The Dangers of the Master Key
That's right, the use of a master key system makes it much simpler to pick any lock in the system. I know I'm going to have to sell you on this one, so here we go.
Let's use the average college dormitory as an example. The typical dorm room has three keys that will open it; the key of the individual rooming there, the Resident Assistant for that area, and the key of the Residential Director for the building. In order for this to work, it means at least some of the pins need multiple key depths that will work. Usually the number of pins for which this is true is kept to a minimum, for reasons that will soon become apparent.
Keys usually have 10 depths, numbered 0-9, to which they can be cut. If there are five pins (the standard for a door), that means there are 10 to the fifth power, or 1000000 possible key combinations, only one of which will work.
Now, in a dorm room key, two of these pins will be set to a single depth, as just described. The other three, however, are set to accept three different depths; one for each key that will accept it. That means that rather than 1 tooth combination that will open the door, there are 29. Now, this may not seem like too much of a big deal, after all, 29 out of 1000000 is still not very good odds. But there are other factors.
When I told you there where 10 possible depths, I was telling the truth, but no the whole truth. While there are 10 depths, only about 7 are usually used. which reduces the possible combinations to 7 to the fifth, or 16807. Quite the reduction. In addition to that, in a college dorm, 2 of these pins are set to the same depth for every key in the building. These two pins can be figured out just by comparing a few keys. This reduces possible key combinations to only 7 to the third, or 343. So now a potential thief has 29 out of 343. Granted, these still aren't good odds, but considering how easy it is to pick a non-mastered lock, such a reduction of odds can make a significant difference.
Let's use the average college dormitory as an example. The typical dorm room has three keys that will open it; the key of the individual rooming there, the Resident Assistant for that area, and the key of the Residential Director for the building. In order for this to work, it means at least some of the pins need multiple key depths that will work. Usually the number of pins for which this is true is kept to a minimum, for reasons that will soon become apparent.
Keys usually have 10 depths, numbered 0-9, to which they can be cut. If there are five pins (the standard for a door), that means there are 10 to the fifth power, or 1000000 possible key combinations, only one of which will work.
Now, in a dorm room key, two of these pins will be set to a single depth, as just described. The other three, however, are set to accept three different depths; one for each key that will accept it. That means that rather than 1 tooth combination that will open the door, there are 29. Now, this may not seem like too much of a big deal, after all, 29 out of 1000000 is still not very good odds. But there are other factors.
When I told you there where 10 possible depths, I was telling the truth, but no the whole truth. While there are 10 depths, only about 7 are usually used. which reduces the possible combinations to 7 to the fifth, or 16807. Quite the reduction. In addition to that, in a college dorm, 2 of these pins are set to the same depth for every key in the building. These two pins can be figured out just by comparing a few keys. This reduces possible key combinations to only 7 to the third, or 343. So now a potential thief has 29 out of 343. Granted, these still aren't good odds, but considering how easy it is to pick a non-mastered lock, such a reduction of odds can make a significant difference.
