BUUCTF Java逆向解密 RE

Java逆向，百度一下采用Jadx-gui
打开后得到如下代码

package defpackage;

import java.util.ArrayList;
import java.util.Scanner;

/* renamed from: Reverse  reason: default package */
/* loaded from: Reverse.class */
public class Reverse {
    public static void main(String[] args) {
        Scanner s = new Scanner(System.in);
        System.out.println("Please input the flag ：");
        String str = s.next();
        System.out.println("Your input is ：");
        System.out.println(str);
        char[] stringArr = str.toCharArray();
        Encrypt(stringArr);
    }

    public static void Encrypt(char[] arr) {
        ArrayList<Integer> Resultlist = new ArrayList<>();
        for (char c : arr) {
            int result = (c + '@') ^ 32;
            Resultlist.add(Integer.valueOf(result));
        }
        int[] KEY = {180, 136, 137, 147, 191, 137, 147, 191, 148, 136, 133, 191, 134, 140, 129, 135, 191, 65};
        ArrayList<Integer> KEYList = new ArrayList<>();
        for (int i : KEY) {
            KEYList.add(Integer.valueOf(i));
        }
        System.out.println("Result:");
        if (Resultlist.equals(KEYList)) {
            System.out.println("Congratulations！");
        } else {
            System.err.println("Error！");
        }
    }
}

核心代码就是int result = (c + '@') ^ 32;
对所输入字符串字符+64 ^ 32后若和KEY中的值相同即为正确的flag
脚本如下

点击查看

key = [180, 136, 137, 147, 191, 137, 147, 191, 148, 136, 133, 191, 134, 140, 129, 135, 191, 65]
flag =""
for i in range(len(key)):
  flag+=chr((key[i]^32)-64)
print(flag)

得到flagThis_is_the_flag_!