The master key is generated when you set up your device using your PUK code. For every device, there is only one master key, which is on your phone. If you change phones, delete the application or delete the key, you need to setup the device again with your PUK code to generate a new master key. Important: Do not setup the device on another phone if you want to operate with multiple phones, simply use shared keys for this function.
Shared keys are copies of the master key with various limitations like one-time use and date limits. This means that if you plan to give access to your gate or door to someone else, you need to create a shared key.