Recompiling APK with Google Fit API Issues

Question

I'm attempting to reverse engineer an android app called HeartTrace in order to pull sensor data at a higher frequency. I decompiled, adjusted the parameters, and recompiled the APK. However, the app no longer connects to Google Fit API. Does the API require a new signature from Google before recompiling? If not, what is the issue? Thanks!

Answer 1

As mentioned in Sign Your App,

Android requires that all APKs be digitally signed with a certificate before they can be installed.

Therefore, you need to digitally sign the app again using these two options:

• use the same key which can be found in .keystore file if the app has already been published in apps store, or
• generate a new key to be used in signing in

However, if you opt to use a new key, don't forget to check Signing Considerations.

I highly recommend going through the given documentation wherein these are being discussed in complete details:

• describes how to sign your APKs, including creating and storing your certificate,
• signing different build configurations using different certificates, and
• configuring the build process to sign your APKs automatically.

And for additional information, this tutorial on Google Fit for Android: Reading Sensor Data and solution given in this SO post - Google maps does not work after resigning an apk which is related to decompiling an Android app might also help.