I am resigning apps on a system image in a manner similar to : Resigning System Image on a Device.

What I am trying to figure out is how Android verify these apks. In the standard android build the platform cert is selfsigned: platform.x509.pem. I guess and hope this certificate is deployed as a file somewhere on the device.

For instance in my test system image framework-res.apk is signed with a selfsigned certificate with the serial number d20995a79c0daad6 but this certificate is no where to be found in /system/etc/security/cacerts.

My question is how is the platform certificate known to Android assuming it is not hardocded somewhere.

EDIT #1: I pasted the subject key id instead of the serial number.

EDIT #2: I searched the entire image for PEM encoded certificates, found some but still no platform cert. Searched for the DER encoding of the serial number too but without luck.


I was finally able to identify and ultimately change the platform certificate on an emulator and a test device by patching the following files:


  • Contains a hexdump of the DER encoded platform certificate
  • Contains the PEM encoded public key of the platform certificate


  • Contains a hexdump of the DER encoded platform certificate

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.