# Coding

Work in progress
Tuesday, April 28, 2020

DummyDroid won't download APK files when mocking a Lineage OS device (or any custom ROM for that matter)

With Android and Play, figuring out device compatibility is somewhat of a black art. Which really just is a nice way for saying 'the whole Android ecosystem is one giant compatibility hack'.

Thursday, March 5, 2020

Ha! Fun! When you ask Google Play for anything, you get a binary blob in response which must be parsed, using the protobuf library. There are two version of that library available (v2.x and v3.x) that implement version 2 and 3 of the protocol buffer language respectively. Since the two languages are incompatible with each other, I always assumed that the libraries would be as well, but that’s not the case! Version 3.x of the library is actually backwards compatible and able to properly handle blobs created with v2.x!

Why is this so great? Well, Play is inherently tied to version 2 of the language, but the v2.x library lacks a lot of useful features, such as the ability to export a binary blob to JSON. You can only format a message as plain text which kinda looks like JSON, but won’t be parseable. For small stuff that’s sufficient, but you are completely at a loss when dealing with something bigger, such as search results.

So, here’s the same search result (“test”) in the plain text and in the json format. The later can easily be inspected in existing tools (Firefox for example).

Tuesday, February 25, 2020

Preview: Dummydroid 2.0 - The new app compatibility checker and GSF ID generator

We all know the problem: Google Play only allows us to download apps, compatible with our device and accessible from our current location. Well, that can be helped.

Thursday, February 20, 2020

Hm, a lot of people come to the blog lately, looking for a split APK merge tool. I actually just had an idea how to make one. The stupid thing just is that it would not work on Android versions that don’t support App Bundles, so I don’t quite see the point.

Tuesday, February 18, 2020

Does anyone have a cool idea what to do with the wishlist feature on Google Play? Technically it’s just a bookmarklist for digital goods (works for apps, music, books, …) that have a store page. Seems like a shame to implement it the way it was intended to be used (as a self imposed pester power item).

Made a bit of progress on the bypass sms verification code when signing up for a new Google account. The whole system is breathtaking from a technical, legal as well as a psychological persepective.

At least on Android, the user is deliberately steered into a “sunk cost falacy” type of situation that suggests that s/he just wasted a couple hundred bucks on a toy that won’t work properly unless connected with a Google Account. Of course, the phone screen is too small to read the terms compfortably and the default is to skip reading your contract anyway. If you want to know what you actually agree to, you pretty much have to look at the wire protocol (it is a lot). How on earth is it that we don’t have laws against this?!

Friday, February 14, 2020

Of course, DummyDroid is pretty much unfixable for various reasons. It’s cheaper/faster to rewrite it from scratch. The main problem here is that in order to spoof an Android device, you need to supply 29 data points:

  • From 📁 /system/build.prop : manufacturer, brand, device, hardware, product, model, id, fingerprint, releaseversion, sdk version, bootloader, abi list.
  • Open GL version and list of supported extensions.
  • Supported locales
  • Obsolete stuff: support for hardware keyboard, 5 way nav input and touchscreen type.
  • Screen layout, size, density
  • Installed libraries
  • List of system available features (e.g. bluetooth, sensors, …)
  • List of installes shared libraries
  • Version information of certain important apps (com.android.vending).
  • Other nonsense: timestamps, OTA installed

Some items (e.g. fingerprint, timestamps, locales) can be calculated or set to sane defaults, but that still leaves around 20 things that must be collected by the user. The challenge is coming up with a userfriendly interface for that.

Thursday, February 13, 2020

K, Google came up with a new shitty idea to make sideloading difficult: uncompressed native libraries in the APK. The story here is that it will save space on the device if native libraries don’t have to be extracted, but can directly be mapped from inside the APK file. So now we are in the happy situation, that based on the SDK version (or more precisely: the version of the finsky app), we can get the very same app in three different variants:

  • As a traditional, “contains everything and the kitchensink” APK.
  • As an app bundle consisting of several APK modules
  • As an app bundle consisting of several APK modules where the native code module contains uncompressed files.

Well, it’s not an immediate problem with Raccoon, but I should probably focus on fixing DummyDroid now.

Wednesday, February 5, 2020

Finally done! Raccoon v4.12 should solve the CAPTCHA issue. Next stop: rewriting/replacing DummyDroid.

Tuesday, February 4, 2020

Done! Bouncycastle does the trick. The rest is a diligent but routine piece of work. Should take only a few more days.