Unfold the secret, from: https://mas.owasp.org/crackmes/Android/#android-uncrackable-l1

UncrackableApp1Test.java

import android.util.Base64;

import androidx.test.ext.junit.runners.AndroidJUnit4;

import org.junit.Test;
import org.junit.runner.RunWith;

import java.security.InvalidKeyException;
import java.security.NoSuchAlgorithmException;

import javax.crypto.BadPaddingException;
import javax.crypto.Cipher;
import javax.crypto.IllegalBlockSizeException;
import javax.crypto.NoSuchPaddingException;
import javax.crypto.spec.SecretKeySpec;

/**
 * Created by mzennis on 16/12/2024
 */
@RunWith(AndroidJUnit4.class)
public class UncrackableApp1Test {

    @Test
    public void unfoldTheSecretT()
            throws NoSuchPaddingException, IllegalBlockSizeException,
            NoSuchAlgorithmException, BadPaddingException, InvalidKeyException
    {

        byte[] firstArg = b("8d127684cbc37c17616d806cf50473cc"); // secret key
        byte[] secondArg = Base64.decode("5UJiFctbmgbDoLXmpL12mkno8HT4Lv8dlat8FxR2GOc=", 0);

        System.out.println(
                new String(
                        a(firstArg, secondArg) // put all together
                )
        );
    }

    public static byte[] a(byte[] bArr, byte[] bArr2)
            throws NoSuchPaddingException, NoSuchAlgorithmException,
            InvalidKeyException, IllegalBlockSizeException, BadPaddingException
    {
        SecretKeySpec secretKeySpec = new SecretKeySpec(bArr, "AES/ECB/PKCS7Padding");
        Cipher cipher = Cipher.getInstance("AES");
        cipher.init(2, secretKeySpec);
        return cipher.doFinal(bArr2);
    }

    public static byte[] b(String str) {
        int length = str.length();
        byte[] bArr = new byte[length / 2];
        for (int i = 0; i < length; i += 2) {
            bArr[i / 2] = (byte) ((Character.digit(str.charAt(i), 16) << 4) + Character.digit(str.charAt(i + 1), 16));
        }
        return bArr;
    }
}