2022picoCTF题目地址

https://play.picoctf.org/practice?category=3&originalEvent=70&page=1

我们下载java程序后打开

一目了然，非常简单，答案已经出来了

源代码分析

import java.io.*;
import java.util.*;  
public class SafeOpener {
    public static void main(String args[]) throws IOException {
        BufferedReader keyboard = new BufferedReader(new InputStreamReader(System.in));
        Base64.Encoder encoder = Base64.getEncoder();                 #使用了base64加密方式
        String encodedkey = "";
        String key = "";
        int i = 0;
        boolean isOpen;
        

        while (i < 3) {
            System.out.print("Enter password for the safe: ");
            key = keyboard.readLine();

            encodedkey = encoder.encodeToString(key.getBytes());
            System.out.println(encodedkey);                           #给我们输入的字符以base64方式加密
              
            isOpen = openSafe(encodedkey);
            if (!isOpen) {
                System.out.println("You have  " + (2 - i) + " attempt(s) left");
                i++;
                continue;
            }
            break;
        }
    }
    
    public static boolean openSafe(String password) {                                    #告诉我们这是flag
        String encodedkey = "cGwzYXMzX2wzdF9tM18xbnQwX3RoM19zYWYz";                      #加密字符，base64解密即可
        
        if (password.equals(encodedkey)) {
            System.out.println("Sesame open");
            return true;
        }
        else {
            System.out.println("Password is incorrect\n");
            return false;
        }
    }
}

flag