# droids1

## Problem

> Find the pass, get the flag. Check out this file. You can also find the file in /problems/droids1\_0\_b7f94e21c7e45e6604972f9bc3f50e24.

* [APK File](https://github.com/HHousen/PicoCTF-2019/tree/24b0981c72638c12f9a8572f81e1abbcf8de306d/Reverse%20Engineering/droids1/one.apk)

## Solution

1. Decompile the APK using [apktool](https://ibotpeaches.github.io/Apktool), as suggested by the hint: `apktool d one.apk`:

   ```
    Picked up _JAVA_OPTIONS: -Dawt.useSystemAAFontSettings=on -Dswing.aatext=true
    I: Using Apktool 2.4.1-dirty on one.apk
    I: Loading resource table...
    I: Decoding AndroidManifest.xml with resources...
    I: Loading resource table from file: /home/kali/.local/share/apktool/framework/1.apk
    I: Regular manifest package...
    I: Decoding file-resources...
    I: Decoding values */* XMLs...
    I: Baksmaling classes.dex...
    I: Copying assets and libs...
    I: Copying unknown files...
    I: Copying original files...
   ```

   Alternatively, you can use [JADX](https://github.com/skylot/jadx) to decompile and look around in a GUI. This is the method used in this write-up.

   JADX Install:

   ```
    wget https://github.com/skylot/jadx/releases/download/v1.1.0/jadx-1.1.0.zip
    unzip jadx-1.1.0.zip -d jadx
    cd jadx
    sudo mkdir /opt/jadx
    sudo mv * /opt/jadx
    cd /opt/jadx/bin
    ./jadx-gui
   ```
2. Launch `jadx-gui` and open `one.apk`
3. In the `MainActivity` the button click code can be seen:

   ```java
    public void buttonClick(View view) {
        this.text_bottom.setText(FlagstaffHill.getFlag(this.text_input.getText().toString(), this.ctx));
    }
   ```
4. The `getFlag()` function is as follows:

   ```java
    public static String getFlag(String input, Context ctx) {
        if (input.equals(ctx.getString(R.string.password))) {
            return fenugreek(input);
        }
        return "NOPE";
    }
   ```

   It checks if the input is `R.string.password`, and if it matches then the flag is shown.
5. Go to `R > string > password` in the explorer to find `public static final int password = 2131427375;`. It is accessing resource \`2131427375.
6. Go to `Resources > resources.arsc > res > values > strings.xml` since the password is probably a string. We find: `<string name="password">opossum</string>`
7. Start an AVD in [Android Studio](https://developer.android.com/studio). Install the app by dragging the APK to the emulator. Enter the password, `opossum`, and click the button to get the flag. ![Screenshot of the app with flag output](/files/-MZKDR5Fv9G0g3vKoCuf)

### Flag

`picoCTF{pining.for.the.fjords}`


---

# Agent Instructions: Querying This Documentation

If you need additional information that is not directly available in this page, you can query the documentation dynamically by asking a question.

Perform an HTTP GET request on the current page URL with the `ask` query parameter:

```
GET https://picoctf2019.haydenhousen.com/reverse-engineering/droids1.md?ask=<question>
```

The question should be specific, self-contained, and written in natural language.
The response will contain a direct answer to the question and relevant excerpts and sources from the documentation.

Use this mechanism when the answer is not explicitly present in the current page, you need clarification or additional context, or you want to retrieve related documentation sections.