[GeekyBear]

> even ancient systems are still allowed to log into icloud, and those ancient systems didn't do any cryptography so all you need is a valid serial number that nobody else is using

The ancient random serial numbers are also in a standard format.

> Apple devices manufactured after 2010 generally have 12-character alphanumeric serial numbers, with the first three digits representing the manufacturing location, the following two indicating the year and week of manufacture, the next three digits providing a unique identifier, and the last four digits representing the model number.