Method DecryptFile

Catalog/NikkeCatalog/Program.cs:44–102

(string inputPath, string outputPath)

	}

	static bool DecryptFile(string inputPath, string outputPath)
	{
		using var fs = new FileStream(inputPath, FileMode.Open, FileAccess.Read);
		using var reader = new BinaryReader(fs);

		var header = new NikkeDatabaseHeader
		{
			Magic = reader.ReadBytes(4),
			Version = ReadUInt32BigEndian(reader),
			AesKey = reader.ReadBytes(16),
			SegmentSize = ReadUInt32BigEndian(reader),
			SegmentCount = ReadUInt32BigEndian(reader)
		};

		if (!header.Magic.SequenceEqual(Encoding.ASCII.GetBytes("NKDB")))
			return false; // invalid magic

		if (header.Version != 1)
			return false; // invalid version

		int lengthByteCount = (header.SegmentSize * header.SegmentCount > 0xFFFFFFFF) ? 5 : 4;

		long ReadOffset()
		{
			byte[] offsetBytes = reader.ReadBytes(lengthByteCount);
			return offsetBytes.Aggregate(0L, (acc, b) => (acc << 8) | b);
		}

		long currentOffset = ReadOffset();
		var segments = new (long Offset, long Length, int Index)[header.SegmentCount];

		for (int i = 0; i < header.SegmentCount; i++)
		{
			long nextOffset = ReadOffset();
			segments[i] = (currentOffset, nextOffset - currentOffset, i);
			currentOffset = nextOffset;
		}

		using var output = new FileStream(outputPath, FileMode.Create, FileAccess.Write);

		foreach (var (offset, length, index) in segments)
		{
			fs.Seek(offset, SeekOrigin.Begin);
			byte[] segment = reader.ReadBytes((int)length);

			byte[] iv = new byte[16];
			BitConverter.GetBytes(index).CopyTo(iv, 0);
			BitConverter.GetBytes((int)offset).CopyTo(iv, 4);

			byte[] decrypted = DecryptAES_OFB(header.AesKey, iv, segment);

			using var ms = new MemoryStream(decrypted);
			using var zlib = new ZLibStream(ms, CompressionMode.Decompress);
			zlib.CopyTo(output);

		}

		return true;