We keep the key to our holiday cottage in a four-digit key safe by the door. Because of my poor eyesight, I move only one of the digit rotors when I leave, so it is easier to open next time. Most visitors rotate all rotors on leaving. Is my behaviour riskier?
• If all the rotors were scrambled, a would-be intruder would have a one in 10,000 chance of success at each attempt using only trial and error. However, if they guess that only one rotor has been moved, then their chances improve dramatically. The safe-cracker would choose one rotor…
