Safe_Opener_2.md

Safe Opener 2

• Challenge information
• Grepping for the flag solution
• Decompiling with JD-GUI solution
• References

Challenge information

Points: 100
Tags: picoCTF 2023, Reverse Engineering
Author: MUBARAK MIKAIL
 
Description:
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?
 
Hints:
1. Download and try to decompile the file.

Challenge link: https://play.picoctf.org/practice/challenge/375

There are several ways to solve this challenge. Here are two solutions presented in increasing difficulty.

Grepping for the flag solution

On easy challenges it's always recommended to search for the flag in plain text with strings and grep.

┌──(kali㉿kali)-[/picoCTF/picoCTF_2023/Reverse_Engineering/Safe_Opener_2]
└─$ strings -a -n 8 SafeOpener.class | grep picoCTF
,picoCTF{<REDACTED>}

Decompiling with JD-GUI solution

A more sofisticated solution is to decompile the file in JD-GUI and study the code.

You find the flag in the openSafe function (but it's redacted here).

  public static boolean openSafe(String password)
  {
    String encodedkey = "picoCTF{<REDACTED>}";
    if (password.equals(encodedkey))
    {
      System.out.println("Sesame open");
      return true;
    }
    System.out.println("Password is incorrect\n");
    return false;
  }

For additional information, please see the references below.

References

• JD-GUI - GitHub
• grep - Linux manual page
• strings - Linux manual page