# Master lock auto-cracker built as coursework at University

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!

# How to crack a Master lock

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.