Bunker

You reach a large metal door. It’s protected by large yellow bars. There appears to be an panel with a keypad…

We’re given a .jar file to reverse. JADX is a great tool for doing exactly that. I’m personally using the GUI version of JADX.

This is the only Java file in the JADX decompilation:

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package defpackage;
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import java.awt.Component;
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import java.awt.event.ActionEvent;
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import java.awt.event.ActionListener;
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import javax.swing.JButton;
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import javax.swing.JFrame;
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import javax.swing.JOptionPane;
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import javax.swing.JPanel;
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import javax.swing.JTextField;
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import javax.swing.UIManager;
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/* compiled from: bunker.java */
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/* renamed from: Bunker  reason: default package */
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/* loaded from: Bunker.jar:Bunker.class */
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class Bunker extends JFrame implements ActionListener {
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    static JFrame f;
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    static JTextField l;
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    String output = "";
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    Bunker() {
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    }
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    public static void main(String[] strArr) {
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        f = new JFrame("Bunker");
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        try {
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            UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
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        } catch (Exception e) {
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            System.err.println(e.getMessage());
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        }
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        Bunker bunker = new Bunker();
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        l = new JTextField(8);
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        l.setEditable(false);
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        JButton jButton = new JButton("0");
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        JButton jButton2 = new JButton("1");
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        JButton jButton3 = new JButton("2");
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        JButton jButton4 = new JButton("3");
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        JButton jButton5 = new JButton("4");
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        JButton jButton6 = new JButton("5");
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        JButton jButton7 = new JButton("6");
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        JButton jButton8 = new JButton("7");
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        JButton jButton9 = new JButton("8");
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        JButton jButton10 = new JButton("9");
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        JPanel jPanel = new JPanel();
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        jButton.addActionListener(bunker);
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        jButton2.addActionListener(bunker);
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        jButton3.addActionListener(bunker);
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        jButton4.addActionListener(bunker);
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        jButton5.addActionListener(bunker);
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        jButton6.addActionListener(bunker);
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        jButton7.addActionListener(bunker);
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        jButton8.addActionListener(bunker);
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        jButton9.addActionListener(bunker);
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        jButton10.addActionListener(bunker);
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        jPanel.add(l);
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        jPanel.add(jButton);
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        jPanel.add(jButton2);
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        jPanel.add(jButton3);
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        jPanel.add(jButton4);
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        jPanel.add(jButton5);
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        jPanel.add(jButton6);
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        jPanel.add(jButton7);
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        jPanel.add(jButton8);
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        jPanel.add(jButton9);
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        jPanel.add(jButton10);
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        f.add(jPanel);
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        f.setSize(120, 500);
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        f.show();
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    }
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    public void actionPerformed(ActionEvent actionEvent) {
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        this.output += actionEvent.getActionCommand();
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        l.setText(this.output);
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        if (this.output.length() == 8) {
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            System.err.print("USER ENTERED: ");
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            System.err.println(this.output);
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            l.setText("");
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            if (this.output.equals("72945810")) {
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                StringBuilder sb = new StringBuilder();
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                for (int i = 0; i < "Q^XSNZD^\\WKk\u0004\tnCVKJkTOPYCm_AGLYUEmPZFLCETFP[[E".length(); i++) {
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                    sb.append((char) ("Q^XSNZD^\\WKk\u0004\tnCVKJkTOPYCm_AGLYUEmPZFLCETFP[[E".charAt(i) ^ this.output.charAt(i % this.output.length())));
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                }
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                JOptionPane.showMessageDialog((Component) null, sb.toString());
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            } else {
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                JOptionPane.showMessageDialog((Component) null, "=== BUNKER CODE INVALID ===");
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            }
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            this.output = "";
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        }
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    }
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}

Seems like the code is just 72945810.

Run the program with java -jar Bunker.jar and input the code into the numeric keypad to get the flag!

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flag{bunker_11_says_await_further_instruction}