Not sure what you are referring to exactly, but Android on the phone only supports signing by one specific key. In the Play Store signing scheme, Google verifie

Not sure what you are referring to exactly, but Android on the phone only supports signing by one specific key. In the Play Store signing scheme, Google verifies the publisher by requiring that you sign the app first with a specific "upload key". Google then replaces (not co-signs) this with a key they control, and the handset verifies only against this Google-controlled key. For apps not enrolled in the Play Store signing scheme, the phone actually verifies directly against the publisher's key, that Google now wants to relegate just as an "upload key". I am saddened by Google's efforts to undermine this fundamental OS security feature. The ultimate goal is clearly to kill off any chance of competing app stores, as developers of new apps distributed through Play Store can now actually never access the key that's supposed to show they control the app, no matter what channel it was delivered through (e.g. Play Store vs. F-Droid.. Really bad for new Open Source apps!)