Krakatau VS Apktool

Since Java bytecode uses MUTF-8, which encodes astral characters as surrogate pairs, I've had to implement this conversion in Python multiple times, in Krakatau and Enjarify.

Not sure how applicable this is for your project since my compiler was written in Python, but I used Krakatau.

Here is one that disassembles the bytecodes and reassembles them https://github.com/Storyyeller/Krakatau .

There's an additional problem that unlike regular assembly or LLVM assembly where there's some fully supported standard format, Jasmin is a third party program and different JVM assemblers and disassemblers disagree on so many things. There are also some newer assemblers and disassemblers like Krakatau you could try instead. Krakatau has different syntax than Jasmin or javap.

Krakatau - Java decompiler and disassembler.

The compiler outputs bytecode in a text format, which can be assembled into .class files using the Krakatau assembler. Figuring out how to translate features like nested functions and nonlocals to JVM was pretty interesting, and having access to Java’s standard library made the whole thing much easier than expected.

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

Apktool made by iBotPeaches, this uses v2.9.1

Can someone clarify what "PP tools" are, and provide a link to them? I came across this link (https://apktool.org/) but I'm not sure if it's the right tool.

Apktool is all you need most of the time.

But it'll still be editable and we can make something good out of it. One of the famous ones, that I'm planning to use is ApkTool(https://ibotpeaches.github.io/Apktool/).

I did a dissection of twitter apk (got from apk pure) with apktool, and I found permission :

Not sure. I started reverse engineering Java apps very early in my life — initially it was J2ME games. Decompilers of the time sucked but that didn't stop me from modding Gravity Defied :P

I honestly don't know what's a good way of getting started on reverse engineering. There's a bunch of everything about Windows executables in particular, including "crackmes", but native machine code is a level up from JVM bytecode. Java classes and Android dex files can be decompiled back to sensible source with a good chance that you get something that can be compiled again. No such luck for native code — C/C++ compilation is a lossy process by its nature, especially the optimizations. Ghidra does a decent job but still requires a non-zero amount of manual assistance. Flash games also were good to hone one's reverse engineering skills since ActionScript decompilers did a pretty darn good job.

Anyway. To decompile dex to Java source, there's jadx: https://github.com/skylot/jadx

Since decompilation is sometimes lossy, there's apktool for when you want to put the app back together after tinkering with it: https://github.com/iBotPeaches/Apktool

It goes without saying that you also need a JDK and the Android SDK. In particular, you need apksigner form the SDK to sign the unsigned apks generated by apktool. You can also automate things a bit and use adb to deploy them to your device.

What I usually do is get a high-level overview of the app in jadx, and then modify the smali (dalvik bytecode in text form, very assembly-like) files generated by apktool.

I am not game or android app dev, but you might first need to de-compile apk using tools like https://ibotpeaches.github.io/Apktool/