A rather widespread rumour tells of how the owners of a famous car, produced by a well known Italian car manufacturer in the 1980s, which was very often white in colour, often opened by mistake someone else’s car with their own key, when confusing it with their own car in a parking lot, maybe when leaving the cinema or a concert.
Maybe it is just an urban myth, but it does make one reflect on an important security issue: how many different keys exist for a given lock? In other words, what is the probability that a person in possession of a key can open another lock of the same type, as well as their own? This is not just a mere curiosity. There are situations in which this can actually happen. For example, there are dozens of mailboxes with the same lock in a large condominium: is it possible that a key can open more than one? Continue reading →