JSB '19 - P3

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Points: 7
Time limit: 5.0s
Memory limit: 64M

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Problem type
Allowed languages
Java

Please call the method flag() in the class Secret.

Download the Java agent here.

Download the source code of the agent here.

You can test locally using the command java -javaagent:p3_agent.jar YourClass.

Source Code

File: Agent.java
import java.lang.instrument.*;
import java.lang.reflect.ReflectPermission;
import java.security.ProtectionDomain;
import java.security.*;

class SecurityIsGood extends RuntimeException {}

public class Agent {
    public static void premain(final String agentArgs, final Instrumentation inst) {
        Thread thread = Thread.currentThread();
        inst.addTransformer(new ClassFileTransformer() {
            @Override
            public byte[] transform(ClassLoader loader, String className, Class<?> classBeingRedefined,
                    ProtectionDomain protectionDomain, byte[] classfileBuffer) throws IllegalClassFormatException {
                if (className.equals("Secret")) {
                    thread.getUncaughtExceptionHandler().uncaughtException(thread, new SecurityIsGood());
                }
                return classfileBuffer;
            }
        });
        thread.setUncaughtExceptionHandler(new Thread.UncaughtExceptionHandler() {
            @Override
            public void uncaughtException(Thread t, Throwable e) {
                if (e instanceof SecurityIsGood) {
                    System.exit(7);
                }
                e.printStackTrace();
                System.exit(1);
            }
        });
        System.setSecurityManager(new SecurityManager());
    }
}
File: Secret.java
public class Secret {
    static public void flag() {
        System.out.println("CTF-00000000000000000000000000000000");
    }
};

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