especially for reverse

package com.example.user.sirius4;

import android.content.Context;
import android.content.pm.PackageInfo;
import android.content.pm.PackageManager$NameNotFoundException;
import android.content.pm.PackageManager;
import android.os.Bundle;
import android.support.v7.app.AppCompatActivity;
import android.view.View$OnClickListener;
import android.view.View;
import android.widget.TextView;
import java.io.ByteArrayInputStream;
import java.io.InputStream;
import java.security.Key;
import java.security.MessageDigest;
import java.security.NoSuchAlgorithmException;
import java.security.spec.AlgorithmParameterSpec;
import java.util.Arrays;
import javax.crypto.Cipher;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import javax.security.cert.CertificateEncodingException;
import javax.security.cert.X509Certificate;

public class MainActivity extends AppCompatActivity {
    static final byte[] flag;
    static Context mContext;

    static {
        MainActivity.flag = new byte[]{-18, 46, 54, -19, -124, -96, 90, 1, 96, -120, -73, -124, 28, -88, 127, -95, 38, -127, 52, -86, 5, -64, 73, -9, -49, -42, 28, -108, -102, 4, -64, -72};
    }

    public MainActivity() {
        super();
    }

    private static byte[] a() {
        X509Certificate v9_1;
        PackageInfo v4;
        PackageManager v0 = MainActivity.mContext.getPackageManager();
        String v1 = MainActivity.mContext.getPackageName();
        int v2 = 64;
        byte[] v3 = null;
        try {
            v4 = v0.getPackageInfo(v1, v2);
        }
        catch(PackageManager$NameNotFoundException v5) {
            v5.printStackTrace();
        }

        ByteArrayInputStream v7 = new ByteArrayInputStream(v4.signatures[0].toByteArray());
        try {
            v9_1 = X509Certificate.getInstance(((InputStream)v7));
        }
        catch(Exception v9) {
            return v3;
        }

        return MainActivity.b(v9_1);
    }

    private static byte[] b(X509Certificate arg4) {
        byte[] v1;
        byte[] v0 = null;
        try {
            v1 = MessageDigest.getInstance("SHA256").digest(arg4.getEncoded());
        }
        catch(Exception v2) {
            return v0;
        }
        catch(CertificateEncodingException v0_1) {
            v0_1.printStackTrace();
        }
        catch(NoSuchAlgorithmException v0_2) {
            v0_2.printStackTrace();
        }

        return MainActivity.c(v1);
    }

    private static byte[] c(byte[] arg9) {
        int v1 = 100;
        return arg9;
        StackTraceElement[] v0 = v1_1.getStackTrace();
        byte[] v3 = v0[v0.length - 1].getClassName().getBytes();
        int v4;
        for(v4 = 0; v4 < arg9.length; ++v4) {
            int v5 = v3.length;
            int v6;
            for(v6 = 0; v6 < v5; ++v6) {
                arg9[v4] = ((byte)(arg9[v4] ^ v3[v6]));
            }
        }

        return arg9;
    }

    static boolean checkFlag(String arg7) {
        byte[] v0 = MainActivity.a();
        byte[] v1 = new byte[]{-5, -54, 52, -81, -34, 34, -125, 26, -41, 85, -6, -52, -107, -10, -45, 37};
        try {
            IvParameterSpec v2_1 = new IvParameterSpec(v1);
            SecretKeySpec v3 = new SecretKeySpec(v0, "AES");
            Cipher v4 = Cipher.getInstance("AES/CBC/PKCS5PADDING");
            v4.init(1, ((Key)v3), ((AlgorithmParameterSpec)v2_1));
            return Arrays.equals(v4.doFinal(arg7.getBytes("UTF-8")), MainActivity.flag);
        }
        catch(Exception v2) {
            v2.printStackTrace();
            return 0;
        }
    }

    protected void onCreate(Bundle arg3) {
        super.onCreate(arg3);
        this.setContentView(2131296283);
        MainActivity.mContext = this.getApplicationContext();
        MainActivity.a();
        this.findViewById(2131165218).setOnClickListener(new View$OnClickListener() {
            public void onClick(View arg5) {
                String v1 = MainActivity.this.findViewById(2131165239).getText().toString();
                View v2 = MainActivity.this.findViewById(2131165324);
                if(MainActivity.checkFlag(v1)) {
                    ((TextView)v2).setText("Correct! Congrats!");
                }
                else {
                    ((TextView)v2).setText("Wrong! Try harder!");
                }
            }
        });
    }
}