BUUCTF Java逆向解密 1

Class文件是Java编译后的二进制字节码文件。
我这里使用的是jadx-gui，直接将class文件拖进去即可

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！");}}
}

代码的逻辑也非常简单

if (Resultlist.equals(KEYList)) {System.out.println("Congratulations！");
}

主要就是我们输入的值最后需要等于KEYList这个数组，而KEYList的值就是

int[] KEY = {180, 136, 137, 147, 191, 137, 147, 191, 148, 136, 133, 191, 134, 140, 129, 135, 191, 65};

exp

java

public class Test {public static void main(String[] args) {int[] KEY = {180, 136, 137, 147, 191, 137, 147, 191, 148, 136, 133, 191, 134, 140, 129, 135, 191, 65};char cArr[] = new char[KEY.length * 2];for (int i = 0; i < KEY.length; i++) cArr[i] = (char)((KEY[i] ^ 32 ) - '@');System.out.println(new String(cArr));}}

python

KEY = [180, 136, 137, 147, 191, 137, 147, 191,148, 136, 133, 191, 134, 140, 129, 135, 191, 65]
cArr = [chr(((KEY[i] ^ 32) - ord('@'))) for i in range(len(KEY))]
print(''.join(cArr))

flag

flag{This_is_the_flag_!}