67 lines
2.1 KiB
C#
67 lines
2.1 KiB
C#
using System;
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using System.Buffers.Binary;
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using System.Collections.Generic;
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using System.Text;
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namespace AssetStudio
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{
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public static class BlkUtils
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{
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private const int DataOffset = 0x2A;
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private const int KeySize = 0x1000;
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private const int SeedBlockSize = 0x800;
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public static XORStream Decrypt(FileReader reader, Blk blk)
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{
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reader.Endian = EndianType.LittleEndian;
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var signature = reader.ReadStringToNull();
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Logger.Verbose($"Signature: {signature}");
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var count = reader.ReadInt32();
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Logger.Verbose($"Key size: {count}");
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var key = reader.ReadBytes(count);
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reader.Position += count;
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var seedSize = Math.Min(reader.ReadInt16(), blk.SBox.IsNullOrEmpty() ? SeedBlockSize : SeedBlockSize * 2);
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Logger.Verbose($"Seed size: 0x{seedSize:X8}");
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if (!blk.SBox.IsNullOrEmpty() && blk.Type.IsGI())
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{
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for (int i = 0; i < 0x10; i++)
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{
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key[i] = blk.SBox[(i % 4 * 0x100) | key[i]];
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}
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}
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AES.Decrypt(key, blk.ExpansionKey);
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for (int i = 0; i < 0x10; i++)
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{
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key[i] ^= blk.InitVector[i];
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}
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ulong keySeed = ulong.MaxValue;
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var dataPos = reader.Position;
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for (int i = 0; i < seedSize; i += 8)
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{
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keySeed ^= reader.ReadUInt64();
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}
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reader.Position = dataPos;
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var keyLow = BinaryPrimitives.ReadUInt64LittleEndian(key.AsSpan(0, 8));
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var keyHigh = BinaryPrimitives.ReadUInt64LittleEndian(key.AsSpan(8, 8));
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var seed = keyLow ^ keyHigh ^ keySeed ^ blk.InitSeed;
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Logger.Verbose($"Seed: 0x{seed:X8}");
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var mt64 = new MT19937_64(seed);
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var xorpad = new byte[KeySize];
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for (int i = 0; i < KeySize; i += 8)
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{
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BinaryPrimitives.WriteUInt64LittleEndian(xorpad.AsSpan(i, 8), mt64.Int64());
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}
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return new XORStream(reader.BaseStream, DataOffset, xorpad);
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}
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}
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} |