I stumbled on this page after reading Matt Blaze's legendary paper about deducing master keys from physically strong, but cryptographically weak, physical systems.
The paper is really good, and worth a read, even though it is from 2003:
The paper is really good, and worth a read, even though it is from 2003:
There are master keyed systems that don't have that combinatoric weakness. Here's the Lock Picking Lawyer disassembling a prison lock where there's a separate "master ring" for the master key. So combining settings from the master key and the operating key will not open the lock.
This lock was opened with a wave rake, though, so it's not very good.