC.SuppressFinalize(this);
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}
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}
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}
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