一、app1

题目链接：https://adworld.xctf.org.cn/task/task_list?type=mobile&number=6&grade=0

二、答题步骤

1.运行app

2.jadx反编译apk文件

搜索再接字符串

找到源码

package com.example.yaphetshan.tencentgreat;

import android.content.pm.PackageInfo;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View;
import android.widget.Button;
import android.widget.EditText;
import android.widget.Toast;

/* loaded from: classes.dex */
public class MainActivity extends AppCompatActivity {
    Button btn;
    public final String pName = BuildConfig.APPLICATION_ID;
    EditText text;

    /* JADX INFO: Access modifiers changed from: protected */
    @Override // android.support.v7.app.AppCompatActivity, android.support.v4.app.FragmentActivity, android.support.v4.app.BaseFragmentActivityGingerbread, android.app.Activity
    public void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_main);
        this.btn = (Button) findViewById(R.id.checBtn);
        this.text = (EditText) findViewById(R.id.input);
        this.btn.setOnClickListener(new View.OnClickListener() { // from class: com.example.yaphetshan.tencentgreat.MainActivity.1
            @Override // android.view.View.OnClickListener
            public void onClick(View v) {
                try {
                    String inputString = MainActivity.this.text.getText().toString();
                    PackageInfo pinfo = MainActivity.this.getPackageManager().getPackageInfo(BuildConfig.APPLICATION_ID, 16384);
                    String versionCode = pinfo.versionName;
                    int versionName = pinfo.versionCode;
                    int i = 0;
                    while (i < inputString.length() && i < versionCode.length()) {
                        if (inputString.charAt(i) != (versionCode.charAt(i) ^ versionName)) {
                            Toast.makeText(MainActivity.this, "再接再厉，加油~", 1).show();
                            return;
                        }
                        i++;
                    }
                    if (inputString.length() == versionCode.length()) {
                        Toast.makeText(MainActivity.this, "恭喜开启闯关之门！", 1).show();
                        return;
                    }
                } catch (PackageManager.NameNotFoundException e) {
                }
                Toast.makeText(MainActivity.this, "年轻人不要耍小聪明噢", 1).show();
            }
        });
    }
}

点击BuildConfig文件，得到这两个参数的值，如下图所示：

package com.example.yaphetshan.tencentgreat;

/* loaded from: classes.dex */
public final class BuildConfig {
    public static final String APPLICATION_ID = "com.example.yaphetshan.tencentgreat";
    public static final String BUILD_TYPE = "debug";
    public static final boolean DEBUG = Boolean.parseBoolean("true");
    public static final String FLAVOR = "";
    public static final int VERSION_CODE = 15;
    public static final String VERSION_NAME = "X<cP[?PHNB<P?aj";
}

看源码得知事进行异或运算上脚本

str = "X<cP[?PHNB<P?aj" #传入版本名
for i in str:   #对版本名进行循环
    sum = ord(i)^15  #sum接收i的每个字符串转ASCII数值并与版本号进行异或的值
    print(chr(sum),end='') #把sum的值转字符串并拼接

得到flag：W3l_T0_GAM3_0ne

总结

反编译技巧 + 读代码 + 异或代码运算