SCTF ANDROID CHAL SOL 1

a.java

package com.x64mayhem;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.IvParameterSpec;
import javax.crypto.spec.SecretKeySpec;
import java.security.InvalidAlgorithmParameterException;
import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

public class a {
    public static byte[] f821a; //THIS VAR GETS THE KEY
    public static byte[] a(byte[] bArr) {
        //DECRYPT
        Class<a> cls = a.class;
        try { 
            Cipher AESCBC = Cipher.getInstance("AES/CBC/PKCS5Padding");
            SecretKeySpec keyspec = new SecretKeySpec((byte[]) cls.getDeclaredFields()[0].get(null), "AES");
            IvParameterSpec IVSPEC = new IvParameterSpec((byte[]) cls.getDeclaredFields()[0].get(null));
            AESCBC.init(Cipher.DECRYPT_MODE, keyspec, IVSPEC);
            return (byte[]) AESCBC.doFinal(bArr);
            
            } catch (NoSuchPaddingException ex) {
            ex.printStackTrace();} catch (NoSuchAlgorithmException ex) {
            ex.printStackTrace();} catch (InvalidAlgorithmParameterException ex) {
            ex.printStackTrace();} catch (InvalidKeyException ex) {
            ex.printStackTrace();} catch (BadPaddingException ex) {
            ex.printStackTrace();} catch (IllegalBlockSizeException ex) {
            ex.printStackTrace();} catch (IllegalAccessException e) {e.printStackTrace();}
return null;}}