dex2jar VS react-native

App tampering and repackaging can be performed by using reverse engineering or tampering tools, such as Apktool, dex2jar, etc.

A week ago I purchased a bluetooth device that takes some measurements. You require an Android or iOS application. The first thing the iOS app did was request permission for your location. Immediate fired up MITMproxy [1] running in transparent `--mode wireguard` and installed it's certificate in the iOS trust store. It was sending a whole bunch of data to China and HK. Since I don't have a jailbroken iPhone, it's off to Android.

For BLE scanning, Android does require permissions for location, but this application is using a Chinese branded tracking SDK and sending encrypted (within already encrypted TLS). So it's time to start reversing and instrumenting the runtime.

Well - not so easy, they used a commercial packer that encrypts their compiled bytecode and decrypts and runs it within a C++ library. I managed to bull the Dalvik out of memory using Frida[2], covert it to java bytecode with dex2jar[3] then into decompiled java with jadx [3].

Since the developer relied on the packer to hide/obfuscate their software, it's quite easy to follow. The libraries that do the location tracking on the otherhand are obfuscated so now I'm at the stage of identifying where to hook before the encrypted blobs are sent to servers in China.

I've sunk about 8 hours into this so far. The message here is that to understand what some applications on your phone does you need to really invest time and effort. The developers increase the cost to the consumer to know what their application is doing by obfuscation, encryption and packing. It's asymmetric.

[1] https://mitmproxy.org/posts/wireguard-mode/

[2] https://frida.re/docs/android/

[3] https://github.com/skylot/jadx

[3] https://github.com/pxb1988/dex2jar

I think they forgot to google translate the disadvantages of JEB Decompiler

I haven't used JEB to comment, but I've gotten a lot of mileage out of https://github.com/pxb1988/dex2jar#readme and then feed the normal Java jars it produces into https://github.com/mstrobel/procyon#readme and (of course) one shouldn't overlook picking your favorite tool for dealing with AndroidManifest.xml which often has fun things hiding in it

While digging up those links, I was reminded that some folks enjoy https://github.com/Konloch/bytecode-viewer#is-there-a-demo because it can be easier to "try out" a few of the decompilation engines, but I don't use it because it's hard to do batch things with it, versus dex2jar into procyon is automation friendly

Take a look at apktool: https://ibotpeaches.github.io/Apktool/ and dex2jar: https://github.com/pxb1988/dex2jar

There was always a tiny sparkle in me telling me that I want to develop mobile apps but I never pursued it. It always felt a bit complicated for me to learn development processes in a completely different industry. I did try developing mobile apps using React Native but it never felt right for me. Also, I already tried to write some Kotlin code and so far I like it, but the whole Android ecosystem is still pretty new to me and I feel there will be a lot to learn. Nevertheless, I will try to learn it in parallel with Elixir but Elixir will be my primary goal, and Kotlin / Android will go along depending on how much time I will have.

This is a modified version of the file from the react native cli template

Recently, there has been a notable shift in mobile application development practices. Rather than creating separate applications for each native platform, many developers are opting for hybrid mobile frameworks like React Native.

React Native [ https://reactnative.dev/ ]

Versatility: JavaScript is not limited to web browsers. It's used in a variety of environments, including mobile app development (using frameworks like React Native), game development (using libraries like Phaser), and even serverless computing (using platforms like AWS Lambda).

In the competitive landscape of mobile app development, user experience (UX) has emerged as a critical differentiator. React Native, with its robust framework and versatile capabilities, offers developers a powerful toolkit to create seamless and engaging user experiences. This blog post delves into the design principles and best practices in React Native app development, uncovering how developers can elevate user experience to new heights and drive success in the digital realm.

You can find the React Native documentation here and Flutter Documentation here.

Additionally, React Native, an extension of React.js, enables developers to create hybrid mobile applications with ease.

You don’t know what to do with your time while applying the 5th rule? Start small, tiny steps. If you can’t read much, start small, 15 minutes a day reading a technical article or even a book like Effective Java, by Joshua Bloch. You don’t like to read? Create small projects by using a framework you want to learn. Check for example: React framework.