Semi-related: I have been reading Ben Macintyre's history of Colditz, the WW2 POW camp. The prisoners used to intercept incoming packages that contained secret

Semi-related: I have been reading Ben Macintyre's history of Colditz, the WW2 POW camp. The prisoners used to intercept incoming packages that contained secret information and tools used for escaping, to remove it before the packages were inspected by the guards. The guards suspected this and enhanced the locks on the mail room. One of the prisoners was a notorious French cat burglar who prided himself in being able to pick any lock. Sure enough, every time the locks were enhanced, he'd learnt how to unlock them within about a week. Some of the details were amazing. The locks were quite advanced, using a four-way set of teeth, each tooth angled in 2D to micrometer precision. And yet, using quite rudimentary tools (often sneaked in in previous packages), he was able to reconstruct keys "borrowed" from unknowing guards. I found it quite amusing, especially as the guards often assumed their security was unbreakable. Heard that one before, lol ...