【re】BUUCTF Java逆向解密,5r

文件名：【re】BUUCTF Java逆向解密,5r 【re】BUUCTF Java逆向解密

题目：BUUCTF Java逆向解密

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没壳，是java文件（大概） ida打开看不懂，找了网页上的java反编译 Decompiler.com 没用过java啊…暂且用sublime打开 还好还挺好懂的

import java.util.ArrayList;import java.util.Scanner;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();//大概是输入的字符串转字符数组？Encrypt(stringArr);}public static void Encrypt(char[] arr) {ArrayList<Integer> Resultlist = new ArrayList();for(int i = 0; i < arr.length; ++i) {int result = arr[i] + 64 ^ 32;Resultlist.add(result);}int[] KEY = new int[]{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 j = 0; j < KEY.length; ++j) {KEYList.add(KEY[j]);}//KEYList和KEY的元素完全相同，就是一个是ArrayList<Integer>一个是int数组（？System.out.println("Result:");if (Resultlist.equals(KEYList)) {//Resultlist和KEYList相同System.out.println("Congratulations！");} else {System.err.println("Error！");}}}

唯一有的说的就是那句

int result = arr[i] + 64 ^ 32;

注意加优先级比异或高，逆推得到

arr[i] = (result ^ 32) - 64

写代码！

int a[] = {180, 136, 137, 147, 191, 137, 147, 191, 148, 136, 133, 191, 134, 140, 129, 135, 191, 65};for (int i = 0; i < sizeof(a) / sizeof(int); i++)cout << char((a[i] ^ 32) - 64);