A common trope in bank heist B-movies is someone effortlessly bypassing a safe’s combination lock. Typically, the hero or villain will turn the dial while listening to the internal machinery, then deduce the combination based on sounds made by the lock. In real life, high-quality combination locks are not vulnerable to such simple attacks, but cheap ones can often be bypassed with a minimum of effort. Some are so simple that this process can even be automated, as [Mew463] has shown by building a machine that can open a Master combination lock in less than a minute.
The operating principle is based on research by Samy Kamkar from a couple of years ago. For certain types of Master locks, the combination can be found by applying a small amount of pressure on the shackle and searching for locations on the dial where its movement becomes heavier. A simple algorithm can then be used to completely determine the first and third numbers, and find a list of just eight candidates for the second number.
[Mew463]’s machine automates this process by turning the dial with a stepper motor and pulling on the shackle using a servo and a rack-and-pinion system. A magnetic encoder is mounted on the stepper motor to determine when the motor stalls, while the servo has its internal position encoder brought out as a means of detecting how far the shackle has moved. All of this is controlled by an Arduino Nano mounted on a custom PCB together with a TMC2208 stepper driver.
The machine does its job smoothly and quickly, as you can see in the (silent) video embedded below. All design files are available on the project’s GitHub page, so if you’ve got a drawer full of these locks without combinations, here’s your chance to make them sort-of-useful again. After all, these locks’ vulnerabilities have a long history, and we’ve even seen automated crackers before.
Continue reading “Robot Opens Master Combination Locks In Less Than A Minute”
We love the beginning of May because the final projects for college coursework start rolling into our tips line. Here’s one of the latest, it’s an automatic Master lock combination cracker which was built by [Ross Aiken] and his classmates as part of their ECE453 Embedded Microprocessor System Design class at the University of Wisconsin – Madison.
We’ve talked about the ease with which these locks can be cracked. But [Ross] points out that the resources we linked to before are flawed. To get the combination as quickly as possible the team has implemented an algorithm discussed here. Their machine uses a stepper motor to turn the dial with a big solenoid to pull on the shackle. The system is sensitive enough to detect the “sticky” spots of the lock, which are then used to narrow the number of possible combinations before brute forcing the combination. As you can see in the video after the break, the shackle moves slightly when pulled after an incorrect combination. The long vertical pin near the solenoid will pass through an optical sensor when the correct combination is found.
Do you have your own final project to show off? What are you waiting for, send us a tip about it!
Continue reading “Master Lock Auto-cracker Built As Coursework At University”
Long, long ago we covered a method to crack a Master lock in about 30 minutes or less. Here’s a revival of the same method but now the instructions to retrieve the combination are in info-graphic format created by [Mark Edward Campos].
If you didn’t get to try this the first time around, here’s how it works: A combination of a physical vulnerability, math, and brute force is used. First, the final number of the code can be obtained by pulling up on the latch while the dial is rotated. Because of the way the lock is built the correct number can be extrapolated using this trick. Secondly, a table of all possible first and second number combinations has been calculated for you. Third, it’s your job to brute force the correct table of possibilities which includes only about one hundred combinations.
We’re not really into felony theft and hopefully you’re not either. But, we have a nasty habit of needing to use a combination lock that’s been in a drawer for a few years and having no idea of what the correct code might be.
Update: We’ve had a lot of comments about shimming as a better method. For your enjoyment we’ve embedded a video after the break that details how to shim a Master lock using a beer can. Just remember: friends don’t let friends drink and shim.
Continue reading “How To Crack A Master Lock”