Removing Certificate Pinning from Pokemon Go Without Going Native

What is up?

Today we’re removing certificate pinning from Pokemon Go to man-in-the-middle the connection between my phone and the server, which is now required.

Main difference from similar posts, such as Eaton’s method where he removes it from the native code, is that, we’re not stepping to the dark side, and the main reason for that, for me, its much easier to patch the applications Dalvik code than the native ARM code, and I don’t feel too comfortable poking around in the native code, also I don’t have the tool required, Ida Pro with ARM..

Anyway! Lets get to the real deal, right!

First step, we need to take apart the APK, which is simple! Just use your favourite APK Extractor from Google Play, dump the APK on your machine and use APK Tools to unpack it.

Where apktool_2.1.1.jar is your flavour of APK tool and pokemon_original.apk is the APK dumped from your device.

After that we have a folder containing all the files, good to modify!

Logically we make our way through niantic packages, com/nianticlabs/nia/network sounds good, right?

In this package we find a NianticTrustManager.smali, so its time to fire up your favorite text editor, you can use any, but please don’t use Notepad, its pain in the ass to read..

Given the name too, its clear that this Class implements X509TrustManager, which is as the name says, responsible for the trust management. So its time to lose the trust, right?

Because I’ve poked around with this before, I know how to overcome this slight problem, we’ll have just to return a null from getAcceptedIssuers() and do nothing in checkClientTrusted() and checkServerTrusted()

We take roughly our handle of the latter two methods and remove all the code, leaving behind this kind of structure.

And in the getAcceptedIssuers() we have to actually write some code, meh.. Shouldn’t be too hard!

So we just assign v0 a null(0) and return it with no further ado

Okay, I think we are ready.. Lets cross our fingers and put together this goodness!

First we build the apk from the folder that contains all the files, meaning the pokemon folder!

Then we need to get a keystore from somewhere, which will be used for signing, creating that is quite simple, just run the keytool!

After that we’re left with a key that is used to sign the actual apk using jarsigner!

This creates a pokemon_ua.apk file. ua stands for Un-Aligned, if you’re into Android Dev, you might now that the apks needs to be aligned before shipping! Which is a matter of running a zipalign on them, which is also described in the manual signing process article.

And finally we got the final ‘release’ build! Lets shove that into our device! Make sure you uninstall previous installations of the app!

Run the app on the device, throw in your age, sign in aaand… In like a flynn!

Open up your favorite MITM proxy, such as Charles, which is what I am going to use, and configure your device to connect to the proxy instead, continue using the app and you will see what will make angels hum.

result

 

 

 

There we go, unencrypted version of the packets! However this is in a undecoded protocol buffer, which descriptor you can probably find online.. In Github or somewhere..!

Reversing Bytecode That Your Avarage Decompiler Can’t Handle By Hand

Hello guys, long time no crocodile, or how did it go, huh? Meaning, haven’t written here for too long.. Enough excuses!

Recently I was facing a problem, regarding taking a screenshot in Android programmatically, without falling back on unsupported API’s meaning, using the MediaProjection API’s introduced in API level 21, however, the actual problem I had, following their official examples or those of third party ones is a subject for another blog post!

Today we are covering, yet again, reverse engineering of a proven working application, this time, not for abuse of virtual benefits, but to copy a working functionality from a third party app, not in line by line manner, but in a overall concept, to avoid any copyright related takedowns.

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IANAL but not that these kind of small companies have any power to pursue such or take down every app that uses similar technology to compare the code, but you can never be too sure or secure, or have too much moral to secure nightsleep.

Fun fact, the app I broke down seems to actually have a class leeched from rival application.

I wouldn’t have noticed, if they hadn’t kept the exact same package name as the rival application is released under.. Smart..

Initial steps I took to figure what I was doing wrong with the MediaProjection, to only receive the black screen, was ofcourse to find one application that does screencapture from service or such, that’s available in Google Play currently, and there’s plenty, not to name any, not that I am going to release a screenshotting application for now..

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When I first found one I obviously put it through my favorite set of Android reverse engineering tools, which of easiest and quickest is bytecode viewer, big shootout for them, the UX is crap, but its for me, the easiest way to drop an APK in and receive both bytecode and human readable version of the code inside, and not even talking about the search tools, which are hard to use, but useful!

To my disappointment after finally finding the reference to the API I knew the app was using, due to the Android’s forced dialogue of giving app permission of capturing the screen, the decompiler were unable to reverse the bytecode due to the complicated branching or whatever.

After that I looked at the bytecode, that spanned across maybe 200 lines and ran it through in my head, couldn’t initially figure the difference between it and my rough implementation that I had partially scrapped from the API example, but for one, there was 500 ms sleep in added in the code, I tried adding it between same API calls, but no luck.. We had to go deeper!

Before digging deeper and spending all my time just to find out I am looking at wrong piece of code, as the application had what, 20 ways of capturing a screenshot, to support some legacy phones that I wasn’t looking to support, I copied baldly the .smali files, containing the dalvik code, to my own project, after ‘baksmaling’ it using apktool, and added a quick call to the function, which worked flawlessy and resulted in good looking screenshot, I was ready to proceed with the reverse engineering efforts!

I tried another decompiler or two, with no luck, hard to tell what it is, that breaks the decompiler, and I am not too much into those anyway, I started writing the code by hand, following the Dalvik code on my other screen.

If you’re not a robot or a machine in any other way, it will be pretty hard to go through so many lines of bytecode and getting the grasp of what’s happening without spending countless of hours on it.

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I found its much easier to implement the logic in other language or even in pseudo code, for the ease of my brains, which has the most working paths of understanding Java, I did it in java, which is good, as it is the final language I am going the feature to implement in, even tough, implementing all the branches which are implemented in dalvik using labels, gotos and conditionals might get pretty tedious, after having it all written down, it will be easy to refactor it for real world use!

Lets look at an example!

This isn’t too complicated, but if you have to stitch tens of this size patches of code in your mind, it gets pretty hard..

A quick rundown of above code in pseudo code for comparison

This is not(IIRC) not part of the applications code, but part of the code I used to find out which parameters the reverse engineered app passes to the function

As you can see, a small piece of java goodness turns into crazy amount of bytecode, and without even including the conditionals with all the labels, don’t even let me get into that part!

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Round of applause for the findings

TL/DR
When reverse engineering bytecode your decompiler or other tool can’t handle, and its too overwhelming, just write it down in pseudo code or in your favorite language to give your brains a break!