[2022DASCTF Apr X FATE 防疫挑战赛]fake QR, real QR

此题考察的是qr码的纠错冗余，利用纠错冗余，将隐写的数据混入到正常数据中，解这个题时用到了boofcv这个java库。原理参考https://jcs.iie.ac.cn/ch/reader/view_abstract.aspx?file_no=20230201&flag=1

/*
 * Copyright (c) 2025, Peter Abeles. All Rights Reserved.
 *
 * This file is part of BoofCV (http://boofcv.org).
 *
 * Licensed under the Apache License, Version 2.0 (the "License");
 * you may not use this file except in compliance with the License.
 * You may obtain a copy of the License at
 *
 *   http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */

package boofcv.examples.fiducial;

import boofcv.abst.fiducial.MicroQrCodeDetector;
import boofcv.alg.fiducial.microqr.MicroQrCode;
import boofcv.alg.fiducial.microqr.MicroQrCodeDecoderBits;
import boofcv.alg.fiducial.microqr.MicroQrCodeEncoder;
import boofcv.alg.fiducial.microqr.MicroQrCodeGenerator;
import boofcv.alg.fiducial.microqr.MicroQrCode.ErrorLevel;
import boofcv.alg.fiducial.qrcode.EciEncoding;
import boofcv.alg.fiducial.qrcode.PackedBits8;
import boofcv.alg.fiducial.qrcode.QrCode;
import boofcv.alg.fiducial.qrcode.QrCodeEncoder;
import boofcv.alg.fiducial.qrcode.QrCode.Mode;
import boofcv.factory.fiducial.ConfigMicroQrCode;
import boofcv.factory.fiducial.FactoryFiducial;
import boofcv.gui.feature.VisualizeShapes;
import boofcv.gui.image.ShowImages;
import boofcv.io.UtilIO;
import boofcv.io.image.ConvertBufferedImage;
import boofcv.io.image.UtilImageIO;
import boofcv.struct.image.GrayU8;
import georegression.struct.point.Point2D_I32;

import static boofcv.alg.fiducial.qrcode.QrCode.Failure.STRING_ENCODING_UNAVAILABLE;

import java.awt.*;
import java.awt.image.BufferedImage;
import java.io.UnsupportedEncodingException;
import java.util.List;

import org.apache.commons.codec.binary.Hex;
import org.ddogleg.struct.DogArray_I8;

/**
 * Shows you how to detect a Micro QR Code inside an image and process the extracted data. Much of the information that
 * is computed while detecting and decoding a QR Code is saved inside the {@link MicroQrCode} class. This can be useful
 * for application developers.
 *
 * @author Peter Abeles
 */
public class ExampleDetectMicroQrCode {
	public static void main( String[] args ) {
		BufferedImage input = UtilImageIO.loadImageNotNull(UtilIO.pathExample("/home/ctf/workspace/MISC_attack/QR/flag_1.png"));
		GrayU8 gray = ConvertBufferedImage.convertFrom(input, (GrayU8)null);

		var config = new ConfigMicroQrCode();
//		config.considerTransposed = false; // by default, it will consider incorrectly encoded markers. Faster if false
		MicroQrCodeDetector<GrayU8> detector = FactoryFiducial.microqr(config, GrayU8.class);

		detector.process(gray);

		// Gets a list of all the qr codes it could successfully detect and decode
		List<MicroQrCode> detections = detector.getDetections();

		Graphics2D g2 = input.createGraphics();
		int strokeWidth = Math.max(4, input.getWidth()/200); // in large images the line can be too thin
		g2.setColor(Color.GREEN);
		g2.setStroke(new BasicStroke(strokeWidth));
		int i=0;
		String m="";
		String n="";
		String o="";
		String flipn="";
		String flipo="";
		for (MicroQrCode qr : detections) {
			//System.out.println("corrected: '" + Hex.encodeHexString(qr.corrected) + "'");
			//System.out.println("rawbits  : '" + Hex.encodeHexString(qr.rawbits).substring(0, 28) + "'");
			//System.out.println("totalBitErrors: '" + qr.totalBitErrors + "'");
			// The message encoded in the marker
			m+=qr.message;
			//System.out.println("message: '" + qr.message + "'");
		
			DogArray_I8 flipr=new DogArray_I8();
			flipr.data=qr.rawbits;
			flipr.size=qr.rawbits.length;
			flipBits8(flipr);
			flipo+=Hex.encodeHexString(flipr.data).substring(24, 28);
			

			
		}

		System.out.println("flipo: '" + flipo+ "'");
		
	}
	
	public static void flipBits8( DogArray_I8 array ) {
		flipBits8(array.data, array.size);
	}
	public static void flipBits8( byte[] array, int size ) {
		for (int j = 0; j < size; j++) {
			array[j] = flipBits8(array[j] & 0xFF);
		}
	}
	public static byte flipBits8( int x ) {
		int b = 0;
		for (int i = 0; i < 8; i++) {
			b <<= 1;
			b |= (x & 1);
			x >>= 1;
		}
		return (byte)b;
	}

}

输出

flipo: '789c73710c760e71ab4ece482c4a4c2e492d8a4fce2fcd2b89cfcc4bc94c4e2cc92f8acf2c8e4f8ccfc94cad050056e11093'

得到的结果其实是zllib压缩的

Cyberchef解压一下