PicoGym: Safe Opener#

We are going to solve a playlist in PicoGym called “Safe Opener” today, it consists in 2 challenges written in Java. So, let’s do it!

Safe Opener 1#

The description of the challenge follows:

Can you open this safe?
I forgot the key to my safe but this program is supposed to help me with retrieving the lost key.
Can you help me unlock my safe?
Put the password you recover into the picoCTF flag format like:
picoCTF{password}

After downloading the file named SafeOpener.java, we can read it using the cat command or using any text editor (like notepad or gedit):

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();
        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);

            isOpen = openSafe(encodedkey);
            if (!isOpen) {
                System.out.println("You have  " + (2 - i) + " attempt(s) left");
                i++;
                continue;
            }
            break;
        }
    }

    public static boolean openSafe(String password) {
        String encodedkey = "cGwzYXMzX2wzdF9tM18xbnQwX3RoM19zYWYz";

        if (password.equals(encodedkey)) {
            System.out.println("Sesame open");
            return true;
        }
        else {
            System.out.println("Password is incorrect\n");
            return false;
        }
    }
}

We don’t really need to execute this code, we can check what it does and find the flag.

First we have this line:

Base64.Encoder encoder = Base64.getEncoder();

So, maybe the encoded password is in Base64, and then we can find this line inside the openSafe function:

String encodedkey = "cGwzYXMzX2wzdF9tM18xbnQwX3RoM19zYWYz";

We can make the connection that the encodedkey is our flag, and is encoded in base64.

I will use radare2 to decode this string, but you can use any decoder such as cyberchef.

Using rax2 gives us the flag:

rax2 -D cGwzYXMzX2wzdF9tM18xbnQwX3RoM19zYWYz

And outputs:

pl3as3_l3t_m3_1nt0_th3_saf3

And formatting to the flag structure:

picoCTF{pl3as3_l3t_m3_1nt0_th3_saf3}

Safe Opener 2#

The description of the challenge follows:

What can you do with this file?
I forgot the key to my safe but this file is supposed to help me with retrieving the lost key.
Can you help me unlock my safe?

After downloading the file named SafeOpener.class, we can read it using the cat command or using any text editor (like notepad or gedit):

cat SafeOpener.java

Even though the content is very messy, we can find the flag easily reading through the file.

picoCTF{SAf3_0p3n3rr_y0u_solv3d_it_b427942b}