JSB '19 - P2

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Points: 7
Time limit: 2.5s
Memory limit: 64M

Problem type
Allowed languages

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:p2_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 Secret {
    private void flag() {

public class Agent {
    public static void premain(final String agentArgs, final Instrumentation inst) {
        System.setSecurityManager(new SecurityManager() {
            public void checkPermission(Permission perm) {
                if (perm instanceof ReflectPermission) {
                    Class[] ctx = getClassContext();
                    // allow non-submitted classes to use reflection
                    if (ctx[ctx.length - 1].getPackage() == null) {


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