I was reading this thread and I came up with the following logic:
How do you identify one person?
You have two basic options. Either you test their DNA for a match or you rely on a set of characteristics that will give you a high level of confidence on identifying this person. Characteristics like, full name, address, date of birth, occupation and visual appearance.
Of course the only way to know for sure that your friend is not a reptilian alien with all the right answers is to have his DNA tested.
How do you identify a device?
Androids have no DNA, however we could implement the same kind of logic. Ask the device a few questions and given a high confidence level, proceed to give authorization.
Since it's a slow Sunday, I came up with two diagrams.
Please forgive my paint skilzzz...