Converting an algorithm from Java to NDK - android

What are the implications for converting a Java algorithm to NDK in order to protect it? This Java algorithm takes data as input and outputs processed data. That's it. It does not interact with the UI in any way.
Will the converted algorithm cause compatibility issues on some of the Android devices?
Since the algorithm is converted to c++, does that mean it cannot be decompiled but can only be disassembled?
Is there any tool that allows me to convert this Java algorithm to NDK without me writing the algorithm myself?
Thank you.

The difference is that Java code is compiled into byte code, which is then run on the JVM, while C/C++ code is compiled into machine code. I don't think it's reasonable to convert Java code to C/C++ because of security reasons, it's mostly done because the code written in C/C++ is much faster.

As far as I know preventing decompilation is one of the main reasons to use NDK along with improving performance as mentioned by Andrej. When it comes to your questions:
1) You will have to make sure you compile your native code for all five supported ABIs, i.e. x86, x86_64, armeabi, armeabi-v7a and arm64-v8a.
2) Nothing is 100% impossible to decompile, but chances that your native code will be successfully decompiled are a lot lower than decompiling java bytecode.
3) No you have to write C or C++ code yourself. However, headers containing the API you want to expose to Java can be generated by javah.
Android Studio makes it quite easy to write small native libraries and integrate them into existing projects, you need only very basic knowledge of CMake.

Related

compile Java to native Android instead of writing in C

We are looking for a way to protect our code and obfuscation is not enough.
Is it possible to compile Android java code to a native Android library?
Another option would be to write the code in c and connect with it through JNI ourselves. But the code we have is quite elaborate and well tested, a rewrite to c would start the testing all over.
PS: Before we were running on x86 hardware and used Excelsior Jet as a means for protection. As we want to move to more cost-effective (cheaper) Arm/android hardware we are looking for a simular solution as Jet, which alas only compiles to x86.
In theory you should be able to use LLVM. It has:
A Java frontend
A C backend
In principle, this could do what you need. However I imagine you'd need to distribute (in compiled form) lots of the Java class library. All in all, it sounds really hard. And someone who really wants to read the code won't have too much problem with ARM disassembly...

Android NDK: can we use C++ for all work

I recently know that we can use Android NDK (use C++ language) to program. But, I'm afraid that, can we use Android NDK to do most of work in Android ? (because people just say that NDK just helps increasing performance of an android program)
I see that ADT plugin for eclipse is powerful, but It's for java. So, if I want to develop on Android NDK, does it has a plugin same with that.
thanks :)
Java is well-supported on Android: there are books, tutorials, Google results and a lot of similar documentation and resources. Developing with the NDK has less stuff available.
Although you can in principle write your full application in C++ using the NativeActivity, I believe that you will have less resources at your disposal for that, compared to Java. If you really want to make your Java program faster, you should profile it, to find which part needs this performance gain and write only that part in C++ using JNI.
you could, but it is not recommend. For one c++ and java performance for multiple aspects are equivalent, then every jni call has its overhead that you have to take in account. Take a look to this link

Decompilation of (binary,NDK) C apps vs. Java apps (Dalvik bytecode)

Well,
since I'm interested in reengineering I spend a lot of time on Android reengineering so far.
Nevertheless I got to a point, where I had the problem of compiled, binary C-Code (NDK) and I got to know that it's very difficult to decompile it back to C/C++ than decompiling a DEX-file back to more or less well Java sources.
What's the reason for this? I mean the bytecode is executed by the Dalvik VM and in case of a usual binary file it's executed by the real processor directly instead. Both are pretty similar except for some additional emulation layers, isn't it? I don't see that much differences at the moment or the reason for this problem.
Do you have any information for me why it's more difficult to decompile a usual binary file (e.g. ELF or MS EXE) back to the C source?
Thanks.
The short answer is that the C/C++ code does not contain any reflective information in it and C/C++ has inline functions, macros, and unrolled loops that the Java compiler just doesn't do (as much as C/C++ compilers do). It is also possible to optimize C/C++ so extensively that all you can do is decompile to assembly because there are no references to the applications own functions. (References to the system's functions will be found though.)
BTW, Hex-Rays ARM Decompiler makes reverse-engineering job much easier, check this out: http://www.hex-rays.com/hexarm_compare0.shtml
The other question is that it costs much...

