I\'m trying to publish my app to Google playstore, and I can not figure out how to sign the app use the upload key, as stated in https://developer.android.com/studio/publish
With the new system, the upload key is a simple and normal keystore which you can create with android studio.
So, juste sign your apk, et send it to playstore.
Google will remove this key, and use the application key declared (and generated in google play)