From mechanical lock to access control system, is

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From mechanical lock to access control system: is your door lock safe

mechanical locks have been developed for thousands of years. Now almost all the door locks used by every household are mechanical marble locks, which are still the technology of the mid-19th century in principle

The principle of

marble lock is to use the height of each tooth on the key to control the height of the marble in the lock cylinder. When all the marbles are at the correct height, the lock cylinder can be turned. Therefore, the saying that one key opens one lock is not completely correct

(the picture comes from the network)

suppose that one should give the car the position of only five teeth on the "weight loss" key under the condition of ensuring safety and performance, and each tooth has three different heights (tooth depth/tooth depth), so there can only be 35=243 codes at most. In other words, if you take your door key and open more than 244 locks of the same type, you will certainly open two. In common locks, there is also a 7-bit coded double-sided key (2187 codes) and a 12 bit coded cross lock (530000 codes)

there is a term called mutual opening rate, which refers to how many locks can be opened by the keys produced by a manufacturer. The higher the mutual opening rate, the worse the security of this lock. Therefore, there are only five teeth, and each tooth has only three tooth flower depths. The mutual opening rate must be extremely high

(the picture is from the network)

I want to live in the student apartment of the University, a 6-story building with 30 dormitories on each floor, a total of 180 rooms. If you use this key with only 243 codes, as long as you try two dormitories, you will definitely open someone else's door. In fact, the key of my dormitory used to open the door of the dormitory opposite us

How do you unlock it when you lose the key

you have two choices

if you master the unlocking skill, you can easily open this kind of marble lock with wire or hairpin. In 1992, geek, whose pseudonym was ted the tool, wrote a pamphlet about the structure of the marble lock and how to unlock it while reading at MIT, and named it the MIT lockpicking guide 1, which was widely circulated all over the world

according to this pamphlet, the reason why the marble lock can be opened with a hairpin is that some inevitable small errors in the mechanical structure of the marble lock are used. First, apply a torque to the marble lock with something like a screwdriver. Due to mechanical error, not all marbles can be stuck at the same time, but only one marbles will be stuck. Then pull the marble back and forth with the hairpin. Once the stuck marble is pushed to the correct position, the torque applied by the screwdriver will make the lock cylinder rotate a small angle until another marble is stuck. Repeat this step. When all the marbles are pushed to the right position, you will unlock successfully

(the picture comes from the network)

but this method needs some training to be used in practice. There is another method that allows untrained ordinary people to open part of the lock. This method is called hitting the key. A Danish locksmith accidentally found that by gently hitting the key inserted in the lock, all the marbles would jump out together. If you grasp the opportunity, you can open the door

Figure 18 schematic diagram of unlocking the marble lock

according to this principle, the German locksmith made a special key with the deepest tooth flower depth. Insert this key into the lock, and all the marbles will fall. At this time, if you slap the key with appropriate strength, it may cause all the marbles to jump together briefly and open the door

in 2006, the toool unlocking Association, headquartered in the Netherlands, tested 60 marble locks on the European market. Using the method of bumping keys, untrained ordinary people can open 35% of the locks, while experienced locksmiths can open 78% of the locks in 3 minutes. So if you want to open the door in this way, you have to get a master key like this

(picture from the network)

in fact, China issued a lock standard in 1994, which divided the safety level of locks into two levels: A and B. The locks that can be opened by this method are class a locks, while the safer class B locks have deeper teeth, more digits, and the use of magnetic beads instead of steel marbles, which increase the difficulty of unlocking. Note that the AB key of the door will be involved in the decoration, which means that once the key (householder key) has been used to open the door in the process of the B key experiment, the a key (decoration key) cannot be used to open the door, which is completely different from the B-level lock

can the door card be cracked

for companies located in office buildings, access control solutions are usually electronic locks rather than mechanical locks, including door cards, passwords, fingerprints, sounds, face recognition, etc. The most popular electronic lock system is RFID door card

now that we talk about RFID door cards, let's first explain what RFID is. RFID is the abbreviation of radio frequency identification. Its core technology is developed by Philips

(the picture comes from the network)

take apart the RFID door card, and you will see a chip and many coils around it. This chip stores the identity information of the card, such as my door card

when the RFID door card is close to the card reader, the electromagnetic wave emitted by the card reader is received by the coil to provide energy to the chip. Then the chip regularly changes the voltage at both ends of the door card coil by adjusting the load resistance, which causes the synchronous change of the voltage at both ends of 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 information pre stored in the database. If this information is pre registered in the database, then this person is an employee of the company and can open the door for release. Generally speaking, the information stored in each door card is different from each other, and because it is much easier to add one digit of information in the chip than to add a bullet position in the mechanical lock, the information of the door card is usually a dozen decimal digits, which is enough for hundreds of people on earth to use together, which theoretically eliminates the phenomenon of mutual opening

(the picture comes from the network)

then, can RFID access control be copied or cracked? Yes. Under certain conditions, the information in the chip can be rewritten; The difficulty of cracking varies according to the type of card. Common RFID cards have two frequencies, low-frequency 125kHz (the most common and popular door card system in China) and high-frequency 13.56MHz (bus card/subway card). Generally speaking, the cracking difficulty of high-frequency cards is much greater than that of 125kHz low-frequency cards, because high-frequency cards usually use encryption technology. The information transmitted through electromagnetic waves in the air is ciphertext. Even if you read this ciphertext information with your own card reader, it is useless before decrypting it

low frequency gate cards are usually very easy to copy because they are usually not encrypted

(the picture comes from the network)

when a low-frequency door card gets energy from the card reader, it keeps calling my number is. Therefore, if you have a low-frequency RFID door card of the community and want to copy one to your roommate, you only need a card reader and a blank low-frequency RFID door card, then read out the information of the community door card and re write the blank low-frequency door card

if you don't have a usable low-frequency door card in your hand, it's not difficult in theory to crack this system if you want to drive 100000 people to work. As long as you use a special low-frequency card that can constantly change your output signal and keep trying on the card reader. However, this is almost impossible in practice, because assuming that it takes 0.1s to read the card every time, if you want to obtain permission through experiments, you can only try 860000 numbers a day and a night, and I'm afraid you can't finish trying more than a dozen numbers until the day the earth stops rotating

(picture from the Internet)

this plaintext RFID access control system has been almost completely eliminated in Europe and the United States due to its low safety factor, but it is still widely used in China due to its low price. This should be a kind of sadness

why haven't you changed your door card

have you noticed that RFID access control is only used in office buildings or community gates, and few people use RFID to replace mechanical locks in their homes. In addition to the main reason that mechanical locks are cheaper than RFID electronic locks, there are the following reasons:

1 But the result has a certain error. The electronic lock needs power supply. Whether using batteries or mains power, it is always impossible to avoid the problem of power failure. No one should use the door lock that can't get into the house when there is a power failure

(picture from the network)

2 Compared with mechanical locks, electronic locks are usually more complex, so the reliability is usually worse, and the requirements for the working environment are also more stringent. As a result, the failure rate of electronic lock will be higher than that of mechanical lock

3. One of the main reasons why office buildings or companies use access control systems is that they are easy to manage, while residential buildings usually do not have this demand

the access control system using RFID door cards is safer than mechanical locks, and it is more difficult to crack. The access control system in office buildings is maintained by special personnel, and problems can be repaired in time, so office buildings usually choose the access control system. If it is a residential lock, the reliability of the door lock will be higher than the safety. After all, no one wants to be locked outside their own home

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