Running a Haskell program on the Android OS

Forenote: This is an extension of the thread started on /r/haskell
Lets start with the facts:
Android is one awesome Operating System
Haskell is the best programming language on the planet
Therefore, clearly, combining them would make Android development that much better. So essentially I would just like to know how I can write Haskell programs for the Android OS. My question is:
How can I get a Haskell program to execute/run on the Android OS?
How you do it is by first getting a Haskell compiler which can target C with the android NDK which comes with a GCC port for ARM architectures. JHC can trivially do this with a very small inf style file which describes the platform (word size, c-compiler, etc) I've done this with the Wii homebrew dev kit and it was quite easy. However jhc still has some stability issues with complex code such as using a monad transformer stack with IO but jhc has been improving a lot over the last 6 months. There is only one person working on JHC I just wished more people could help him.
The other option is to build an "unregistered" port of GHC targeting the ndk gcc, this is a lot more involved process because GHC is not a true cross-compiler at the moment and you need to understand the build system what parts you need to change. Another option is NHC which can cross-compile to C, like GHC you need to build nhc targeting a C compiler, NHC does not have many Haskell extensions like GHC.
Once you have Haskell compiler targeting NDK GCC, you will need to write bindings to either the android NDK JNI glue code framework (added since android 2.3) or you must write JNI glue code between Java-C-Haskell, the former option is the easier solution and if I remember correctly might actually be backwards compatible with previous versions of Android below 2.3.
Once you have this you must build Haskell code as shared library or static library which gets linked into the NDK java glue code (which itself is a shared library). As far as I'm aware you can not officially run native executables on android. You could probably do it with a rooted phone, thus I assume this means you can not distribute native executables on the app store even when the NDK gcc port can generate native executables just fine. This also probably kills the option for using LLVM unless you can get the NDK JNI working with LLVM.
The biggest hurdle isn't so much of getting a Haskell compiler for android (which is still a big hurdle) the biggest problem is that some one needs to write binding APIs for NDK libraries which is a huge task and the situation is worse if you need to write android UI code because there are no NDK APIs for this part of the android SDK. If you want to do android UI code in Haskell somebody will have to write Haskell bindings to Java through JNI/C. Unless there is a more automated process to writing binding libraries (I know there are some, they are just not automated enough for me) then chances of some one doing it are quite low.
L01man: Is there a tutorial about how to do this? For the
first part, I understand I have to download JHC. What do I have to
write in the inf file and how to use it?
Please note before I answer this question I haven't used jhc for quite sometime since I originally wrote this and newer versions have been released since so I do not know how stable jhc currently is when it comes to code generation of more complex Haskell programs. This is a warning to anyone before you consider making a large Haskell program with JHC, you should do some small tests before you go full on.
jhc does have a manual http://repetae.net/computer/jhc/manual.html and a section on setting-up cross-compilation and .ini file with options: http://repetae.net/computer/jhc/manual.html#crosscompilation.
L01man: The second part is an alternative to the first. I don't know how to do what you said in the
third.
Before you begin you should have some knowledge of C and be comfortable with using the Haskell foreign function interface (FFI) and tools such as hs2c. You should also be familiar with using the Android NDK and building .apk with shared libraries. You will need to know these to interface between C-Haskell, Java/C-Haskell and develop Haskell programs for Android that you can officially distribute/sell on the market store.
L01man: I understand that its goal is to create a binding for the
Android API. But... does the 4th part says we can't make .apk with
Haskell?
.apk is just an app package file format and is built with the tools that come with the Android SDK (not NDK), this has very little to do building the binaries itself. Android packages can contain native shared libraries, this what your Haskell program will be and the native shared/static libraries are generated via the Android NDK.
A language that has recently come to my attention is Eta.
Eta's compiler is a fork of GHC 7.10 which has a JVM backend. It is possible to use the generated JAR files to write Android apps and even use its Foreign Function Interface to call native Android Java libraries.
Brian McKenna has written a blog post about how to configure an Android Studio project to use an Eta library.
There is https://github.com/neurocyte/android-haskell-activity demonstrating Haskell code running.
I once came across the same Reddit thread, but it was old, and comments were closed. I sent a message to the OP, but am not sure whether it reached the recipient. My suggestion here (may work for older Androids where native activities were not possible).
I (developed in Haskell some time ago, but currently switched to Smalltalk) am currently developing a port of Squeak VM to Android. The way I am doing this is similar to what might be dealt with in a haskell-on-android project: a lump of C code which needs to be called from Java part of the application (basically all that can be done in Android is to handle various events; an application cannot poll for events itself and does not have any event loop). In my case the code is generated by the Squeak VM building tools, in the case of haskell on android this will be output from GHC of JHC or whatever front end used. This repo may be worth looking at:
http://gitorious.org/~golubovsky/cogvm/dmg-blessed/trees/master/platforms/android/project
Under "src" there is the Java code which provides for user events interception and sending them to the native code (see the CogView class). The C code of the VM itself is not completely there (see squeakvm.org, the Cog branch for that), but one may get the idea. One also might look under http://gitorious.org/~golubovsky/cogvm/dmg-blessed/trees/master/platforms/android/vm which is the C frontend to the interpreter (including user events handling, some timekeeping, etc.)
Hope this helps.
Dmitry
There is https://github.com/conscell/hugs-android a port of HUGS Haskell interpreter to Android.
I think the general answer should come from source->source transformations, since loading specially compiled shared objects seems to be a bit of a kludge (involving ghc->c and a c->java step in the answers above). This question thus falls under the heading of Haskell on the JVM, which has been tried (with one step as a Java intermediate representation) and discussed at length. You could use frege if the libraries you need compile there. The only remaining steps would be the beginnings of the Android framework API translated into IO() actions and maybe a wrapper for building the manifest xml and apk.

JNI tech. on Android or Linux platform when development ,so?

I face a problem while developing a native C/C++ shared library for Android platform. As we all know that Android use Java language for the upper layer development. Now I have ported my Engine code using ASCII C/C++ to Android using its bionic library, yet when need to design the User Interface, I have to use the JNI to call my engine code.
As far as I know, that is the only choice. The problem is my engine own hundreds of export APIs. If I use the JNI tech. I need to wrap these APIs to a new shared library for use, which will cost a lot of time for development and testing.
Can somebody give some suggestions for this situation? I am not familiar with java or JNI tech by the way.
TIPS:
When I searched the internet, I found some open source for JNI generator such as JNative etc. Until now I do not know is it suitable for Android platform or not.
You can easily use SWIG www.swig.org which will generate the JNI bindings for you.
there is nothing android-specific in that operation, so it will work rather out-of-the-box.

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