Mechanical locks have been developed for thousands of years, and with the development of security access control systems over the years, more and more enterprises and glass turnstiles have begun to use access control systems. Has the security upgraded from mechanical locks to access control systems?
The principle of the mechanical lock is to use the height of each tooth on the key to control the height of the marbles in the lock cylinder, and the lock cylinder can only be turned when all the marbles are at the correct height. Therefore, the saying “one key opens one lock” is not entirely correct. Assuming that there are only 5 tooth positions on a key, and each tooth has 3 different heights (tooth depth / tooth depth), there can only be 35=243 codes at most. That is to say, if you take the door key of your house and open more than 244 door locks of the same model, you will surely open two of them. In common locks, there is also a double-sided key with a 7-digit code (2187 codes), and a cross lock with a 12-digit code (530,000 codes).
There is a term called “reciprocal opening rate”, which refers to how many locks they make can be opened by a key produced by a manufacturer. The higher the mutual opening rate, the less secure the lock is. Therefore, a key with only 5 teeth and only 3 tooth depths on each tooth must have an extremely high mutual opening rate. Think of living in a student apartment at the university, a 6-story building with 30 dormitories on each floor, with a total of 180 rooms. If you use this kind of key with only 243 codes, as long as you try two dormitories, you will definitely open someone else’s door. In fact, the key to my dorm back then could open the door to the dorm across from us.
For companies located in office buildings, access control solutions are usually electronic locks instead of mechanical locks, including access control systems such as door cards, passwords, fingerprints, voice, and face recognition.
Remove the door card and you will see a chip and many coils around it. This chip stores the identity information of the card, such as “I am Anjule”. When the door card is close to the card reader, the electromagnetic waves emitted by the card reader are received by the coil and provide energy to the chip. Then the chip regularly changes the voltage across the door card coil by adjusting the load resistance, which causes a synchronous change in the voltage across the card reader coil, and transmits the information in the chip back to the card reader. Then, the card reader compares this information with the pre-stored information in the database. If this information is pre-registered in the database, then the person is an employee of the company, and the door can be opened. Generally speaking, the information stored in each door card is different from each other, and since it is much easier to add a digit of information to the chip than to add a pin position to a mechanical lock, the information of the door card is usually ten A few decimal digits are enough for hundreds of people on the earth to use together, which theoretically eliminates the phenomenon of “opening each other”.
Has the security upgraded from mechanical locks to access control systems? (figure 1)
So, can access control be copied or cracked? The answer is yes. Under certain conditions, the information in the chip can be rewritten. Depending on the type of card, the difficulty of cracking is also different. Generally speaking, the difficulty of cracking a high-frequency card is much greater than that of a low-frequency card. Because high-frequency cards usually use encryption technology, the information transmitted through electromagnetic waves in the air is ciphertext. Even if you read the ciphertext information with your own card reader, it is useless until it is decrypted. To crack this system, you need a special low-frequency card that can constantly change its output signal, and you can keep trying on the card reader, but this is almost impossible in practice, because it is assumed that each card reading takes 0.1s, Then, if you want to obtain permission through experimentation, you will only be able to try 860,000 numbers a day and a night, and I’m afraid you won’t be able to try more than a dozen numbers until the day the earth stops spinning.
Therefore, the access control system using encrypted key cards is more secure than mechanical locks and more difficult to crack.